Question

我在运行时收到空指针异常。我试图在单击图像按钮时从另一个活动调用接口方法。

我已经提到了错误行并发布了相关代码。

堆栈跟踪：

07-24 04:42:38.962    4414-4414/com.ms.ha E/AndroidRuntime﹕ FATAL EXCEPTION: main
    java.lang.NullPointerException
            at com.ms.ha.activity.GridActivity3.onClick(GridActivity3.java:62)
            at android.view.View.performClick(View.java:4240)
            at android.view.View$PerformClick.run(View.java:17721)
            at android.os.Handler.handleCallback(Handler.java:730)
            at android.os.Handler.dispatchMessage(Handler.java:92)
            at android.os.Looper.loop(Looper.java:137)
            at android.app.ActivityThread.main(ActivityThread.java:5103)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:525)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
            at dalvik.system.NativeStart.main(Native Method)

LayoutActivity.java：

public class LayoutActivity extends Activity implements OnClickListener {

ImageButton btn_click;

 private static ItemSelectedListener mListener=null;

 public static void register(ItemSelectedListener listener){
    mListener = listener;
 }

  @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_grid3);

        btn_click = (ImageButton) findViewById(R.id.btn_click);

        btn_click.setOnClickListener(this);
   }
    @Override
    public void onClick(View v) {

        switch (v.getId()) {

            case R.id.btn_click:


             if(mListener!=null){

                mListener.onItemSelected(0, "Home Details");

            }else{
                mListener.onItemSelected(1, "List Details");  --->62nd line

            }
             break;
        }
    }

}

ItemSelectedListener

public interface ItemSelectedListener {

    public void onItemSelected(final int position, final String content);
}

MainActivity.java：

public class MainActivity extends ActionBarActivity implements OnTabChangeListener,ItemSelectedListener {

 private TextView action_bar_hometext;


 @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

}

 @Override
    public void onItemSelected(int position, String content)
    {

        if(position==0)
        {
            action_bar_hometext.setText(content);
            FragmentManager manager = getSupportFragmentManager();
            FragmentTransaction ft = manager.beginTransaction();
            HomeFirstFragment newFragment = new HomeFirstFragment();
            ft.replace(R.id.realtabcontent, newFragment);
            ft.addToBackStack(null);
            ft.commit();
        }
     }

如果我在LayoutActivity类中单击btn_click，我需要执行onClick以从MainActivity调用接口方法。但不幸的是我在运行时遇到错误。

我不知道如何解决这个问题。任何人都可以帮助我。谢谢。

Answer 1

if(mListener!=null){
       mListener.onItemSelected(0, "Home Details");
}else{
       mListener.onItemSelected(1, "List Details");  --->62nd line
}

如果你的监听器不为null你就调用了一些方法，否则你也试图在空引用上调用一些方法

图像按钮单击时出现空指针异常

1 个答案: