Develop Reference

Android - changing textview from other activity

I'm quite new to programming.
I'm trying to make a simple app with two activities, where the second activity can change the text of the first. I know it can be done using intents, but I was wondering if there is a more direct way of doing it, for example using the second activity to call a function from the first activity?
Here's the code I have so far:
The MainActivity, which contains a TextView and a button to open the second activity:
public class MainActivity extends Activity {
TextView textview;
Button button;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
textview = (TextView) findViewById(R.id.et2);
button = (Button) findViewById(R.id.b1);
button.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
// TODO Auto-generated method stub
Intent intent = new Intent(MainActivity.this, ChangeText.class);
startActivity(intent);
}
});
}
#Override
protected void onPause() {
// TODO Auto-generated method stub
super.onPause();
}
#Override
protected void onResume() {
// TODO Auto-generated method stub
super.onResume();
}
public void changetext(String message) {
textview.setText(message);
}
}
And the second activity, ChangeText, which contains an EditText and a button which should change the text of the TextView in MainActivity and then finish itself:
public class ChangeText extends Activity{
EditText edittext;
Button button;
private MainActivity mainclass;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.change_text);
edittext = (EditText)findViewById(R.id.et2);
button = (Button)findViewById(R.id.b2);
button.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
// TODO Auto-generated method stub
String message = edittext.getText().toString();
mainclass.changetext(message);
finish();
}
});
}
}
As you can see I tried to make the app work by making a public function in MainActivity which receives a string and sets the TextView with it, and then I call this function from the ChangeText activity.
The problem: it keeps crashing! Can anyone tell me how I can make this work?

Seems like I answered almost exactly the same question a week or so ago, so this is probably a duplicate, but I can't seem to find the original question.
The short answer is no - you can't call a method in an Activity from another Activity. The issue is that for normal programming purposes, only one Activity exists at a time*.
If you do something to circumvent this, then you're risking causing some major issues, including high memory usage, null pointer exceptions, etc.
The correct way to do this is indeed through the Intent system.
* Activities may or may not actually get destroyed when they become inactive, depending on things like how you use the back stack.
However, you should always program is if they do get destroyed when they become inactive - read, understand, and respect the Activity lifecycle.

For something as simple as your app, the "most direct" approach is to use the intent and startActivityForResult and them implement an onActivityResult in your main activity.
The problem you'll run into, even if you correctly pass you Activity references around is they are not guaranteed to be running at the same time.
Other ways aside from Intents, is to use a class(s) not involved with the Activity. Either a background service or a static variable in a class that extends Application. I rarely use Application classes anymore in favor of services and binding Activities them.
If I use an EventBus in projects, they can send Sticky events, which will hold the data until cleared.

Android uses a messaging mechanism to communicate between its components. This messaging mechnism is essential to Android, so you should use it. And as you already said, the messaging is implemented by Intents. ;-)
If you want something more complex, use an EventBus or implement a your own subscribe/publish mechanism that does what you want.

Use static variable
Example
In your MainActivity define
public static String msg = null;
then in your ChangeText activity assign changed text to it like
MainActivity.msg = edittext.getText().toString();
now in your main activity override the onResume() methode
if(msg != null){
textview.setText(msg);
msg = null;
}

You must LocalBroadCast Manager to do so
Here is the MainActivity which has the TextView which has to updated by another Activity
import android.app.Activity;
import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.os.Bundle;
import android.support.v4.content.LocalBroadcastManager;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.TextView;
public class MainActivity extends Activity {
TextView txt;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
txt=(TextView)findViewById(R.id.txt1);
LocalBroadcastManager.getInstance(this).registerReceiver(mMessageReceiver,
new IntentFilter("custom-event-name"));
}
private BroadcastReceiver mMessageReceiver = new BroadcastReceiver() {
#Override
public void onReceive(Context context, Intent intent) {
String s1= intent.getStringExtra("myString");
getIt(s1);
}
};
#Override
protected void onDestroy() {
// Unregister since the activity is about to be closed.
LocalBroadcastManager.getInstance(this).unregisterReceiver(mMessageReceiver);
super.onDestroy();
}
public void getIt(String s)
{
System.out.println(s);
txt.setText(s);
}
public void go(View view)
{
Intent intent = new Intent(this,WriteText.class);
startActivity(intent);
}
}
And This is the Activity which contains the EditText which updates the TextView in the previous activity
import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.support.v4.content.LocalBroadcastManager;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.EditText;
public class WriteText extends Activity {
EditText ed1;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_write_text);
ed1 = (EditText)findViewById(R.id.textView);
}
public void come(View view){
Intent intent = new Intent("custom-event-name");
intent.putExtra("myString", ed1.getText().toString());
LocalBroadcastManager.getInstance(this).sendBroadcast(intent);
}
}
This Worked for me , Hope it works for you too

onSwipe(int direction) not working

I can't override the onSwipe() method. The error is "The method onSwipe(int) of type Adds must override or implement a supertype method". Can anyone tell me what I did wrong?. I want to navigate between activities using swipe gesture. Is there any other way to do it? If so please explain. Do I have to import any more packages?
package com.mahavega.qcdemo;
import com.mahavega.qcdemo.R;
import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.ImageView;
import android.widget.TextView;
public class Adds extends Activity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.ads);
TextView tv1 = (TextView) findViewById(R.id.textView1);
tv1.setOnClickListener(new OnClickListener() {
#Override
public void onClick(View v) {
// TODO Auto-generated method stub
startActivity(new Intent(Adds.this, Ads2.class));
}
});
ImageView im1 = (ImageView) findViewById(R.id.imageView1);
im1.setOnClickListener(new OnClickListener() {
#Override
public void onClick(View v) {
// TODO Auto-generated method stub
startActivity(new Intent(Adds.this, Real.class));
}
});
}
#Override
public void onSwipe(int direction) {
Intent intent = new Intent();
switch (direction) {
case SimpleGestureFilter.SWIPE_RIGHT:
intent.setClass(this, Ads2.class);
break;
case SimpleGestureFilter.SWIPE_LEFT:
intent.setClass(this, Ads3.class);
break;
}
startActivity(intent);
}
}

your activity should implement SimpleGestureListener to be able to recieve gesture events.
public class Adds extends Activity implements OnGestureListener

Your error reads from the fact that Activity does not have an onSwipe(int) method. So the error is stating that you cannot override a method that has no super method.
Also as #sokie said, check out the OnGestureListener from the link he added.As for swiping gesture used to start new activities,
when swiping left to right, override call onBackPressed (like you are going back) and on swipe right to left start new activity. Although this means you have to create the gesture listener in each of your activities.

Trying to access functions from MainActivity

I am trying to access MainActivity function to my another java class. But i am not able to use these function. Please tell me what else need to be added to get it access.
My code:
Where i am trying to access my MainActivity
package com.example.musicplayer;
**import com.example.musicplayer.MainActivity;**
import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.TextView;
import android.widget.Toast;
public class current_song extends Activity implements OnClickListener{
MainActivity ma = new MainActivity();
protected void onCreate(Bundle icicle) {
Bundle extra = getIntent().getExtras();
super.onCreate(icicle);
setContentView(R.layout.songplay_page);
if(extra != null){
String song_name = extra.getString("song_name");
TextView textchange = (TextView)findViewById(R.id.current_song_name);
textchange.setText(song_name);
textchange.setSelected(true);
}
Button btn_pause = (Button)findViewById(R.id.pause_btn);
btn_pause.setOnClickListener(this);
Button btn_next = (Button)findViewById(R.id.next_btn);
btn_next.setOnClickListener(this);
Button btn_prv = (Button)findViewById(R.id.prv_btn);
btn_prv.setOnClickListener(this);
}
#Override
public void onClick(View v) {
// TODO Auto-generated method stub
Toast.makeText(getApplicationContext(), "In Onclick ()", Toast.LENGTH_SHORT).show();
switch(v.getId())
{
case R.id.pause_btn:
Toast.makeText(getApplicationContext(), "pause", Toast.LENGTH_SHORT).show();
ma.pause();
break;
case R.id.next_btn:
ma.next();
break;
case R.id.prv_btn:
ma.prv();
break;
}
}
}

Make sure that MainActivity has a zero argument constructor and the access specifier for pause , next and prv function is public.

In response to "i have some methods defined by me stop(), next(), pri() i am trying to access these methods when i click on each button. If you think that "creating a separate common class for sharing all methods" can you please show me 1 example bec i don't know how to access a method from 1 activity to another. "
public class myController{
private MyActivity m;
public myController(MyActivity m){
this.m = m;
}
public void stop(){
m.stop;
}
}
In other classes you initialize in the main activity and pass it the controller object so it can call the stop method

ListView: Null pointer exception

Good day. I'm having some issues with my android project specifically listview. I tried searching for other information here in this site, and implemented some of the answers. However, it is still not working.
The error specifically is
NullPointerException at line 76 at MainActivity
Here is the code of my MainActivity
import java.util.ArrayList;
import android.os.Bundle;
import android.app.Activity;
import android.content.Intent;
import android.view.Menu;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.ListView;
public class MainActivity extends Activity {
final ArrayList<String> studentName = new ArrayList<String>();
ArrayAdapter<String> aa;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
ListView myList = (ListView) findViewById(R.id.listName);
aa = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, studentName);
myList.setAdapter(aa);
//droid.R.id.list;
//add
Button bAdd = (Button) findViewById(R.id.addstudent);
bAdd.setOnClickListener(new View.OnClickListener(){
#Override
public void onClick(View v) {
startActivity(new Intent("android.intent.action.ADDSTUDENTS"));
}
});
//edit
Button bEdit = (Button) findViewById(R.id.editstudent);
bEdit.setOnClickListener(new View.OnClickListener(){
#Override
public void onClick(View x) {
startActivity(new Intent("android.intent.action.EDITSTUDENTS"));
}
});
//edit
Button bDelete = (Button) findViewById(R.id.deletestudent);
bDelete.setOnClickListener(new View.OnClickListener(){
#Override
public void onClick(View x) {
startActivity(new Intent("android.intent.action.DELETESTUDENTS"));
}
});
}
public ArrayList<String> getArray(){
return studentName;
}
public void notifyArray(){
aa.notifyDataSetChanged();
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.activity_main, menu);
return true;
}
}
and line 76 by the way is
aa.notifyDataSetChanged();
Here is my code for the AddStudents class
import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
public class AddStudents extends Activity{
#Override
protected void onCreate(Bundle savedInstanceState) {
// TODO Auto-generated method stub
super.onCreate(savedInstanceState);
setContentView(R.layout.add_student);
Button bAddStudents = (Button) findViewById(R.id.add);
final EditText et = (EditText) findViewById(R.id.student_name);
bAddStudents.setOnClickListener(new View.OnClickListener(){
#Override
public void onClick(View v) {
MainActivity as = new MainActivity();
as.getArray().add(et.getText().toString());
as.notifyArray();
finish();
}
});
Button bBack = (Button) findViewById(R.id.backadd);
bBack.setOnClickListener(new View.OnClickListener(){
#Override
public void onClick(View v) {
finish();
}
});
}
}
and the xml part with the list view is
<ListView
android:id="#+id/listName"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_weight="1" >
</ListView>
I hope you can help me cause I want to also learn what my mistakes are. I can add other information if you want.

In your AddStudents class, you're calling notifyArray() right after you instantiated MainActivity. MainActivity.onCreate() will not be called just by instantiating it.
Instantiating your MainActivity there is probably not what you want anyway (because that object will be disposed directly after the onClick handler is done).
What you want instead is to access the existing instance of MainActivity. For that, add a reference to the current instance to a static member of your MainActivity class, e.g.
public class MainActivity extends Activity {
public static MainActivity activity;
#Override
protected void onCreate(Bundle savedInstanceState) {
activity = this;
}
}
Then in your AddStudent class access it via
MainActivity.activity.notifyArray()
This is not the most beautiful way to solve your issue, but it works as long as you can be sure to only have one MainActivity instance. (If not, you could make the array itself static; or create a Singleton wrapper class for it.)

notifyArray() is being called before onCreate.

Try calling getArray().add(et.getText().toString()); and notifyArray(); inside onResume() of MainActivity and NOT from AddStudentActivity( not recommended!)
So onResume() you would ideally want to add a new student to the list, so in your case, you can retrieve the student name using a common sharable object like a hashtable or somethiing similar, make it a singleton, and use it from anywhere in the applciation
The common class may go something like:
class CommonHashtable{
private static Hashtable<String, Object> commonHashtable = null;
public static getInstance(){
if(commonHashtable == null)
commonHashtable = new Hashtable<String, Object>();
return commonHashtable;
}
on getInstance(), it returns a commonHashtable which can be used to store values temporarily!
so, add this on addbutton click event
Hashtable hash = CommonHashtable.getInstance();
hash.put("NEW_STUDENT_NAME", et.getText().toString());
and add this in you onResume() of MainActivity
Hashtable hash = CommonHashtable.getInstance();
Object studentName = (String) hash.get("NEW_STUDENT_NAME");
if(studentName != null){
notifyArray();
}

onClickListener not working that was copied from another working activity

I have created a new activity, added it to my manifest file and copy and pasted code from another fully functioning activity yet my buttons do not work when I click on them. Here is my activity:
import java.util.Calendar;
import android.app.Activity;
import android.app.DatePickerDialog;
import android.app.Dialog;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.DatePicker;
import android.widget.TextView;
public class test extends Activity {
private Button btnChangeDate;
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.salesticketoilui);
mainProgram();
}
public void mainProgram() {
btnChangeDate = (Button) findViewById(R.id.btnChangeDate);
btnChangeDate.setOnClickListener(new OnClickListener() {
public void onClick(View v) {
showDialog(DATE_DIALOG_ID);
} // end onClick
}); // end setOnClickListener
Button buttonExit = (Button)findViewById(R.id.buttonExit);
buttonExit.setOnClickListener(new View.OnClickListener() {
public void onClick(View view) {
exitActivity();
} // end onClick
}); // end OnClickListener
// setup button listener for saving data and exit to main
Button buttonSaveExit = (Button) findViewById(R.id.buttonSaveExit);
buttonSaveExit.setOnClickListener(new View.OnClickListener() {
public void onClick(View view) {
saveExit();
} // end onClick
}); // end OnClickListener
} // end MainProgram ()
public void saveExit() {
// does stuff
}
public void exitActivity () {
// does stuff
}
} // end class
any thoughts?

Based on the code you have shown, it doesn't appear that you ever call the method mainProgram so your click listeners will never actually get setup. Either call mainProgram from onCreate or just put that code directly into onCreate.

I believe the onClickListeners need to go inside of your onCreate method.

Listen to Scott
and looks like your missing the #Override
new View.OnClickListener() {
#Override
public void onClick(View view) {
exitActivity();
} // end onClick
}
Make sure your java settings are to 1.6 to avoid code completion missing this.

I had the same problem copying OnClickListener with ImageButtons from a class to another class, and renaming then with bulk copy/paste.
To make it work, I had to create new buttons in my layout and declare the events manually. Weird!