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我得到一个空指针异常gridView.setOnItemClickListener(new OnItemClickListener()。我该如何初始化它？这是在 MainActivity 的 `onCreate 方法中。

 GridView gridView = (GridView)findViewById(R.id.grid_view);

 gridView.setOnItemClickListener(new OnItemClickListener() {

        @Override
        public void onItemClick(AdapterView<?> parent, View v, int position,
                long id) {
            // sending image id to FullScreenActivity
            Intent i = new Intent(getApplicationContext(), FullImage2.class);
            // passing array index
            i.putExtra("id", position);
            startActivity(i);       
        }
    });

那是日志：

03-30 11:51:31.993: E/AndroidRuntime(879): FATAL EXCEPTION: main
03-30 11:51:31.993: E/AndroidRuntime(879): java.lang.RuntimeException: Unable to start activity ComponentInfo{ie.gmit.gmitapp/ie.gmit.gmitapp.MainActivity}: java.lang.NullPointerException
03-30 11:51:31.993: E/AndroidRuntime(879):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180)
03-30 11:51:31.993: E/AndroidRuntime(879):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
03-30 11:51:31.993: E/AndroidRuntime(879):  at android.app.ActivityThread.access$600(ActivityThread.java:141)
03-30 11:51:31.993: E/AndroidRuntime(879):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
03-30 11:51:31.993: E/AndroidRuntime(879):  at android.os.Handler.dispatchMessage(Handler.java:99)
03-30 11:51:31.993: E/AndroidRuntime(879):  at android.os.Looper.loop(Looper.java:137)
03-30 11:51:31.993: E/AndroidRuntime(879):  at android.app.ActivityThread.main(ActivityThread.java:5039)
03-30 11:51:31.993: E/AndroidRuntime(879):  at java.lang.reflect.Method.invokeNative(Native Method)
03-30 11:51:31.993: E/AndroidRuntime(879):  at java.lang.reflect.Method.invoke(Method.java:511)
03-30 11:51:31.993: E/AndroidRuntime(879):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
03-30 11:51:31.993: E/AndroidRuntime(879):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
03-30 11:51:31.993: E/AndroidRuntime(879):  at dalvik.system.NativeStart.main(Native Method)
03-30 11:51:31.993: E/AndroidRuntime(879): Caused by: java.lang.NullPointerException
03-30 11:51:31.993: E/AndroidRuntime(879):  at ie.gmit.gmitapp.MainActivity.onCreate(MainActivity.java:184)
03-30 11:51:31.993: E/AndroidRuntime(879):  at android.app.Activity.performCreate(Activity.java:5104)
03-30 11:51:31.993: E/AndroidRuntime(879):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080)
03-30 11:51:31.993: E/AndroidRuntime(879):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144)

FullImage2.类：

public class FullImage2 extends Activity {
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_full_image);
    //get intent data
    Intent i = getIntent();
    // selected image id
    int position = i.getExtras().getInt("id");
    ImageAdapter imageAdapter = new ImageAdapter(this);
    ImageView imageView = (ImageView)findViewById(R.id.full_image_view);
    imageView.setImageResource(imageAdapter.mThumbIds[position]);

    //implement up navigation
    getActionBar().setDisplayHomeAsUpEnabled(true);

}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.full_image, menu);
    return true;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // TODO Auto-generated method stub
    switch (item.getItemId()){
    case android.R.id.home:
        //this is called when the home up button is pressed in the action bar
        Intent parentActivityIntent = new Intent(this, MainActivity.class);
        parentActivityIntent.addFlags(
        Intent.FLAG_ACTIVITY_CLEAR_TOP |
        Intent.FLAG_ACTIVITY_NEW_TASK);
        startActivity(parentActivityIntent);
        finish();
        return true;
    }
    return super.onOptionsItemSelected(item);
}

}

第 184 行是：

 gridView.setOnItemClickListener(new OnItemClickListener() {
4

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