I've been playing around with Android Studio and I'm trying to implement a simple chronometer with the Chronometer widget. First I tried this code:
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.widget.Chronometer;
import android.view.View;
public class MainActivity extends AppCompatActivity {
Chronometer chrono;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
chrono = (Chronometer) findViewById(R.id.chronometer);
setContentView(R.layout.activity_main);
}
public void startChrono(View view) {
chrono.start();
}
public void stopChrono(View view) {
chrono.stop();
}
}
But when I used it, whenever I pressed the Start button, it would crash the app. Then I found this implementation online:
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.widget.Chronometer;
import android.view.View;
public class MainActivity extends AppCompatActivity {
Chronometer chrono;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
public void startChrono(View view) {
((Chronometer) findViewById(R.id.chronometer)).start();
}
public void stopChrono(View view) {
((Chronometer) findViewById(R.id.chronometer)).start();
}
}
This one works though, can anyone point out the differences between creating the Chronometer object in onCreate as opposed to what the second block of code does?
java.lang.IllegalStateException: Could not execute method of the activity
at android.view.View$1.onClick(View.java:4020)
at android.view.View.performClick(View.java:4780)
at android.view.View$PerformClick.run(View.java:19866)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5257)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)
Caused by: java.lang.reflect.InvocationTargetException
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at android.view.View$1.onClick(View.java:4015)
at android.view.View.performClick(View.java:4780)
at android.view.View$PerformClick.run(View.java:19866)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5257)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Chronometer.start()' on a null object reference
at com.example.mykongee.testchronometer.MainActivity.startChrono(MainActivity.java:22)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at android.view.View$1.onClick(View.java:4015)
at android.view.View.performClick(View.java:4780)
at android.view.View$PerformClick.run(View.java:19866)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5257)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)
Your issue is here:
chrono = (Chronometer) findViewById(R.id.chronometer);
setContentView(R.layout.activity_main);
You can not call findViewById before you call setContentLayout, because there is no view to find.
You app would have crashed with a NullPointerException because chrono was null.
In your first example, try swapping these two lines, and it will work the same as the second
setContentView(R.layout.activity_main);
chrono = (Chronometer) findViewById(R.id.chronometer);
In the future, do not simply say it didnt work, Android provides an amazong LogCat that tells you pretty much EXACTLY what the problem is.
If you can not decode the error yourself, then post the stacktrace provided by logcat.
In the first one you are first trying to get a reference to chrono, then you are setting your layout. The thing is, you can't get a reference without setting the layout first (can't find what isn't there...)
false:
chrono = (Chronometer) findViewById(R.id.chronometer);
setContentView(R.layout.activity_main);
correct:
setContentView(R.layout.activity_main);
chrono = (Chronometer) findViewById(R.id.chronometer);
In the second example you are setting the layout, then on button press you find the reference, so everything is ok.
Related
I've some problems trying to do G+ Signin. I think the G+ button isn't working.
I've tried to clean the project too.
IDE: Android Studio 1.1.0
Play Services: 6.5.87
Thx.
--
LoginActivity:
package com.nimbus.podchest;
import android.os.Bundle;
import android.support.v4.app.FragmentActivity;
import android.view.View;
import com.google.android.gms.common.ConnectionResult;
import com.google.android.gms.common.SignInButton;
import com.google.android.gms.common.api.GoogleApiClient;
import com.google.android.gms.plus.Plus;
public class LoginActivity extends FragmentActivity implements GoogleApiClient.ConnectionCallbacks,
GoogleApiClient.OnConnectionFailedListener {
private GoogleApiClient mGoogleApiClient;
private SignInButton SignInButton;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_login);
// Create a GoogleApiClient instance
mGoogleApiClient = new GoogleApiClient.Builder(this)
.addApi(Plus.API)
.addScope(Plus.SCOPE_PLUS_LOGIN)
.addConnectionCallbacks(this)
.addOnConnectionFailedListener(this)
.build();
SignInButton = (SignInButton) findViewById(R.id.sign_in_button);
SignInButton.setOnClickListener((android.view.View.OnClickListener) this);
}
public void onClick(View view) {
if (view.getId() == R.id.sign_in_button) {
mGoogleApiClient.connect();
}
}
#Override
protected void onStart() {
super.onStart();
mGoogleApiClient.connect();
}
#Override
protected void onStop() {
mGoogleApiClient.disconnect();
super.onStop();
}
#Override
public void onConnected(Bundle connectionHint) {
// Connected to Google Play services!
// The good stuff goes here.
}
#Override
public void onConnectionSuspended(int cause) {
// The connection has been interrupted.
// Disable any UI components that depend on Google APIs
// until onConnected() is called.
}
#Override
public void onConnectionFailed(ConnectionResult result) {
// This callback is important for handling errors that
// may occur while attempting to connect with Google.
//
// More about this in the next section.
}
}
Logcat:
03-10 23:58:26.747 10123-10123/com.nimbus.podchest E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: com.nimbus.podchest, PID: 10123
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.nimbus.podchest/com.nimbus.podchest.LoginActivity}: java.lang.ClassCastException: com.nimbus.podchest.LoginActivity cannot be cast to android.view.View$OnClickListener
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2314)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2388)
at android.app.ActivityThread.access$800(ActivityThread.java:148)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1292)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5312)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:901)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:696)
Caused by: java.lang.ClassCastException: com.nimbus.podchest.LoginActivity cannot be cast to android.view.View$OnClickListener
at com.nimbus.podchest.LoginActivity.onCreate(LoginActivity.java:25)
at android.app.Activity.performCreate(Activity.java:5953)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1128)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2267)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2388)
at android.app.ActivityThread.access$800(ActivityThread.java:148)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1292)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5312)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:901)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:696)
03-11 00:00:13.565 11822-11822/com.nimbus.podchest E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: com.nimbus.podchest, PID: 11822
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.nimbus.podchest/com.nimbus.podchest.LoginActivity}: java.lang.ClassCastException: com.nimbus.podchest.LoginActivity cannot be cast to android.view.View$OnClickListener
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2314)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2388)
at android.app.ActivityThread.access$800(ActivityThread.java:148)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1292)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5312)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:901)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:696)
Caused by: java.lang.ClassCastException: com.nimbus.podchest.LoginActivity cannot be cast to android.view.View$OnClickListener
at com.nimbus.podchest.LoginActivity.onCreate(LoginActivity.java:35)
at android.app.Activity.performCreate(Activity.java:5953)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1128)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2267)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2388)
at android.app.ActivityThread.access$800(ActivityThread.java:148)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1292)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5312)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:901)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:696)
If you read the Logcat you can see that you have a problem here :
com.nimbus.podchest.LoginActivity.onCreate(LoginActivity.java:25)
So at line 25 in onCreate function you are trying to cast your activity (LoginActivity) to android.view.View$OnClickListener. You can't cast this class like this since there are not related.
You need to add implements OnClickListener on the definition of your LoginActivity class to make your cast work.
And now you will be able to just pass your current Activity to register to the listener:
SignInButton.setOnClickListener(this);
I was trying to make a ListView of reminder notes. But when I try to save it and display it in a ListView, app crashes with this error/exception. saveNote method is called when you press save button. Any help is appreciated.
public boolean onOptionsItemSelected(MenuItem item) {
int id = item.getItemId();
switch(id) {
case R.id.add_reminder : {
et = (EditText)findViewById(R.id.new_note);
et.setVisibility(View.VISIBLE);
note = et.getText().toString();
i++;
Button save_button = (Button) findViewById(R.id.button_save);
save_button.setVisibility(View.VISIBLE);
}
default : return super.onOptionsItemSelected(item);
}
}
public void saveNote(View view) {
String[] notes = new String[20];
notes[i] = note;
listView = (ListView) findViewById(R.id.list);
ArrayAdapter<String> adapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, android.R.id.text1,notes);
listView.setAdapter(adapter);
listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
#Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
//Clicked item index
int itemPosition = position;
//Clicked item value
String itemNote = (String) listView.getItemAtPosition(position);
//Alert
Toast.makeText(getApplicationContext(), "Position :" + itemPosition + " ListItem : " + itemNote, Toast.LENGTH_LONG).show();
}
});
Logcat
java.lang.IllegalStateException: Could not execute method of the activity
at android.view.View$1.onClick(View.java:4020)
at android.view.View.performClick(View.java:4780)
at android.view.View$PerformClick.run(View.java:19866)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5257)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)
Caused by: java.lang.reflect.InvocationTargetException
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at android.view.View$1.onClick(View.java:4015)
at android.view.View.performClick(View.java:4780)
at android.view.View$PerformClick.run(View.java:19866)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5257)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ListView.setAdapter(android.widget.ListAdapter)' on a null object reference
at com.cokosofts.pramith.reminder.MainActivity.saveNote(MainActivity.java:69)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at android.view.View$1.onClick(View.java:4015)
at android.view.View.performClick(View.java:4780)
at android.view.View$PerformClick.run(View.java:19866)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5257)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)
The main cause which I found from the Logs is ListView is null. Please check one more time if the listView is empty or not? Also what is notes[i] = note ??
I think in each Save button click you are finding ListView and the setting Adapter each time. This is not a good approach from my point of view. You should set the adapter very first time and next time just update your adapter data and call notifyDataSetChanged();
Debug and find out why your ListView was not found on your layout (was null).
Problem is with following line:
listView = (ListView) findViewById(R.id.list);
Please check whether your xml has ListView widget with id as 'list' .
If id is different in XML it will result in a NULL object reference. When you call
listView.setAdapter(adapter)
It will give a NULL pointer exception.
I am getting Null Pointer Exception on line 219: amanager.setStreamMute(AudioManager.STREAM_NOTIFICATION, true);. It was not happening before, today i saw it first time, i am using Android 5.0. Code mutes notification sound when activity starts and unmutes when it is destroyed.
Code:
private AudioManager amanager;
#Override
protected void onCreate(Bundle savedInstanceState) {
amanager=(AudioManager)getSystemService(Context.AUDIO_SERVICE);
}
#Override
protected void onResume() {
super.onResume();
if(amanager!=null) {
amanager.setStreamMute(AudioManager.STREAM_NOTIFICATION, true);
}
}
#Override
protected void onPause() {
if(amanager!=null) {
amanager.setStreamMute(AudioManager.STREAM_NOTIFICATION, false);
}
super.onPause();
}
Error:
java.lang.RuntimeException: Unable to resume activity {com.jemshit.itu/com.jemshit.nfcAttendance.ClassActivity}: java.lang.NullPointerException: Null pointer exception during instruction 'invoke-static {v0}, android.os.IBinder android.media.AudioService$VolumeStreamState$VolumeDeathHandler.access$5300(android.media.AudioService$VolumeStreamState$VolumeDeathHandler) // method#11492'
at android.app.ActivityThread.performResumeActivity(ActivityThread.java:3346)
at android.app.ActivityThread.handleResumeActivity(ActivityThread.java:3377)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2728)
at android.app.ActivityThread.access$900(ActivityThread.java:172)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1422)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:145)
at android.app.ActivityThread.main(ActivityThread.java:5832)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1399)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1194)
Caused by: java.lang.NullPointerException: Null pointer exception during instruction 'invoke-static {v0}, android.os.IBinder android.media.AudioService$VolumeStreamState$VolumeDeathHandler.access$5300(android.media.AudioService$VolumeStreamState$VolumeDeathHandler) // method#11492'
at android.os.Parcel.readException(Parcel.java:1546)
at android.os.Parcel.readException(Parcel.java:1493)
at android.media.IAudioService$Stub$Proxy.setStreamMute(IAudioService.java:992)
at android.media.AudioManager.setStreamMute(AudioManager.java:1466)
at com.jemshit.nfcAttendance.ClassActivity.onResume(ClassActivity.java:219)
at android.app.Instrumentation.callActivityOnResume(Instrumentation.java:1255)
at android.app.Activity.performResume(Activity.java:6338)
at android.app.ActivityThread.performResumeActivity(ActivityThread.java:3335)
at android.app.ActivityThread.handleResumeActivity(ActivityThread.java:3377)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2728)
at android.app.ActivityThread.access$900(ActivityThread.java:172)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1422)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:145)
at android.app.ActivityThread.main(ActivityThread.java:5832)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1399)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1194)
It's an Android bug it's not your code. Put a try/catch block in your code to avoid the crash.
I am trying to make a simple timer using the Timer and TimerTask classes. I keep getting the following error:
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.view.Window.findViewById(int)' on a null object reference
Here is my code:
package com.austinheitmann.stopwatch;
import android.os.CountDownTimer;
import android.os.SystemClock;
import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.TextView;
import java.util.Timer;
import java.util.TimerTask;
public class MainActivity extends ActionBarActivity {
TextView timerf;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
timerf = (TextView) findViewById(R.id.timer);
}
int i=0;
TimerTask time = new TimerTask() {
public void run() {
i++;
int k = i/60;
int j = i%60;
if (j>9) {
timerf.setText("seconds remaining: " + k + ":" + j);
}else {
timerf.setText("seconds remaining: " + k + ":0" + j);
}
Log.d("Uhh", "Sec:" + i);
}
};
Timer timers = new Timer();
public void startB(View view) {
timers.schedule(time, 100000000, 1000);
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_main, menu);
return true;
}
#Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
//noinspection SimplifiableIfStatement
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
}
}
Here is the xml file(layout):
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent"
android:layout_height="match_parent" android:paddingLeft="#dimen/activity_horizontal_margin"
android:paddingRight="#dimen/activity_horizontal_margin"
android:paddingTop="#dimen/activity_vertical_margin"
android:paddingBottom="#dimen/activity_vertical_margin" tools:context=".MainActivity">
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:textAppearance="?android:attr/textAppearanceLarge"
android:text="0:00"
android:id="#+id/timer"
android:layout_alignParentTop="true"
android:layout_centerHorizontal="true"
android:layout_marginTop="54dp" />
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Start/Pause"
android:id="#+id/start"
android:layout_below="#+id/timer"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true"
android:layout_marginTop="119dp"
android:onClick="startB"/>
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Stop/Reset"
android:id="#+id/stop"
android:layout_alignBottom="#+id/start"
android:layout_alignParentRight="true"
android:layout_alignParentEnd="true" />
</RelativeLayout>
Every solution I have seen to this error has to do with the layout but I am not altering that in anyway. I have moved to the TimerTask in the startB class also and get the same error. How can I fix this error?
Here's the entire error I get from one run after clearing the logcat (I put ** where the error occurs at):
01-16 12:27:21.008 2455-2455/com.austinheitmann.stopwatch I/art﹕ Not late-enabling -Xcheck:jni (already on)
01-16 12:27:21.119 2455-2455/com.austinheitmann.stopwatch D/AndroidRuntime﹕ Shutting down VM
--------- beginning of crash
01-16 12:27:21.123 2455-2455/com.austinheitmann.stopwatch E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: com.austinheitmann.stopwatch, PID: 2455
java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.austinheitmann.stopwatch/com.austinheitmann.stopwatch.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.view.Window.findViewById(int)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2209)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
at android.app.ActivityThread.access$800(ActivityThread.java:144)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5221)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.view.Window.findViewById(int)' on a null object reference
at android.app.Activity.findViewById(Activity.java:2071)
at com.austinheitmann.stopwatch.MainActivity.<init>(MainActivity.java:25)
at java.lang.reflect.Constructor.newInstance(Native Method)
at java.lang.Class.newInstance(Class.java:1572)
at android.app.Instrumentation.newActivity(Instrumentation.java:1065)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2199)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
at android.app.ActivityThread.access$800(ActivityThread.java:144)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5221)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
01-16 12:44:57.778 2582-2582/com.austinheitmann.stopwatch D/AndroidRuntime﹕ Shutting down VM
01-16 12:44:57.778 2582-2582/com.austinheitmann.stopwatch E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: com.austinheitmann.stopwatch, PID: 2582
java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.austinheitmann.stopwatch/com.austinheitmann.stopwatch.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.view.Window.findViewById(int)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2209)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
at android.app.ActivityThread.access$800(ActivityThread.java:144)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5221)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.view.Window.findViewById(int)' on a null object reference
at android.app.Activity.findViewById(Activity.java:2071)
at com.austinheitmann.stopwatch.MainActivity.<init>(MainActivity.java:25)
at java.lang.reflect.Constructor.newInstance(Native Method)
at java.lang.Class.newInstance(Class.java:1572)
at android.app.Instrumentation.newActivity(Instrumentation.java:1065)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2199)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
at android.app.ActivityThread.access$800(ActivityThread.java:144)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5221)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
01-16 12:46:25.059 2641-2641/com.austinheitmann.stopwatch D/AndroidRuntime﹕ Shutting down VM
01-16 12:46:25.059 2641-2641/com.austinheitmann.stopwatch E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: com.austinheitmann.stopwatch, PID: 2641
java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.austinheitmann.stopwatch/com.austinheitmann.stopwatch.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.view.Window.findViewById(int)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2209)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
at android.app.ActivityThread.access$800(ActivityThread.java:144)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5221)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.view.Window.findViewById(int)' on a null object reference
at android.app.Activity.findViewById(Activity.java:2071)
at com.austinheitmann.stopwatch.MainActivity.<init>(MainActivity.java:25)
at java.lang.reflect.Constructor.newInstance(Native Method)
at java.lang.Class.newInstance(Class.java:1572)
at android.app.Instrumentation.newActivity(Instrumentation.java:1065)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2199)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
at android.app.ActivityThread.access$800(ActivityThread.java:144)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5221)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
01-16 12:47:50.630 2702-2702/com.austinheitmann.stopwatch D/AndroidRuntime﹕ Shutting down VM
01-16 12:47:50.630 2702-2702/com.austinheitmann.stopwatch E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: com.austinheitmann.stopwatch, PID: 2702
java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.austinheitmann.stopwatch/com.austinheitmann.stopwatch.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.view.Window.findViewById(int)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2209)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
at android.app.ActivityThread.access$800(ActivityThread.java:144)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5221)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
**Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.view.Window.findViewById(int)' on a null object reference**
at android.app.Activity.findViewById(Activity.java:2071)
at com.austinheitmann.stopwatch.MainActivity.<init>(MainActivity.java:25)
at java.lang.reflect.Constructor.newInstance(Native Method)
at java.lang.Class.newInstance(Class.java:1572)
at android.app.Instrumentation.newActivity(Instrumentation.java:1065)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2199)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
at android.app.ActivityThread.access$800(ActivityThread.java:144)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5221)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
You are trying to findViewById before the activity's context is ready.
If you want to access timerf in other methods too, create a class member but make the initialization in the onCreate after setContentView:
TextView timerf;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
timerf = (TextView) findViewById(R.id.timer);
}
Update:
I didn't notice the other class member variables you're instantiating. They are referencing timerf which null.
You need to initialize them in the onCreate too. Here's the full code that should work:
package com.austinheitmann.stopwatch;
import android.os.CountDownTimer;
import android.os.SystemClock;
import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.TextView;
import java.util.Timer;
import java.util.TimerTask;
public class MainActivity extends ActionBarActivity {
Timer timers = new Timer();
TextView timerf;
TimerTask time;
int i=0;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
timerf = (TextView) findViewById(R.id.timer);
time = new TimerTask() {
public void run() {
i++;
int k = i/60;
int j = i%60;
if (j>9) {
timerf.setText("seconds remaining: " + k + ":" + j);
}else {
timerf.setText("seconds remaining: " + k + ":0" + j);
}
Log.d("Uhh", "Sec:" + i);
}
};
}
public void startB(View view) {
timers.schedule(time, 100000000, 1000);
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_main, menu);
return true;
}
#Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
//noinspection SimplifiableIfStatement
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
}
First of you use the constructor public MainActivity()and
Timer timer; and long startTime; long stopTime Declare Gobble variable
public MainActivity() {
timer = new Timer();
startTime = System.currentTimeMillis();
stopTime = 0;
}
I'm currently trying to implement Material Design activity transitions. For a reason i really don't know, it crashes. Can someone give me a clue? (I don't know if it's important, but inside my MainActivity, i've a ViewPager with Fragments from which I try to start the next Activity)
Thanks a lot for your help.
My code:
public class MainActivity extends ActionBarActivity implements ActionBar.TabListener {
(...)
#Override
protected void onCreate(Bundle savedInstanceState) {
Log.i("TAAG", "MainActivity::onCreate1");
super.onCreate(savedInstanceState);
Log.i("TAAG", "MainActivity::onCreate2");
getWindow().requestFeature(Window.FEATURE_CONTENT_TRANSITIONS);
Log.i("TAAG", "MainActivity::onCreate3");
setContentView(R.layout.activity_main);
Log.i("TAAG", "MainActivity::onCreate4");
(...)
}
Here are the logs:
11-13 18:12:36.442 1098-1098/I/TAAG﹕ MainActivity::onCreate1
11-13 18:12:36.544 1098-1098/I/TAAG﹕ MainActivity::onCreate2
11-13 18:12:36.559 1098-1098/E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: mypackage, PID: 1098
java.lang.RuntimeException: Unable to start activity ComponentInfo{mypackage/mypackage.MainActivity}: android.util.AndroidRuntimeException: requestFeature() must be called before adding content
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2298)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
at android.app.ActivityThread.access$800(ActivityThread.java:144)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5221)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
Caused by: android.util.AndroidRuntimeException: requestFeature() must be called before adding content
at com.android.internal.policy.impl.PhoneWindow.requestFeature(PhoneWindow.java:301)
at mypackage.MainActivity.onCreate(MainActivity.java:42)
at android.app.Activity.performCreate(Activity.java:5933)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1105)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2251)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
at android.app.ActivityThread.access$800(ActivityThread.java:144)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5221)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
Try calling getWindow().requestFeature(Window.FEATURE_CONTENT_TRANSITIONS); before super.onCreate().