I am really frustrated after updating my ADT. Previously a new Android project only include activity_main.xml
file in which we add elements of our interface. Now after updating the ADT whenever I create a new android project it creates a fragment_main.xml
along with activity_main.xml
file. What is this fragment_main.xml
? Also MainActivity.class
includes some extra code like a class named PlaceholderFragment
and some other weird stuff.
Now the main problem is I can't even add onClickListener
for a button in fragment_main.xml
.
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.cameraproject.MainActivity$PlaceholderFragment" >
<Button
android:id="@+id/button1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentTop="true"
android:layout_centerHorizontal="true"
android:layout_marginTop="188dp"
android:text="Button" />
</RelativeLayout>
MainActivity.class :
package com.example.cameraproject;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v7.app.ActionBarActivity;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.Toast;
public class MainActivity extends ActionBarActivity implements OnClickListener {
public static Button b;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
if (savedInstanceState == null) {
getSupportFragmentManager().beginTransaction().add(R.id.container, new PlaceholderFragment()).commit();
}
b = (Button) findViewById(R.id.button1);
b.setOnClickListener(this);
}
@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;
}
}
@Override
public void onClick(View v) {
switch (v.getId()) {
case R.id.button1:
Toast.makeText(this, "Its working", Toast.LENGTH_SHORT).show();
break;
}
}
}
Error log :
04-22 11:16:54.186: E/AndroidRuntime(17336): FATAL EXCEPTION: main
04-22 11:16:54.186: E/AndroidRuntime(17336): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.cameraproject/com.example.cameraproject.MainActivity}: java.lang.NullPointerException
04-22 11:16:54.186: E/AndroidRuntime(17336): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2308)
04-22 11:16:54.186: E/AndroidRuntime(17336): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2362)
04-22 11:16:54.186: E/AndroidRuntime(17336): at android.app.ActivityThread.access$700(ActivityThread.java:168)
04-22 11:16:54.186: E/AndroidRuntime(17336): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1329)
04-22 11:16:54.186: E/AndroidRuntime(17336): at android.os.Handler.dispatchMessage(Handler.java:99)
04-22 11:16:54.186: E/AndroidRuntime(17336): at android.os.Looper.loop(Looper.java:137)
04-22 11:16:54.186: E/AndroidRuntime(17336): at android.app.ActivityThread.main(ActivityThread.java:5493)
04-22 11:16:54.186: E/AndroidRuntime(17336): at java.lang.reflect.Method.invokeNative(Native Method)
04-22 11:16:54.186: E/AndroidRuntime(17336): at java.lang.reflect.Method.invoke(Method.java:525)
04-22 11:16:54.186: E/AndroidRuntime(17336): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1209)
04-22 11:16:54.186: E/AndroidRuntime(17336): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1025)
04-22 11:16:54.186: E/AndroidRuntime(17336): at dalvik.system.NativeStart.main(Native Method)
04-22 11:16:54.186: E/AndroidRuntime(17336): Caused by: java.lang.NullPointerException
04-22 11:16:54.186: E/AndroidRuntime(17336): at com.example.cameraproject.MainActivity.onCreate(MainActivity.java:28)
04-22 11:16:54.186: E/AndroidRuntime(17336): at android.app.Activity.performCreate(Activity.java:5372)
04-22 11:16:54.186: E/AndroidRuntime(17336): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1104)
04-22 11:16:54.186: E/AndroidRuntime(17336): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2270)
Try this..
Your Button is belongs to fragment_main.xml
So you have to initialize it in PlaceholderFragment
public static class PlaceholderFragment extends Fragment {
public PlaceholderFragment() {
}
Button b;
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_main, container, false);
b = (Button) findViewById(R.id.button1);
b.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
Toast.makeText(getActivity(), "Its working", Toast.LENGTH_SHORT).show();
}
});
return rootView;
}
}
You have set the layout file as activity_main.xml
..But you have added the button in fragment_main.xml
..That is why the null pointer exception is raised..
Replace this
setContentView(R.layout.activity_main);
with
setContentView(R.layout.fragment_main);
This is the most simple solution...
OR
Copy the whole contents in fragment_main.xml
to activity_main.xml
...
Hope it helps..
Reaplace this line
setContentView(R.layout.activity_main);
by setContentView(R.layout.fragment_main);
Your Button belongs to fragment's layout not your activiti's layout. Hence, remove button view initialization code from your activitie's onCreate() and add,
View rootView = inflater.inflate(R.layout.fragment_main, container, false); Button b = (Button) rootView.findViewById(R.id.button1);
in onCreateView() of your PlaceholderFragment .
The technical post webpages of this site follow the CC BY-SA 4.0 protocol. If you need to reprint, please indicate the site URL or the original address.Any question please contact:yoyou2525@163.com.