How to implement OnClickListener on Android
48,477
Try this:
public class MainActivity extends Activity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
if (savedInstanceState == null) {
getFragmentManager().beginTransaction()
.add(R.id.container, new PlaceholderFragment()).commit();
}
//Button button = (Button)findViewById(R.id.try_button);
//button.setOnClickListener(this);
}
/**
public void onClick(View v) {
}
*/
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.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();
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
/**
* A placeholder fragment containing a simple view.
*/
public static class PlaceholderFragment extends Fragment implements OnClickListener {
public PlaceholderFragment() {
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_main, container,
false);
Button button = (Button) rootView.findViewById(R.id.try_button);
button.setOnClickListener(this);
return rootView;
}
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
Toast.makeText(getActivity(), "I'm clicked!", Toast.LENGTH_SHORT).show();
}
}
}
Author by
Bamqf
Updated on December 05, 2020Comments
-
Bamqf over 3 years
I learn from
http://developer.android.com/reference/android/widget/Button.html
that "instead of applying an OnClickListener to the button in your activity, you can assign a method to your button in the XML layout, using the android:onClick attribute."
However, I can only get it done with the XML approach, my Listener approach, specified by the following, leads to app crash.
In my fragment_main.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:paddingBottom="@dimen/activity_vertical_margin" android:paddingLeft="@dimen/activity_horizontal_margin" android:paddingRight="@dimen/activity_horizontal_margin" android:paddingTop="@dimen/activity_vertical_margin" tools:context="com.example.myapp.MainActivity$PlaceholderFragment" > <TextView android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="@string/hello_world" /> <Button android:id="@+id/try_button" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text = "TryButton" android:onClick="onClick" /> </RelativeLayout>
In my activity_main.xml:
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:tools="http://schemas.android.com/tools" android:id="@+id/container" android:layout_width="match_parent" android:layout_height="match_parent" tools:context="com.example.myapp.MainActivity" tools:ignore="MergeRootFrame"> </FrameLayout>
And in my MainActivity.java:
public class MainActivity extends Activity implements OnClickListener{ @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); if (savedInstanceState == null) { getFragmentManager().beginTransaction() .add(R.id.container, new PlaceholderFragment()).commit(); } Button button = (Button)findViewById(R.id.try_button); button.setOnClickListener(this); } public void onClick(View v) { Toast.makeText(getApplicationContext(), "I'm clicked!", Toast.LENGTH_SHORT).show();; } @Override public boolean onCreateOptionsMenu(Menu menu) { // Inflate the menu; this adds items to the action bar if it is present. getMenuInflater().inflate(R.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(); if (id == R.id.action_settings) { return true; } return super.onOptionsItemSelected(item); } /** * A placeholder fragment containing a simple view. */ public static class PlaceholderFragment extends Fragment { public PlaceholderFragment() { } @Override public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { View rootView = inflater.inflate(R.layout.fragment_main, container, false); return rootView; } }
}
The LogCat says:
05-20 19:56:17.604: E/MoreInfoHPW_ViewGroup(566): Parent view is not a TextView 05-20 19:56:17.649: D/AndroidRuntime(566): Shutting down VM 05-20 19:56:17.649: W/dalvikvm(566): threadid=1: thread exiting with uncaught exception (group=0x4194ec08) 05-20 19:56:17.654: E/AndroidRuntime(566): FATAL EXCEPTION: main 05-20 19:56:17.654: E/AndroidRuntime(566): Process: com.example.myapp, PID: 566 05-20 19:56:17.654: E/AndroidRuntime(566): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.myapp/com.example.myapp.MainActivity}: java.lang.NullPointerException 05-20 19:56:17.654: E/AndroidRuntime(566): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2328) 05-20 19:56:17.654: E/AndroidRuntime(566): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2386) 05-20 19:56:17.654: E/AndroidRuntime(566): at android.app.ActivityThread.access$900(ActivityThread.java:169) 05-20 19:56:17.654: E/AndroidRuntime(566): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1277) 05-20 19:56:17.654: E/AndroidRuntime(566): at android.os.Handler.dispatchMessage(Handler.java:102) 05-20 19:56:17.654: E/AndroidRuntime(566): at android.os.Looper.loop(Looper.java:136) 05-20 19:56:17.654: E/AndroidRuntime(566): at android.app.ActivityThread.main(ActivityThread.java:5476) 05-20 19:56:17.654: E/AndroidRuntime(566): at java.lang.reflect.Method.invokeNative(Native Method) 05-20 19:56:17.654: E/AndroidRuntime(566): at java.lang.reflect.Method.invoke(Method.java:515) 05-20 19:56:17.654: E/AndroidRuntime(566): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1268) 05-20 19:56:17.654: E/AndroidRuntime(566): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1084) 05-20 19:56:17.654: E/AndroidRuntime(566): at dalvik.system.NativeStart.main(Native Method) 05-20 19:56:17.654: E/AndroidRuntime(566): Caused by: java.lang.NullPointerException 05-20 19:56:17.654: E/AndroidRuntime(566): at com.example.myapp.MainActivity.onCreate(MainActivity.java:29) 05-20 19:56:17.654: E/AndroidRuntime(566): at android.app.Activity.performCreate(Activity.java:5473) 05-20 19:56:17.654: E/AndroidRuntime(566): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1093) 05-20 19:56:17.654: E/AndroidRuntime(566): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2292) 05-20 19:56:17.654: E/AndroidRuntime(566): ... 11 more
I'm using latest Eclipse ADT v22.6.2 on Windows 7, running on Samsung Galaxy Note 10.1 2014.
What's wrong with my code?
-
Bamqf almost 10 yearsThat would be the xml-only approach, I know it works. But I need to learn the Listener approach.
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Bamqf almost 10 yearsThank you for your answer, but I tried and got similar crash log(with and without the onClick xml attribute). I've edited my post with the complete contents of my files, maybe it would help.
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dorukayhan almost 8 yearsYou could make this answer better by explaining how it works.