当我实现onclicklistener时，Android应用程序崩溃了

Question

我在尝试实现onClickListener时总是收到错误。

有我的代码

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

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

        @Override
        public void onClick(View v) {
            // TODO Auto-generated method stub

        }
    });     

这是我的XML代码：      logcat的

06-07 02:54:05.901: E/AndroidRuntime(19667): FATAL EXCEPTION: main
06-07 02:54:05.901: E/AndroidRuntime(19667): Process: com.gonzalo.ejemplo, PID: 19667
06-07 02:54:05.901: E/AndroidRuntime(19667): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.gonzalo.ejemplo/com.gonzalo.ejemplo.MainActivity}: java.lang.NullPointerException
06-07 02:54:05.901: E/AndroidRuntime(19667):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2305)
06-07 02:54:05.901: E/AndroidRuntime(19667):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2363)
06-07 02:54:05.901: E/AndroidRuntime(19667):    at android.app.ActivityThread.access$900(ActivityThread.java:161)
06-07 02:54:05.901: E/AndroidRuntime(19667):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1265)
06-07 02:54:05.901: E/AndroidRuntime(19667):    at android.os.Handler.dispatchMessage(Handler.java:102)
06-07 02:54:05.901: E/AndroidRuntime(19667):    at android.os.Looper.loop(Looper.java:157)
06-07 02:54:05.901: E/AndroidRuntime(19667):    at android.app.ActivityThread.main(ActivityThread.java:5356)
06-07 02:54:05.901: E/AndroidRuntime(19667):    at java.lang.reflect.Method.invokeNative(Native Method)
06-07 02:54:05.901: E/AndroidRuntime(19667):    at java.lang.reflect.Method.invoke(Method.java:515)
06-07 02:54:05.901: E/AndroidRuntime(19667):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1265)
06-07 02:54:05.901: E/AndroidRuntime(19667):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1081)
06-07 02:54:05.901: E/AndroidRuntime(19667):    at dalvik.system.NativeStart.main(Native Method)
06-07 02:54:05.901: E/AndroidRuntime(19667): Caused by: java.lang.NullPointerException
06-07 02:54:05.901: E/AndroidRuntime(19667):    at com.gonzalo.ejemplo.MainActivity.onCreate(MainActivity.java:27)
06-07 02:54:05.901: E/AndroidRuntime(19667):    at android.app.Activity.performCreate(Activity.java:5426)
06-07 02:54:05.901: E/AndroidRuntime(19667):    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1105)
06-07 02:54:05.901: E/AndroidRuntime(19667):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2269)
06-07 02:54:05.901: E/AndroidRuntime(19667):    ... 11 more
06-07 02:59:05.974: I/Process(19667): Sending signal. PID: 19667 SIG: 9

所以..任何想法我该如何解决？

由于

Answer 1

findViewById可能返回null。确保布局中有一个带有android:id="@+id/btn_submit"的按钮。

Answer 2

这个变量可能是问题。

Button btn_submit = (Button) findViewById(R.id.btn_submit);

签入activity_main.xml如果存在btn_submit，可能还有其他名称。