Android应用程式已停止运作-eclipse

Question

I have been tried to build my first Android Application. Every time I open the application in the emulator, I just get a message that says test has stopped working. It must be something simple. Hope you can help me.

04-06 15:43:47.806: W/dalvikvm(4275): threadid=1: thread exiting with uncaught exception (group=0xa614d908)

04-06 15:43:47.826: E/AndroidRuntime(4275): FATAL EXCEPTION: main

04-06 15:43:47.826: E/AndroidRuntime(4275): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.test/com.test.MainActivity}: java.lang.NullPointerException

04-06 15:43:47.826: E/AndroidRuntime(4275): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180)

04-06 15:43:47.826: E/AndroidRuntime(4275): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)

04-06 15:43:47.826: E/AndroidRuntime(4275): at android.app.ActivityThread.access$600(ActivityThread.java:141)

04-06 15:43:47.826: E/AndroidRuntime(4275): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)

04-06 15:43:47.826: E/AndroidRuntime(4275): at android.os.Handler.dispatchMessage(Handler.java:99)

04-06 15:43:47.826: E/AndroidRuntime(4275): at android.os.Looper.loop(Looper.java:137)

04-06 15:43:47.826: E/AndroidRuntime(4275): at android.app.ActivityThread.main(ActivityThread.java:5041)

04-06 15:43:47.826: E/AndroidRuntime(4275): at java.lang.reflect.Method.invokeNative(Native Method)

04-06 15:43:47.826: E/AndroidRuntime(4275): at java.lang.reflect.Method.invoke(Method.java:511)

04-06 15:43:47.826: E/AndroidRuntime(4275): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)

04-06 15:43:47.826: E/AndroidRuntime(4275): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)

04-06 15:43:47.826: E/AndroidRuntime(4275): at dalvik.system.NativeStart.main(Native Method)

04-06 15:43:47.826: E/AndroidRuntime(4275): Caused by: java.lang.NullPointerException

04-06 15:43:47.826: E/AndroidRuntime(4275): at com.test.MainActivity.onCreate(MainActivity.java:30)

04-06 15:43:47.826: E/AndroidRuntime(4275): at android.app.Activity.performCreate(Activity.java:5104)

04-06 15:43:47.826: E/AndroidRuntime(4275): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080)

04-06 15:43:47.826: E/AndroidRuntime(4275): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144)

04-06 15:43:47.826: E/AndroidRuntime(4275): ... 11 more

Above is the log file

public class Main extends ActionBarActivity {

    int counter ;
        Button add, sub ;
        TextView display;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
          super.onCreate(savedInstanceState);
      setContentView(R.layout.activity_main);
      counter = 0;
          add = (Button) findViewById (R.id.bAdd);
          sub = (Button) findViewById (R.id.bsub);
          display = (TextView) findViewById(R.id.tvDisplay);
          add.setOnClickListener(new  View.OnClickListener() {

            @Override
            public void onClick(View v) {
                // TODO Auto-generated method stub
                counter++;
                display.setText("Your total is " + counter);

            }
        });

          sub.setOnClickListener(new  View.OnClickListener() {

            @Override
            public void onClick(View v) {
                // TODO Auto-generated method stub
                counter --;
                display.setText("Your total is " + counter);
            }
        });


        if (savedInstanceState == null) {
            getSupportFragmentManager().beginTransaction()
               .add(R.id.container, new PlaceholderFragment()).commit();
        }
    }

        @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;
        }
    }

}

Above is the Main class

<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.test.MainActivity$PlaceholderFragment" >

   <TextView
        android:id="@+id/tvDisplay"
        android:layout_width="wrap_content"
        android:layout_height="match_parent"
        android:layout_alignLeft="@+id/bsub"
        android:layout_alignParentBottom="true"
        android:layout_below="@+id/bsub"
        android:gravity="center"
        android:text="Your total is 0"
        android:textSize="45dp" />

    <Button
        android:id="@+id/badd"
        android:layout_width="250dp"
        android:layout_height="wrap_content"
        android:layout_alignParentLeft="true"
        android:layout_alignParentTop="true"
        android:layout_marginLeft="16dp"
        android:layout_marginTop="78dp"
        android:gravity="center"
        android:text="Add one"
        android:textSize="20dp" />

    <Button
        android:id="@+id/bsub"
        android:layout_width="250dp"
        android:layout_height="wrap_content"
        android:layout_toRightOf="@+id/badd"
        android:layout_centerHorizontal="true"
        android:gravity="center"
        android:text="Subtract one"
        android:textSize="20dp" />



</RelativeLayout>

Above is the fragment_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.Hello.firstapp.Main"
    tools:ignore="MergeRootFrame" />

ABove is the activity_main.xml

Answer 1

Instead of onCreate() move all ur initialization into onCreateView() as those buttons and textview is in ur fragment_main.xml thats why u got NPE as those buttons and textview is not the part of activity_main.xml .

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,Bundle savedInstanceState) {
            View rootView = inflater.inflate(R.layout.fragment_main, container, false);
counter = 0;
add = (Button) rootView.findViewById (R.id.bAdd);
sub = (Button) rootView.findViewById (R.id.bsub);
display = (TextView) rootView.findViewById(R.id.tvDisplay);
add.setOnClickListener(new  View.OnClickListener() {

 @Override
 public void onClick(View v) {
 // TODO Auto-generated method stub
  counter++;
   display.setText("Your total is " + counter);

    }
   });

  sub.setOnClickListener(new  View.OnClickListener() {

   @Override
   public void onClick(View v) {
   // TODO Auto-generated method stub
   counter --;
   display.setText("Your total is " + counter);
   }
  });
 return rootView;
}

Answer 2

I see your issue. activity_main.xml contains a frame layout, in which your fragment_main.xml is inflated. The thing is that, both add and sub are null, as you're looking for them in the wrong layout. Thus, call the FragmentTransaction first and move all your button code to the onCreateView of the PlaceHolderFragment and your issue should be fixed. I have provided the fixed code, all you have to do is copy it and remove the button code from onCreate (...)

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,Bundle savedInstanceState) {

    View rootView = inflater.inflate(R.layout.fragment_main, container, false);

    counter = 0;

    add = (Button) rootView.findViewById (R.id.bAdd);
    sub = (Button) rootView.findViewById (R.id.bsub);
    display = (TextView) rootView.findViewById(R.id.tvDisplay);

    add.setOnClickListener(new  View.OnClickListener() {

        @Override
        public void onClick(View v) {
        // TODO Auto-generated method stub
            counter++;
            display.setText("Your total is " + counter);
        }
    });

    sub.setOnClickListener(new  View.OnClickListener() {

        @Override
        public void onClick(View v) {
        // TODO Auto-generated method stub
             counter --;
             display.setText("Your total is " + counter);
        }
    });

    return rootView;
}

Answer 3

Most likely

add = (Button) findViewById (R.id.bAdd);

returns null , because the element is not defined on your activity_main view.