Question

我在xml中添加了一个图像和一个按钮，如下所示

 <Button
        android:id="@+id/btnChangeImage"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Change Image" />

    <ImageView
        android:id="@+id/imageView1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:src="@drawable/buttonplayicon" />

点击按钮我要更改图像。下面是按钮

的main_activity onclick功能

public void addListenerOnButton() {

    image = (ImageView) findViewById(R.id.imageView1);

    button = (Button) findViewById(R.id.btnChangeImage);
    button.setOnClickListener(new OnClickListener() {

    @Override
    public void onClick(View v) {
        image.setImageResource(R.drawable.player_pause);

        }
    });
}

如果我添加

button.setOnClickListener(new OnClickListener() {

    @Override
    public void onClick(View v) {
        image.setImageResource(R.drawable.player_pause);

    }
});

在函数中，我收到消息“遗憾的应用程序停止了”

对此有任何想法吗？

编辑1

要查看logcat，如果我关注（在eclipse：Window＆gt; show view＆gt; other＆gt; android＆gt; Logcat）步骤我得到Logcat（已弃用）

编辑2 logcat：

06-12 13:37:43.006: E/AndroidRuntime(3159): Caused by: java.lang.NullPointerException
06-12 13:37:43.006: E/AndroidRuntime(3159):     at com.example.play_audio_app.MainActivity.addListenerOnButton(MainActivity.java:38)
06-12 13:37:43.006: E/AndroidRuntime(3159):     at com.example.play_audio_app.MainActivity.onCreate(MainActivity.java:30)
06-12 13:37:43.006: E/AndroidRuntime(3159):     at android.app.Activity.performCreate(Activity.java:5231)
06-12 13:37:43.006: E/AndroidRuntime(3159):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
06-12 13:37:43.006: E/AndroidRuntime(3159):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2159)
06-12 13:37:43.006: E/AndroidRuntime(3159):     ... 11 more
06-12 13:38:41.816: D/AndroidRuntime(3304): Shutting down VM
06-12 13:38:41.816: W/dalvikvm(3304): threadid=1: thread exiting with uncaught exception (group=0x4164eba8)
06-12 13:38:41.816: E/AndroidRuntime(3304): FATAL EXCEPTION: main
06-12 13:38:41.816: E/AndroidRuntime(3304): Process: com.example.play_audio_app, PID: 3304
06-12 13:38:41.816: E/AndroidRuntime(3304): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.play_audio_app/com.example.play_audio_app.MainActivity}: java.lang.NullPointerException
06-12 13:38:41.816: E/AndroidRuntime(3304):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2195)
06-12 13:38:41.816: E/AndroidRuntime(3304):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
06-12 13:38:41.816: E/AndroidRuntime(3304):     at android.app.ActivityThread.access$800(ActivityThread.java:135)
06-12 13:38:41.816: E/AndroidRuntime(3304):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
06-12 13:38:41.816: E/AndroidRuntime(3304):     at android.os.Handler.dispatchMessage(Handler.java:102)
06-12 13:38:41.816: E/AndroidRuntime(3304):     at android.os.Looper.loop(Looper.java:136)
06-12 13:38:41.816: E/AndroidRuntime(3304):     at android.app.ActivityThread.main(ActivityThread.java:5017)
06-12 13:38:41.816: E/AndroidRuntime(3304):     at java.lang.reflect.Method.invokeNative(Native Method)
06-12 13:38:41.816: E/AndroidRuntime(3304):     at java.lang.reflect.Method.invoke(Method.java:515)
06-12 13:38:41.816: E/AndroidRuntime(3304):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
06-12 13:38:41.816: E/AndroidRuntime(3304):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
06-12 13:38:41.816: E/AndroidRuntime(3304):     at dalvik.system.NativeStart.main(Native Method)
06-12 13:38:41.816: E/AndroidRuntime(3304): Caused by: java.lang.NullPointerException
06-12 13:38:41.816: E/AndroidRuntime(3304):     at com.example.play_audio_app.MainActivity.addListenerOnButton(MainActivity.java:38)
06-12 13:38:41.816: E/AndroidRuntime(3304):     at com.example.play_audio_app.MainActivity.onCreate(MainActivity.java:30)
06-12 13:38:41.816: E/AndroidRuntime(3304):     at android.app.Activity.performCreate(Activity.java:5231)
06-12 13:38:41.816: E/AndroidRuntime(3304):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
06-12 13:38:41.816: E/AndroidRuntime(3304):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2159)
06-12 13:38:41.816: E/AndroidRuntime(3304):     ... 11 more

编辑3

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

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

        addListenerOnButton();
    }

Answer 1

只需在XML中设置onClick，就容易多了。

android:onClick="whatever"

然后在你的班上，

public void whatever(View v) {
    // Do your stuff
}

你不需要这一切：

button.setOnClickListener(new OnClickListener() {

    @Override
    public void onClick(View v) {
        image.setImageResource(R.drawable.player_pause);

        }
    });

button.setOnClickListener不起作用

1 个答案: