Android ImageButton setOnClickListener NullPointerException

Question

我的代码有一个java.lang.NullPointerException错误：

A= (ImageButton) findViewById( R.id.button);
A.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View v) {
        setContentView(R.layout.activity_prof);

    }
});

该应用程序适用于我的手机，三星Galaxy Ace Plus S7500，但它在Nexus 5和三星Galaxy S4的模拟器中崩溃。谁能帮助我？

logcat：

java.lang.RuntimeException: Unable to start activity ComponentInfo{testteam.test/testteam.test.MainActivity}: java.lang.NullPointerException
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2195)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
        at android.app.ActivityThread.access$800(ActivityThread.java:135)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
        at android.os.Handler.dispatchMessage(Handler.java:102)
        at android.os.Looper.loop(Looper.java:136)
        at android.app.ActivityThread.main(ActivityThread.java:5017)
        at java.lang.reflect.Method.invokeNative(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:515)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
        at dalvik.system.NativeStart.main(Native Method)
 Caused by: java.lang.NullPointerException
        at testteam.test.MainActivity.onCreate(MainActivity.java:24)
        at android.app.Activity.performCreate(Activity.java:5231)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2159)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
            at android.app.ActivityThread.access$800(ActivityThread.java:135)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:136)
            at android.app.ActivityThread.main(ActivityThread.java:5017)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:515)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
            at dalvik.system.NativeStart.main(Native Method)

Answer 1

这些错误通常来自查找错误的观点。请仔细检查您的xml布局，确保xml中有一个名为ImageButton的{​​{1}}。

似乎此button不在您当前的视图中。可能是因为您在ImageButton

中设置setContentView之前未调用onClickListener方法