In Activity.onCreate(), why does Intent.getExtras() sometimes return null?

22
votes

This was probably a false alarm, see my own answer. Original question below:

An activity has a button that takes the user to another activity. To launch the new activity, we populate our Intent with extras, and onCreate(), the new activity reads from those extras via Intent.getExtras(). We assumed the returned bundle would be non-null, but as customer crash reports discovered, getExtras() sometimes returns null.

Null-guarding the extras, as this answer shows, is perfectly fine, but if you populate the intent's extras, then why would it ever return null later? Is there a better place (like onResume()) to read the extras?

EDIT: It may be because we are not following the name convention required for the keys:

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

This is from the Intent.putExtras javadoc. What happens if you don't follow this name convention; is the behavior even defined?

Here's the relevant code:

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
    }
}

Here is a sample stack trace of this problem:

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)
4
javaandroidandroid-intentandroid-activityandroid-lifecycle
is this your complete code You are missing setContetnView . and post stacktrace. - Raghunandan
No, it's not the complete code, just the relevant stuff. - Ten-Young Guh
You haven't added any extras from what I see - codeMagic
Can you see what devices the crash reports are coming in on? I've also had a similar problem with getAction() returning null on some customer devices, where the only way to start the activity is via an action that matches an intent filter. There's definitely some weird stuff going on "out in the wild"... - Alex MDC
Maybe is not a "false alarm", I have got 9 crash reports about this NPE, and finger out that maybe there is something wrong with android 7.1, cuz all of the 9 crashes were happened on this OS version. so i bet that your crashes on the reports were also happened on this OS version, look forward for your reply, thanks. - wuzhanning

4 Answers

17
votes

You can get it like this:

getIntent().getStringExtra(key);

Or:

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

And set it like this in "FromActivity":

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

Or:

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

Either way should work, Hope this helps...

Regards!

2
votes

This was probably a false alarm; it's more likely due to our own instance variable being null:

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";

    private State state;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        state = initializeState();
        // MISSING NULL CHECK HERE!

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

        // do stuff with state and extras
    }
}
1
votes

theoretically, the Intent that starts your activity could come from anywhere, e.g. another program

0
votes

You got a null pointer error, did you miss some initialization? And can you tell us which line of your code has this error. BTW, if you have many activities to handle, set a flag for your intent is a good idea.