java - 在Activity.onCreate()中，为什么Intent.getExtras()有时会返回null？

Question

这可能是个误报，见 my own answer .以下原始问题:

一个 Activity 有一个将用户带到另一个 Activity 的按钮。为了启动新的 Activity ，我们用额外的内容填充我们的 Intent，然后 onCreate()，新的 Activity 通过 Intent.getExtras() 从这些额外的内容中读取。我们假设返回的 bundle 不为 null，但随着客户崩溃报告的发现，getExtras() 有时会返回 null。

null 保护额外的，如 this answer shows , 完全没问题，但是如果您填充了 Intent 的附加内容，那么为什么它以后会返回 null 呢？有没有更好的地方(比如 onResume())来阅读额外内容？

编辑:这可能是因为我们没有遵循键所需的名称约定:

The name must include a package prefix, for example the app com.android.contacts would use names like "com.android.contacts.ShowAll".

这是来自 Intent.putExtras javadoc .如果您不遵循此名称约定会发生什么；行为是否已定义？

以下是相关代码:

class FromActivity extends Activity {

    ImageButton button;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.from_view);

        button = (ImageButton)findViewById(R.id.button);
        button.setVisibility(View.VISIBLE);
        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent i = new Intent(FromActivity.this, ToActivity.class);
                i.putExtra(ToActivity.SERVER_PARAM, ...);
                i.putExtra(ToActivity.UUID_PARAM, ...);
                i.putExtra(ToActivity.TEMPLATE_PARAM, ...);
                startActivityForResult(i, 0); 
                overrideTransition(R.anim.slide_left_in, R.anim.slide_left_out);
            }
        });
    }

}

class ToActivity extends Activity {

    public static final String SERVER_PARAM = "server";
    public static final String UUID_PARAM = "uuid";
    public static final String TEMPLATE_PARAM = "template";

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

        Bundle extras = getIntent().getExtras();
        if (extras == null) {
            finish();
            return;
        }

        // do stuff with extras
    }
}

这是此问题的示例堆栈跟踪:

java.lang.RuntimeException: Unable to start activity ComponentInfo{ToActivity}: java.lang.NullPointerException
    at  android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2355)
    at  android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2391)
    at  android.app.ActivityThread.access$600(ActivityThread.java:151)
    at  android.app.ActivityThread$H.handleMessage(ActivityThread.java:1335)
    at  android.os.Handler.dispatchMessage(Handler.java:99)
    at  android.os.Looper.loop(Looper.java:155)
    at  android.app.ActivityThread.main(ActivityThread.java:5493)
    at  java.lang.reflect.Method.invokeNative(Native Method)
    at  java.lang.reflect.Method.invoke(Method.java:511)
    at  com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1028)
    at  com.android.internal.os.ZygoteInit.main(ZygoteInit.java:795)
    at  dalvik.system.NativeStart.main(Native Method)
     Caused by: java.lang.NullPointerException
    at  ToActivity.onCreate(SourceFile:49)
    at  android.app.Activity.performCreate(Activity.java:5066)
    at  android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1101)
    at  android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2311)
     ... 11 more
     java.lang.NullPointerException
    at  ToActivity.onCreate(SourceFile:49)
    at  android.app.Activity.performCreate(Activity.java:5066)
    at  android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1101)
    at  android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2311)
    at  android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2391)
    at  android.app.ActivityThread.access$600(ActivityThread.java:151)
    at  android.app.ActivityThread$H.handleMessage(ActivityThread.java:1335)
    at  android.os.Handler.dispatchMessage(Handler.java:99)
    at  android.os.Looper.loop(Looper.java:155)
    at  android.app.ActivityThread.main(ActivityThread.java:5493)
    at  java.lang.reflect.Method.invokeNative(Native Method)
    at  java.lang.reflect.Method.invoke(Method.java:511)
    at  com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1028)
    at  com.android.internal.os.ZygoteInit.main(ZygoteInit.java:795)
    at  dalvik.system.NativeStart.main(Native Method)

Answer 1

你可以这样得到:

getIntent().getStringExtra(key);

或者:

getIntent().getExtras().getString(key)

并在“FromActivity”中这样设置:

Bundle extras = new Bundle();
extras.putString(key, value);
intent.putExtras(extras);
//And start your activity...

或者:

intent.putExtra(key, string);
//And start your activity...

无论哪种方式都应该有效，希望这会有所帮助......

问候!