Question

阅读this并在Android文档中搜索后，我放弃了，并决定在这里询问。我尝试在Navigation Drawer中设置后退按钮，以便应用仅从Home片段关闭，其他任何片段都会将我们带回Home。例如，如果我们从Home片段开始并导航到导航抽屉中的其他片段，当我们点击后退按钮时，我们将转到Home片段，如果我们从Home片段回击，我们将退出该应用。

我试图像这样实现它：

public void onNavigationDrawerItemSelected(int position) {   
    ...
    // If the next fragment is Home, clear the backstack.
    if (frag instanceof Home) {
        getSupportFragmentManager().popBackStack();
        fragmentManager.beginTransaction().replace(R.id.container, frag)
                .commit();
    }
    // If the backstack already contains a transaction, replace the current fragment
    else if (getSupportFragmentManager().getBackStackEntryCount() > 0) {
        fragmentManager.beginTransaction().replace(R.id.container, frag)
                .commit();
    } 
    // If the backstack is empty, insert the Home -> Fragment transaction
    else {
        fragmentManager.beginTransaction().replace(R.id.container, frag)
                .addToBackStack("").commit();
    }
    ...
}

    ...

@Override
public void onBackPressed() {

    if (drawerLayout.isDrawerOpen(Gravity.START)) {
        drawerLayout.closeDrawer(Gravity.LEFT);
    } else {
        super.onBackPressed();
        // If returning back to Home fragment, restore action bar title.
        if (getSupportFragmentManager().getBackStackEntryCount() > 0)
            onSectionAttached(0);
    }
}

我附加的链接无法正常工作，我实施的方式并不一致。例如，如果我从Home导航到其他片段并返回主页（不按后退按钮），我的片段会相互叠加。

Answer 1

我刚刚找到了一种让这项工作变得相当简单的方法，所以我决定将它发布在这里：

// Are we in Home fragment?
private boolean homeFrag = true;
...
@Override
public void onNavigationDrawerItemSelected(int position) {
    ...
    // Next fragment is Home?
    if (frag instanceof Home)
        homeFrag = true;
    else
        homeFrag = false;

    fragmentManager.beginTransaction().replace(R.id.container, frag)
            .commit();
    onSectionAttached(position);
}
...
@Override
public void onBackPressed() {
    // Close navigation drawer if open
    if (drawerLayout.isDrawerOpen(Gravity.START)) {
        drawerLayout.closeDrawer(Gravity.LEFT);
    } else {
        // If not in Home, move back to Home.
        if (!homeFrag) {
            onNavigationDrawerItemSelected(0);
        } else
            super.onBackPressed();
    }
}

我想听听您对此解决方案的看法。

Answer 2

我认为你在onBackPressed方法中对nav ul ul { height: auto; display: none; position:absolute; background-color: #399077; margin-left: 89.5%; //top: 9%; delete this line margin-top: -38px; //add this line z-index:150; }的调用应该是else块中的最后一个代码。原因是方法调用可能会影响getBackStackEntryCount（）中的计数。我认为这些电话已经太多了。

Answer 3

我已经制作了这种方法，可以为你管理片段和后台堆栈。

/**
 * Change the current displayed fragment managing fragment backstack
 * 
 * @param frag the fragment to display
 * @param saveInBackstack true if you want the previous to be in backstack
 */
private void changeFragment(Fragment frag, boolean saveInBackstack) {
    String backStateName = ((Object) frag).getClass().getName();

    try {
        FragmentManager manager = getSupportFragmentManager();
        boolean fragmentPopped = manager.popBackStackImmediate(backStateName, 0);

        if (!fragmentPopped && manager.findFragmentByTag(backStateName) == null) { //fragment not in back stack, create it.
            FragmentTransaction transaction = manager.beginTransaction();
            transaction.replace(R.id.main_fragment_container, frag, ((Object) frag).getClass().getName());

            if (saveInBackstack) {
                Log.d(TAG, "Change Fragment : addToBackTack");
                transaction.addToBackStack(backStateName);
            } else {
                Log.d(TAG, "Change Fragment : NO addToBackTack");
            }

            transaction.commit();
        } else {
            Log.d(TAG, "Change Fragment : nothing to do");
            // custom effect if fragment is already instanciated
        }
    } catch (IllegalStateException exception) {
        Log.e(TAG, "Unable to commit fragment, could be activity as been killed in background. " + exception.toString());
    }
}

同样在您的活动中，覆盖onBackPressed：

@Override
public void onBackPressed() {
    int fragments = getFragmentManager().getBackStackEntryCount();
    if (fragments == 1) {
        finish();
    }
    super.onBackPressed();
}

导航抽屉后退按钮到主片段

3 个答案: