android - 在 onBackStackChanged() 中调用时，SDK 25.1.0 在 CommitNow 上崩溃。谷歌错误？

Question

我有一个 Activity ，包含 2 个 fragment FragmentMainOne 和 FragmentMainTwo，只要 onBackStackChanged() 被调用

public class MainActivity extends AppCompatActivity {

    private int count = 0;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
    }

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

        loadFragment();

        getSupportFragmentManager().addOnBackStackChangedListener(
                new FragmentManager.OnBackStackChangedListener() {
                    @Override
                    public void onBackStackChanged() {
                        if (getSupportFragmentManager().getBackStackEntryCount() == 0) {
                            loadFragment();
                        }
                    }
                });
    }

    public void loadSubFragment() {
        getSupportFragmentManager().beginTransaction().replace(R.id.view_container,
                new FragmentSubOne(), FragmentSubOne.TAG).addToBackStack(FragmentSubOne.TAG).commit();
    }

    public void loadFragment() {
        count++;
        if (count % 2 == 1) {
            getSupportFragmentManager().beginTransaction().replace(R.id.view_container,
                    new FragmentMainOne(), FragmentMainOne.TAG).commitNow();
        } else {
            getSupportFragmentManager().beginTransaction().replace(R.id.view_container,
                    new FragmentMainTwo(), FragmentMainTwo.TAG).commitNow();
        }
    }
}

代码在升级到 SDK 25.1.0 之前运行良好。 (即在 25.0.0 及更早版本中没问题)。

升级到 SDK 25.1.0 后，在 onBackStackChanged() 时，它会在 commitNow() 上崩溃

E/AndroidRuntime: FATAL EXCEPTION: main
              Process: com.elyeproj.commitissue, PID: 3876
              java.lang.IllegalStateException: FragmentManager is already executing transactions
                  at android.support.v4.app.FragmentManagerImpl.ensureExecReady(FragmentManager.java:1946)
                  at android.support.v4.app.FragmentManagerImpl.execSingleAction(FragmentManager.java:1965)
                  at android.support.v4.app.BackStackRecord.commitNow(BackStackRecord.java:614)
                  at com.elyeproj.commitissue.MainActivity.loadFragment(MainActivity.java:45)
                  at com.elyeproj.commitissue.MainActivity$1.onBackStackChanged(MainActivity.java:27)
                  at android.support.v4.app.FragmentManagerImpl.reportBackStackChanged(FragmentManager.java:2409)
                  at android.support.v4.app.FragmentManagerImpl.executeOpsTogether(FragmentManager.java:2157)
                  at android.support.v4.app.FragmentManagerImpl.optimizeAndExecuteOps(FragmentManager.java:2092)
                  at android.support.v4.app.FragmentManagerImpl.popBackStackImmediate(FragmentManager.java:822)
                  at android.support.v4.app.FragmentManagerImpl.popBackStackImmediate(FragmentManager.java:775)
                  at android.support.v4.app.FragmentActivity.onBackPressed(FragmentActivity.java:178)

如果我将 commitNow() 切换为 commit()，它也能正常工作。这是最新 SDK 的错误，还是我遗漏了什么？

请注意可以访问完整代码以复制问题 https://github.com/elye/issue_commitnow_sdk25_1_0(只需加载应用程序，单击“GO TO SUBFRAGMENT”，然后单击“返回”...崩溃发生。)

Answer 1

经过调查，这似乎是支持库 25.1.0 中引入的新约束。

崩溃发生在

private void ensureExecReady(boolean allowStateLoss) {
    if (mExecutingActions) {
        throw new IllegalStateException("FragmentManager is already executing transactions");
    }
    // ... more codes
}

所以某些东西已将 mExecutingActions 设置为 true。

发现在25.1.0的FragmentManager类中，下面的代码是新增的

private boolean popBackStackImmediate(String name, int id, int flags) {
    execPendingActions();
    ensureExecReady(true);

    boolean executePop = popBackStackState(mTmpRecords, mTmpIsPop, name, id, flags);
    if (executePop) {
        mExecutingActions = true;
        try {
            optimizeAndExecuteOps(mTmpRecords, mTmpIsPop);
        } finally {
            cleanupExec(); // setting mExecutingAction = false
        }
    }

    doPendingDeferredStart();
    return executePop;
}

在弹出 fragment 堆栈时将 mExecutingActions 设置为 true。 25.1.0 之前没有设置。我认为这是明确引入预防措施，以确保在提交另一个 fragment 之前完成后台堆栈弹出。

要解决此问题，只需使用 commit() if commitNow()。

有关此问题的更多说明，请参阅 https://medium.com/@elye.project/new-in-support-library-25-1-0-android-disallow-commitnow-on-onbackstackchanged-227c651eefb2#.p9ds8m8ws