更新动作条下拉正常 [英] Update actionbar dropdown properly

问题描述

在我的应用我有两个活动 - 活动A和活动B
活动A包含viewpager而活动B包含2个片段（同时添加）。这两个活动A和B有一个动作条下拉菜单，其中位置0 =去活动A和位置1 =去到活动B.

In my app I have two activities - Activity A and Activity B Activity A contains a viewpager while Activity B contains 2 fragments (added at the same time). Both Activity A and B have an actionbar dropdown menu where position 0 = go to Activity A and position 1 = go to Activity B.

在活动A的onNavigationItemSelected方法，我有：

In Activity A's onNavigationItemSelected method I have:

@Override
public boolean onNavigationItemSelected(int itemPosition, long itemId) {
    switch (itemPosition) {
    case 0:
        return true;
    case 1:
        startActivity(new Intent(this, ActivityB.class));
        return true;
    }
    return false;
}

在活动B的onNavigationItemSelected我有：

In Activity B's onNavigationItemSelected I have:

@Override
public boolean onNavigationItemSelected(int itemPosition, long itemId) {
    switch (itemPosition) {
    case 0:
        startActivity(new Intent(this, ActivityA.class));
        return true;
    case 1:
        return true;
    }

    return false;
}

在一个活动的onCreate我叫getActionBar（）setSelectedNavigationItem（0）;同样，在活动B的onCreate我叫getActionBar（）setSelectedNavigationItem（1）;

In Activity A's onCreate I call getActionBar().setSelectedNavigationItem(0); Similarly, in Activity B's onCreate I call getActionBar().setSelectedNavigationItem(1);

现在，每当我从下拉菜单中选择了一个项目，应用程序工作正常和下拉得到正确更新。然而，当我preSS回来，在下拉菜单中没有得到正确更新。事实上，它始终是相反的选择。

Now whenever I selected an item from the dropdown, the app works as expected and the dropdown gets updated correctly. However, when I press back, the dropdown menu does not get updated properly. In fact it is always on the opposite selection.

举例说，我打开应用程序，并通过动作条下拉从活动一展身手（这是第一屏）--->活动B ---->活动A ---->活动B所有。在这里，我preSS后退按钮：

For example say I open the app and go from Activity A (this is the first screen)--->Activity B---->Activity A---->Activity B all via the actionbar dropdown. From here I press the back button:

首先后退按钮preSS：我回去到活动A（但下拉选择仍然是Acitivty B）

First back button press: I go back to Activity A (but the dropdown selection remains as Acitivty B)

二后退按钮preSS：返回到活动B（下拉更新（不正确地）到活动A）

Second back button press: Go back to Activity B (dropdown updates (incorrectly) to Activity A)

第三后退按钮preSS：返回到活动A（下拉更新（不正确地）到活动B）

Third back button press: Go back to Activity A (dropdown updates (incorrectly) to Activity B)

第四后退按钮preSS：应用程序退出

Fourth back button press: App exits

我试图通过覆盖onBack pressed（）在这两个活动来解决这个问题。
在活动答：

I tried to fix this by overriding onBackPressed() in both activities. In Activity A:

@Override
public void onBackPressed() {
    actionBar.setSelectedNavigationItem(1);
}

在活动B：

    @Override
public void onBackPressed() {
    actionBar.setSelectedNavigationItem(0);
}

这实际工作（下拉选择正确获取更新）。但是，应用程序不退出（但​​我希望它以后pressing回到上backstack最终退出活动），因为backstack是没有得到弹出，因为设置里面onBack pressed的selectedNavigationItem创建一个新意图到其他活动

This actually works (the dropdown selection gets updated correctly). However, the app never exits (but I want it to exit after pressing back on the final activity on the backstack), as the backstack isn't getting popped because setting the selectedNavigationItem inside onBackPressed creates a new intent to the other activity.

如何才能让这个pressing后退按钮弹出backstack（而不是创建一个新的intent），而正确更新导航下拉？我是什么，从这个看似简单的问题不见了？

How can make it so that pressing the back button pops the backstack (instead of creating a new intent) while correctly updating the navigation dropdown? What am I missing from this seemingly simple problem?

在此先感谢！

推荐答案

尝试使用invalidateOptionsMenu（）方法

Try using invalidateOptionsMenu() method

@Override
public void onBackPressed() {
    getActivity().invalidateOptionsMenu();
}

invalidateOptionsMenu（）的说明：
的http://developer.android.com/reference/android/app/Activity.html#invalidateOptionsMenu()

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