package com.iperetz1.android.testbutton1;
import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
public class TestButton extends Activity {
/** Called when the activity is first created. */
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
Button test2 = (Button)findViewById(R.id.test2);
test2.setOnClickListener(new OnClickListener()
{
#Override
public void onClick(View v)
{
setContentView(R.layout.test2);;
}
});
Button other = (Button)findViewById(R.id.backmain);
other.setOnClickListener(new OnClickListener()
{
#Override
public void onClick(View v)
{
setContentView(R.layout.main);;
}
});
}
}
main.xls
<?xml version="1.0" encoding="utf-8"?>
<AbsoluteLayout
android:id="#+id/widget0"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
xmlns:android="http://schemas.android.com/apk/res/android"
>
<Button
android:id="#+id/test2"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="test2"
android:layout_x="24px"
android:layout_y="165px"
>
</Button>
</AbsoluteLayout>
test2.xml
<?xml version="1.0" encoding="utf-8"?>
<AbsoluteLayout
android:id="#+id/widget0"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
xmlns:android="http://schemas.android.com/apk/res/android"
>
<Button
android:id="#+id/backmain"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="backmain"
android:layout_x="24px"
android:layout_y="165px"
>
</Button>
</AbsoluteLayout>
findViewById is a lot simpler than people tend to think it is. It traverses the view hierarchy looking for a view with the given ID. If it's not found, findViewById returns null.
You started by setting the content view to your main layout but later on you tried to findViewById(R.id.backmain). Since there is no view with that ID in your main layout, it returns null. At that point attempting other.setOnClickListener will fail. You will only be able to do this when your button actually exists in the view hierarchy.
There's nothing inherently wrong with dynamically changing your view hierarchy, but you'll have to handle some things differently if you go that route. (Such as when you wire up events to views that don't exist during onCreate like you're trying to do above.)
As #Cristian Castiblanco said, changing the view dynamically is causing the problem, for these kind of scenarios, you have to create separate activities and invoke them using intents and pass data between them using bundles.
Related
I surdenly noticed that My project starts throwing error anytime I try to access a resources that is a button. It underlines R.id.button. I dont understand why. I even deleted the last xml that I created but problem persist.
This is an example of my xml file
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="#drawable/layoutborder"
android:orientation="vertical" >
<TextView
android:id="#+id/chat"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_margin="10dp"
android:text="#string/stepone"
android:textAppearance="?android:attr/textAppearanceMedium"
android:textColor="#color/wine" />
<ImageView
android:id="#+id/imageView1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_margin="10dp"
android:src="#drawable/ai" />
<Button
android:id="#+id/drugdetails"
style="#style/smallButtonStyleBlackpearl"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginLeft="20dp"
android:layout_marginRight="20dp"
android:layout_marginTop="10dp"
android:text="#string/nextbut" />
</LinearLayout>
My Java code
package com.example.rhemahealthcare;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import com.actionbarsherlock.app.SherlockActivity;
import com.example.rhemahealthcare.R;
public class SteponeActivity extends SherlockActivity{
#Override
public void onCreate(Bundle savedInstanceState){
super.onCreate(savedInstanceState);
setContentView(R.layout.steponeactivity);
final Button button = (Button)findViewById(R.id.button1);
button.setOnClickListener(new OnClickListener(){
#Override
public void onClick(View v){
// TODO Auto-generated method stub
Intent intent = new Intent(SteponeActivity.this,SteptwoActivity.class);
startActivity(intent);
}
});
}
}
i think you change any button1 id buy clicking right click and choose edit id. this option changes all the ids with that name in all the layouts.
As #Aleks G gussed it right in the comment, you don't have any button with id as button1 in your xml file. You've mentioned it :
final Button button = (Button)findViewById(R.id.button1);
Use the appropriate ID or put one in your layout file.
I have figured out the problem. My button ids were automatically change to button1 so they did not reference their previous ids that I gave to them. Thanks alot
eveything looks to be fine, but I still get error when I try to change the view by pressing the button.
Here is code:
package com.example.testy;
import android.os.Bundle;
import android.app.Activity;
import android.view.Menu;
import android.view.View;
import android.widget.ViewFlipper;
public class MainActivity extends Activity {
ViewFlipper flipper;
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
flipper = (ViewFlipper) findViewById(R.id.viewFlipper1);
setContentView(R.layout.activity_main);
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.activity_main, menu);
return true;
}
public void clcik(View v) {
flipper.showNext();
}
}
And here is my XML:
<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:gravity="top" >
<ViewFlipper
android:id="#+id/viewFlipper1"
android:layout_width="match_parent"
android:layout_height="match_parent" >
<Button
android:id="#+id/button1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:onClick="click"
android:text="Button!!" />
<TextView
android:id="#+id/textView1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="TextView!!" />
</ViewFlipper>
</RelativeLayout>
Anyone knows what can be wrong in this code?
Thank you for answers!
Perhaps you should fix the name of your method to click ?
public void **clcik**(View v) {
flipper.showNext();
}
Due the wrong spell (clcik) in our activity code, you may be getting a Exception because Android can't find the click method.
And thanks to #yugidroid's answer I spot one more error on your code:
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
flipper = (ViewFlipper) findViewById(R.id.viewFlipper1);
setContentView(R.layout.activity_main);
}
You call findViewById before even you have any Views (a call to setContentView) . You will get a NullPointException because of that.
I would recommend you to make a call to super.onCreate the very first line of your onCreate() method. That is what Google does.
Regarding setting the click listener on layout or creating a listener and setting on the code. Well, there is not much difference, although the latter is certainly faster as the first uses reflection, what has a higher cost than just calling a method.
First of all, make sure you call setContentView(R.layout.activity_main); after the super, its a good practice.
Your problem is that you set android:onClick="click" but you are refering the wrong method in Java (clcik doesn't exists).
I advice you to declare and set listeners in the activity, not in the xml.
This is a Major Edit on my previous question
I'm creating a custom (composite) component named OneLineSeeker that consists of a TextView and a SeekBar.
When I have multiple OneLineSeekers declared in a layout, they don't retain their state on configuration change. All seeker thumbs assume the same position (the position of the last OneLineSeeker) on configuration change.
If I don't use the custom component and use only SeekBars individually (uncomment //a() in main activity), they will retain their individual positions on configuration change.
Can anyone help?
src files
A_seekbarsActivity.java
package com.an;
import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.SeekBar;
public class A_seekbarsActivity extends Activity {
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
//a();
}
void a() {
setContentView(R.layout.main_1);
Button b = (Button) findViewById(R.id.button1);
b.setOnClickListener(new OnClickListener() {
#Override
public void onClick(View v) {
SeekBar sb = (SeekBar) findViewById(R.id.seekBar1);
if(sb.getProgress() > 50) sb.setProgress(0);
else sb.incrementProgressBy(5);
}
});
}
}
OneLineSeeker.java
package com.an;
import android.content.Context;
import android.content.res.TypedArray;
import android.util.AttributeSet;
import android.view.LayoutInflater;
import android.view.View;
import android.widget.LinearLayout;
import android.widget.TextView;
public class OneLineSeeker extends LinearLayout {
public OneLineSeeker(Context context, AttributeSet attrs) {
super(context, attrs);
View ols = LayoutInflater.from(context).inflate(R.layout.one_line_seeker, this, true);
TypedArray array = context.obtainStyledAttributes(attrs, R.styleable.OneLineSeeker, 0, 0);
String text = array.getString(R.styleable.OneLineSeeker_name);
if (text != null)
((TextView) ols.findViewById(R.id.name)).setText(text);
array.recycle();
}
}
res/layout files
main_1.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
>
<SeekBar android:id="#+id/seekBar1" android:layout_height="wrap_content" android:layout_width="match_parent"></SeekBar>
<SeekBar android:id="#+id/seekBar2" android:layout_height="wrap_content" android:layout_width="match_parent"></SeekBar>
<SeekBar android:id="#+id/seekBar3" android:layout_height="wrap_content" android:layout_width="match_parent"></SeekBar>
<Button android:text="Button" android:id="#+id/button1" android:layout_width="wrap_content" android:layout_height="wrap_content"></Button>
</LinearLayout>
main.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:oneLineSeeker="http://schemas.android.com/apk/res/com.an"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
>
<com.an.OneLineSeeker
android:id="#+id/s1"
android:layout_width="match_parent"
android:layout_height="wrap_content"
oneLineSeeker:name="1"
/>
<com.an.OneLineSeeker
android:id="#+id/s2"
android:layout_width="match_parent"
android:layout_height="wrap_content"
oneLineSeeker:name="2"
/>
<com.an.OneLineSeeker
android:id="#+id/s3"
android:layout_width="match_parent"
android:layout_height="wrap_content"
oneLineSeeker:name='3'
/>
</LinearLayout>
one_line_seeker.xml
<?xml version="1.0" encoding="utf-8"?>
<merge
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="wrap_content"
>
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id='#+id/name'
android:text='name'
/>
<SeekBar
android:id='#+id/seekbar'
android:layout_width="match_parent"
android:layout_height="match_parent"
/>
</merge>
res/values files
attrs.xml
<?xml version="1.0" encoding="utf-8"?>
<resources>
<declare-styleable name="OneLineSeeker">
<attr name="name" format="string"/>
</declare-styleable>
</resources>
Its not supposed to reset its position to zero. This is actually a feature. When view has id associated with, it usually saves and the restores its state on configuration changes.
If you don't want specific view to save state on configuration change, you can remove android:id from view's entry in layout (but you won't be able to control that view then). Another alternative is to extend ProgressBar and disable its ability to restore state.
The last one option is the easiest one: override onRestoreInstanceState() and reset state there:
#Override
protected void onRestoreInstanceState(Bundle savedInstanceState)
{
super.onRestoreInstanceState(savedInstanceState);
bar.setProgress(0);
}
But I would strongly recommend not resetting view state. After all the whole idea of restoring state on configuration change is to make user think as if nothing really changed. And you need to have very strong reasons to disable this behavior.
In that u have to define Orientation Change Methods.....
public void onConfigurationChanged(Configuration newConfig) {
super.onConfigurationChanged(newConfig);
onCreate(null);
}
Try this Code may u get any Help.....
Ok this may seem like a pointless example but if I can figure this out then the program I am trying to make will work. So I have two activities test and test two each with one button.
Test 1:
package thompson.cameron.com;
import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
public class Test extends Activity implements OnClickListener {
/** Called when the activity is first created. */
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
View button = findViewById(R.id.testButton);
button.setOnClickListener(this);
}
public void onClick(View v){
Intent i = new Intent(this, Test2.class);
startActivity(i);
}
}
and test2
package thompson.cameron.com;
import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
public class Test2 extends Activity implements OnClickListener {
#Override
public void onCreate(Bundle savedInstanceState){
super.onCreate(savedInstanceState);
setContentView(R.layout.main2);
View test = findViewById(R.id.testButton);
test.setOnClickListener(this);
}
public void onClick(View v){
switch (v.getId()){
case R.id.testButton:
System.exit(1);
}
}
}
When I click the button on Test it is supposed to launch test2 however it is at this point I get an null pointer exception that I have narrowed down to test.setOnClickListener(this); line of code. Below are my two xml files for the layout. I can get the button to work when I only have one activity but as soon as I add a second activity with a different layout file it all falls apart
main.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
>
<Button
android:id="#+id/testButton"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="TEST TEST TEST"/>
</LinearLayout>
main2.xml:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
>
<Button
android:id="#+id/testButton"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="TEST2 TEST2 TEST2"/>
</LinearLayout>
I'm still new at Android programming so thanks for all your help.
Open the Debug perspective in Eclipse
Choose the 'Breakpoints' view tab.
Select the 'Add Java Exception Breakpoint' and choose
NullPointerException.
Launch your activity, either by using 'Debug As...' or attaching
the debugger to a running instance via DDMS.
Execute the offending workflow. It will break on the line that
caused the NullPointerException.
In your test.java file give:
implements View.OnClickListener
Initialize your button as:
Button testButton = (Button) findViewById(R.id.testButton);
and inside your onClick method, check whether you are clicking button:
if(v == testButton) {
//give ur intent code
}
There are different ways to perform onClick functionality.
One is the above method which I have mentioned.
Another one is what ankit has mentioned.
Third way is through your layout.
Inside your layout for your button tag, you may give as:
<Button android:id="#+id/testButton" android:layout_height="wrap_content" android:layout_width="wrap_content" android:text="Click" android:onClick="onTestButtonClick" />
And inside your class just mention the below details for button:
public void onTestButtonClick(View view) {
//give your intent code
}
You may refer to the link also:
http://android-developers.blogspot.com/2009/10/ui-framework-changes-in-android-16.html
Make sure that both activities are register at the application's manifest file.
As a side note never call System.exit in your code. You can call finish() to close an Activity and this will bring at the front the previous Activity on the stack.
The issue here is that you haven't typecasted your views to buttons.
import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button; // Needed to add this import for the button casting below
public class Test extends Activity implements OnClickListener {
/** Called when the activity is first created. */
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
// I have changed View to Button and then typecasted
// with the "(Button)" the return of findViewById
Button button = (Button) findViewById(R.id.testButton);
button.setOnClickListener(this);
}
public void onClick(View v){
Intent i = new Intent(this, Test2.class);
startActivity(i);
}
}
Let me know if you have any issues with this. I just completed my first experiment through using the onClickListener implementation through the main class instead of individual anonymous listeners.
Andrew
I had the same problem, you may put the same content view that the button,
setContentView(R.layout.main); if the button is in that content view, in other case, you will put:
setContentView(R.layout.buttoncontentview);
View button = findViewById(R.id.testButton);
button.setOnClickListener(this);
public void onClick(View v){
Intent i = new Intent(this, Test2.class);
startActivity(i);
}
setContentView(R.layout.main);
sorry for my bad english, but i'm spanish
Implement OnClickListener interface
and set button.setOnClickListener(this);
and override
public void onClick(View v) {
}
I think your buttons IDs need to be different in different activities. R.id.testButton would refer to only one button.
The final solution is that you may modify the AndroidManifest.xml file, i finally solved my error in this link How to register a new activity in AndroidManifest.xml?
You can try this.it may work.
package thompson.cameron.com;
import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
public class Test extends Activity{
private Button button;
/** Called when the activity is first created. */
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
button = findViewById(R.id.testButton);
button.setOnClickListener(new OnClickListener() {
public void onClick(View arg0) {
Intent i=new Intent().setClass(Test.this,Test2.class);
startActivity(i);
}
});
}
}
First of all in main.xml and main2.xml chage the button's ids like in below code.
main.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
>
<Button
android:id="#+id/testButton"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="TEST TEST TEST"/>
</LinearLayout>
main2.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
>
<Button
android:id="#+id/testButton1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="TEST2 TEST2 TEST2"/>
</LinearLayout>
It throws nullpointerexception because of id confict with each other so in your java file use following code to find button.
In Activity 1
Button button = findViewById(R.id.testButton);
button.setOnClickListener(this);
and
In Activity 2
Button button = findViewById(R.id.testButton1);
button.setOnClickListener(this);
I'm trying to get a simple onClick to fire from an ImageButton - it seems like a simple enough task, but I'm obviously missing something here.
Here is my java file:
package com.jlbeard.android.testapp;
import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.ImageButton;
import android.widget.Toast;
public class testapp extends Activity {
/** Called when the activity is first created. */
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
//handle the button press
ImageButton mainButton = (ImageButton) findViewById(R.id.mainButton);
mainButton.setOnClickListener(new OnClickListener() {
#Override
public void onClick(View v) {
//show message
Toast.makeText(testapp.this, "Button Pressed", Toast.LENGTH_LONG);
}
});
}
}
Here is my layout file:
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
>
<ImageView
android:id="#+id/whereToEat"
android:src="#drawable/where_to_eat"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_centerHorizontal="true"
android:layout_marginTop="8px"
/>
<ImageButton
android:id="#+id/mainButton"
android:src="#drawable/main_button"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_centerHorizontal="true"
android:layout_centerVertical="true"
android:background="#null"
android:clickable="true"
android:onClick="mainButtonClick"
/>
</RelativeLayout>
It seems to me that I'm missing something simple... but can't seem to figure it out. Thanks!
You didn't run show() method on Toast object. Very common mistake :-)
You also might have a problem due to the manifest setting onClick
android:onClick="mainButtonClick"
If mainButtonClick exists on post 1.5 devices it may be called instead, overriding the one you're setting in code
In my case, the imageButton was displayed behind a list. Because the list was empty, the ImageButton was seen but onClick was never fired.
Adding android:elevation="5dp" in the screen xml solve my problem
Note that if I use Button instead of ImageButton, elevation is not required.