Android：如果应用在后台运行，如何弹出 Fragment 的 BackStack？

Question

我有一个碎片监控一些应用程序的添加/删除状态，当这种情况发生时，我需要替换为另一个碎片，并从返回堆栈中删除第一个碎片（因为我不想再回到它）。

但是，当应用程序在后台运行时，popBackStack总是会抛出异常：

06-06 14:44:39.264: E/AndroidRuntime(9428): Process: com.mmx.smarthome, PID: 9428
06-06 14:44:39.264: E/AndroidRuntime(9428): java.lang.IllegalStateException: Can not perform this action after onSaveInstanceState
06-06 14:44:39.264: E/AndroidRuntime(9428):     at android.support.v4.app.FragmentManagerImpl.checkStateLoss(FragmentManager.java:1354)
06-06 14:44:39.264: E/AndroidRuntime(9428):     at android.support.v4.app.FragmentManagerImpl.enqueueAction(FragmentManager.java:1372)
06-06 14:44:39.264: E/AndroidRuntime(9428):     at android.support.v4.app.FragmentManagerImpl.popBackStack(FragmentManager.java:499)
06-06 14:44:39.264: E/AndroidRuntime(9428):     at com.mmx.aircon.band.BandSportsFragment.gotoBandControlFragment(BandSportsFragment.java:160)
06-06 14:44:39.264: E/AndroidRuntime(9428):     at com.mmx.aircon.band.BandSportsFragment.handleMessage(BandSportsFragment.java:220)
06-06 14:44:39.264: E/AndroidRuntime(9428):     at com.mmx.aircon.common.NoLeakHandler$WeakRefHandler.handleMessage(NoLeakHandler.java:137)
06-06 14:44:39.264: E/AndroidRuntime(9428):     at android.os.Handler.dispatchMessage(Handler.java:102)
06-06 14:44:39.264: E/AndroidRuntime(9428):     at android.os.Looper.loop(Looper.java:136)
06-06 14:44:39.264: E/AndroidRuntime(9428):     at android.app.ActivityThread.main(ActivityThread.java:5047)
06-06 14:44:39.264: E/AndroidRuntime(9428):     at java.lang.reflect.Method.invokeNative(Native Method)
06-06 14:44:39.264: E/AndroidRuntime(9428):     at java.lang.reflect.Method.invoke(Method.java:515)
06-06 14:44:39.264: E/AndroidRuntime(9428):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
06-06 14:44:39.264: E/AndroidRuntime(9428):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:609)
06-06 14:44:39.264: E/AndroidRuntime(9428):     at dalvik.system.NativeStart.main(Native Method)

以下是代码：

private void gotoBandControlFragment() {
    Fragment bandControlFragment = new BandControlFragment(getActivity());
    FragmentManager fragmentManager = getFragmentManager();
    fragmentManager.popBackStack(null,
            FragmentManager.POP_BACK_STACK_INCLUSIVE);
    FragmentTransaction ft = fragmentManager.beginTransaction();

    ft.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_OPEN);
    ft.replace(R.id.view_fragment, bandControlFragment, null);
    ft.commitAllowingStateLoss();
}

我尝试重写 onSaveInstanceState 方法，但并没有起到帮助作用。

@Override
public void onSaveInstanceState(Bundle outState) {
}

如何对其进行弹出操作？

- mianlaoshu

---

你解决了吗？ - carlosavoy

有人有解决方案吗？ - Hiren Patel

Answer 1

如果应用程序在后台运行，您可以提高一个布尔标志来记住当应用程序回到前台时应调用该方法。使用Android活动生命周期回调：

private boolean mIsVisible = false;

@Override
protected void onResume() {
    super.onResume();

    mIsVisible = true;

    if (mShouldGoToBandControlFragment) {
        gotoBandControlFragment();
    }
}

@Override
protected void onPause() {
    mIsVisible = false;
    super.onPause();
}

private void gotoBandControlFragment() {
    if (mIsVisible) {
        mShouldGoToBandControlFragment = false;
        Fragment bandControlFragment = new BandControlFragment(getActivity());
        FragmentManager fragmentManager = getFragmentManager();
        fragmentManager.popBackStack(null,
                FragmentManager.POP_BACK_STACK_INCLUSIVE);
        FragmentTransaction ft = fragmentManager.beginTransaction();

        ft.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_OPEN);
        ft.replace(R.id.view_fragment, bandControlFragment, null);
        ft.commitAllowingStateLoss();
    } else {
        mShouldGoToBandControlFragment = true;
    }
}

- Alex Kuzmin