java.lang.RuntimeException : Unable to resume activity with java. lang.IllegalArgumentException

Question

最近我有时在 MainActivity 调用 onResume() 时遇到这个异常。

java.lang.RuntimeException: Unable to resume activity {com.qau4d.c35s3.androidapp/com.xxx.XXX.XXX.MainActivity}: java.lang.IllegalArgumentException
at android.app.ActivityThread.performResumeActivity(ActivityThread.java:3400)
at android.app.ActivityThread.handleResumeActivity(ActivityThread.java:3440)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1510)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6077)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:865)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:755)
Caused by: java.lang.IllegalArgumentException
at android.os.Parcel.readException(Parcel.java:1687)
at android.os.Parcel.readException(Parcel.java:1636)
at android.app.ActivityManagerProxy.isTopOfTask(ActivityManagerNative.java:5475)
at android.app.Activity.isTopOfTask(Activity.java:5961)
at android.app.Activity.onResume(Activity.java:1252)
at com.qau4d.c35s3.androidapp.onResume(XActivity.java:29)
at com.qau4d.c35s3.androidapp.onResume(MainActivity.java:196)
at android.app.Instrumentation.callActivityOnResume(Instrumentation.java:1269)
at android.app.Activity.performResume(Activity.java:6768)
at android.app.ActivityThread.performResumeActivity(ActivityThread.java:3377)

在MainActivity和父类(super class)XActivity中，只调用了super.onResume();。正常开发了很久才出现这个异常，真的很奇怪，查了一些相关的引用资料都没有。

Answer 1

在Activity#isTopOfTask方法中我们可以看到:

private boolean isTopOfTask() {
    if (mToken == null || mWindow == null) {
        return false;
    }
    try {
        return ActivityManager.getService().isTopOfTask(getActivityToken());
    } catch (RemoteException e) {
        return false;
    }
}

在 ActivityManagerService#isTopOfTask 我们可以找到:

@Override
public boolean isTopOfTask(IBinder token) {
    synchronized (this) {
        ActivityRecord r = ActivityRecord.isInStackLocked(token);
        if (r == null) {
            throw new IllegalArgumentException();
        }
        return r.task.getTopActivity() == r;
    }
}

所以，我认为 ActivityRecord 为 null。但我不知道为什么它为 null....