尝试导航到上一个活动时意图崩溃

Question

基本上，我不知道为什么，但是当我尝试从一个活动转到上一个活动（使用ym后退按钮）时，intent为null，因此为null指针异常。

我这样做的目的是：

 Intent intent = new Intent(Puzzle_Activity.this, Play_Activity.class );
    startActivity(intent);

据我所知，该代码没有任何问题。 但是logcat给了我

 04-24 19:23:15.074: E/AndroidRuntime(829): FATAL EXCEPTION: main
04-24 19:23:15.074: E/AndroidRuntime(829): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.angrywordsearch/com.example.angrywordsearch.Play_Activity}: java.lang.NullPointerException
04-24 19:23:15.074: E/AndroidRuntime(829):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2059)
04-24 19:23:15.074: E/AndroidRuntime(829):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2084)
04-24 19:23:15.074: E/AndroidRuntime(829):  at android.app.ActivityThread.access$600(ActivityThread.java:130)
04-24 19:23:15.074: E/AndroidRuntime(829):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195)
04-24 19:23:15.074: E/AndroidRuntime(829):  at android.os.Handler.dispatchMessage(Handler.java:99)
04-24 19:23:15.074: E/AndroidRuntime(829):  at android.os.Looper.loop(Looper.java:137)
04-24 19:23:15.074: E/AndroidRuntime(829):  at android.app.ActivityThread.main(ActivityThread.java:4745)
04-24 19:23:15.074: E/AndroidRuntime(829):  at java.lang.reflect.Method.invokeNative(Native Method)
04-24 19:23:15.074: E/AndroidRuntime(829):  at java.lang.reflect.Method.invoke(Method.java:511)
04-24 19:23:15.074: E/AndroidRuntime(829):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
04-24 19:23:15.074: E/AndroidRuntime(829):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
04-24 19:23:15.074: E/AndroidRuntime(829):  at dalvik.system.NativeStart.main(Native Method)
04-24 19:23:15.074: E/AndroidRuntime(829): Caused by: java.lang.NullPointerException
04-24 19:23:15.074: E/AndroidRuntime(829):  at com.example.angrywordsearch.Play_Activity.onCreate(Play_Activity.java:60)
04-24 19:23:15.074: E/AndroidRuntime(829):  at android.app.Activity.performCreate(Activity.java:5008)
04-24 19:23:15.074: E/AndroidRuntime(829):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1079)
04-24 19:23:15.074: E/AndroidRuntime(829):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2023)
04-24 19:23:15.074: E/AndroidRuntime(829):  ... 11 more

所以我要问的是 如果指定要转到的类，为什么它为null？

玩活动

@Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);


        Intent Newintent = getParent().getIntent(); // Line 60
        Bundle extras = Newintent.getExtras();
        if(Newintent.hasExtra("userName"))
        {
            userName =  extras.getString("userName");
            Password = extras.getString("Password");
        }
            setContentView(R.layout.play_layout);       

    }

Answer 1

您应该使用getIntent()而不是getParent().getIntent() ， getParent()可能为null。

getIntent()提供了活动开始的意图。

Answer 2

文档说：

public final Activity getParent ()从：API级别1

如果此视图是嵌入式子级，则返回父级活动。

您的活动是嵌入式孩子吗？