setOnClickListener使我的应用程序崩溃

时间：2014-05-19 18:25:51

标签： android eclipse onclicklistener buttonclick

我知道这个问题已被多次询问，但其他答案都没有帮助我。当我注释掉setOnClickListener时，我的代码工作正常。

所以，这是我的主要活动...... 

public class StartingPoint extends ActionBarActivity {

int ctr = 0;
Button add, sub;
TextView display;

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

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

    //find views
    display = (TextView) findViewById(R.id.tvTotal);
    add = (Button)this. findViewById(R.id.bAdd);
    sub = (Button)this. findViewById(R.id.bSub);

    //click listeners
    OnClickListener lis = new OnClickListener() {
        @Override
        public void onClick(View v) {
            // TODO Auto-generated method stub
            ctr++;
            display.setText("The total is " + ctr);
        }
    };
    add.setOnClickListener(lis);

    /**sub.setOnClickListener(new View.OnClickListener() {

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

}
@Override
public boolean onCreateOptionsMenu(Menu menu) {...}

@Override
public boolean onOptionsItemSelected(MenuItem item) {...}

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_starting_point,
                container, false);
        return rootView;
    }
}

}

add.setOnClickListener（lis）;使应用程序崩溃。

这是fragment_starting_point.xml ... 

<LinearLayout 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:orientation="vertical" >

<TextView
    android:id="@+id/tvTotal"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:text="The total is 0"
    android:layout_gravity="top"
    android:gravity="center"
    android:textSize="30sp"
    android:textColor="@color/red"
/>

<Button
    android:id="@+id/bAdd"
    android:layout_width="150sp"
    android:layout_height="wrap_content"
    android:text="Add 1"
    android:textSize="20sp"
    android:layout_gravity="center"
    android:gravity="center"
    />

<Button
    android:id="@+id/bSub"
    android:layout_width="150sp"
    android:layout_height="wrap_content"
    android:text="Subtract 1"
    android:textSize="20sp"
    android:layout_gravity="center"
    android:gravity="center"
/>

这就是logCat所说的...... 

05-19 23:23:09.700: D/CLIPBOARD(16417): Hide Clipboard dialog at Starting input:         finished by someone else... !
05-19 23:23:34.085: I/dalvikvm(16518): Could not find method     android.widget.LinearLayout$LayoutParams.<init>, referenced from method     android.support.v7.internal.view.menu.ActionMenuView$LayoutParams.<init>
05-19 23:23:34.085: W/dalvikvm(16518): VFY: unable to resolve direct method 8208:    Landroid/widget/LinearLayout$LayoutParams;.<init> (Landroid/widget/LinearLayout$LayoutParams;)V
05-19 23:23:34.085: D/dalvikvm(16518): VFY: replacing opcode 0x70 at 0x0000
05-19 23:23:34.115: D/CLIPBOARD(16518): Hide Clipboard dialog at Starting input: finished by someone else... !
05-19 23:23:37.760: D/CLIPBOARD(16518): Hide Clipboard dialog at Starting input: finished by someone else... !
05-19 23:28:52.000: D/AndroidRuntime(16834): Shutting down VM
05-19 23:28:52.000: W/dalvikvm(16834): threadid=1: thread exiting with uncaught exception (group=0x40192760)
05-19 23:28:52.000: E/AndroidRuntime(16834): FATAL EXCEPTION: main
05-19 23:28:52.000: E/AndroidRuntime(16834): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example2.mysecondapp/com.example2.mysecondapp.StartingPoint}: java.lang.NullPointerException
05-19 23:28:52.000: E/AndroidRuntime(16834):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1815)
05-19 23:28:52.000: E/AndroidRuntime(16834):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1831)
05-19 23:28:52.000: E/AndroidRuntime(16834):    at android.app.ActivityThread.access$500(ActivityThread.java:122)
05-19 23:28:52.000: E/AndroidRuntime(16834):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1024)
05-19 23:28:52.000: E/AndroidRuntime(16834):    at android.os.Handler.dispatchMessage(Handler.java:99)
05-19 23:28:52.000: E/AndroidRuntime(16834):    at android.os.Looper.loop(Looper.java:132)
05-19 23:28:52.000: E/AndroidRuntime(16834):    at android.app.ActivityThread.main(ActivityThread.java:4123)
05-19 23:28:52.000: E/AndroidRuntime(16834):    at java.lang.reflect.Method.invokeNative(Native Method)
05-19 23:28:52.000: E/AndroidRuntime(16834):    at java.lang.reflect.Method.invoke(Method.java:491)
05-19 23:28:52.000: E/AndroidRuntime(16834):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:844)
05-19 23:28:52.000: E/AndroidRuntime(16834):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:602)
05-19 23:28:52.000: E/AndroidRuntime(16834):    at dalvik.system.NativeStart.main(Native Method)
05-19 23:28:52.000: E/AndroidRuntime(16834): Caused by: java.lang.NullPointerException
05-19 23:28:52.000: E/AndroidRuntime(16834):    at com.example2.mysecondapp.StartingPoint.onCreate(StartingPoint.java:47)
05-19 23:28:52.000: E/AndroidRuntime(16834):    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1050)
05-19 23:28:52.000: E/AndroidRuntime(16834):    at     android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1779)
05-19 23:28:52.000: E/AndroidRuntime(16834):    ... 11 more
05-19 23:28:59.720: I/Process(16834): Sending signal. PID: 16834 SIG: 9

我不知道到底需要什么，所以我发布了我认为相关的所有内容，我还是新手。我真的很感激任何帮助。

2 个答案:

答案 0 :(得分：1)

Fragment的布局包含Button，其内容为R.id.bAdd，Activity的布局不包含add = (Button)this.findViewById(R.id.bAdd); 。这是您的错误来源，这一行：

Button

在Activity的布局中找不到OnClickListener，因此它返回null。之后，当您尝试设置NullPointerException时，您会获得Buttons。

您需要做的是将与Fragment等的所有互动转移到它不属于Activity的{​​{1}}中，因为它不属于Activity onCreateView()的布局。覆盖Fragment中的Views方法并在那里夸大您的布局，然后像这样查找@Override public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { View view = inflater.inflate(R.layout.fragment_starting_point, container, false); this.add = (Button) view.findViewById(R.id.bAdd); return view; } ：

OnClickListener

然后，您可以在onViewCreated()中添加@Override public void onViewCreated(View view, Bundle savedInstanceState) { super.onViewCreated(view, savedInstanceState); this.add.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { ... } }); } ：

{{1}}

答案 1 :(得分：0)

这是因为findViewById()在activity_main布局中搜索，而按钮位于片段的布局fragment_main中。

在片段的onCreateView()方法中移动该段代码：

//...

View rootView = inflater.inflate(R.layout.fragment_main, container, false);
Button buttonClick = (Button)rootView.findViewById(R.id.button);
buttonClick.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View view) {
        onButtonClick((Button) view);
    }
});

请注意，现在您可以通过rootView view访问它：

Button buttonClick = (Button)rootView.findViewById(R.id.button);

否则你会再次NullPointerException。

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