如何在按下后退按钮时退出 Android 导航抽屉

Question

我发现之前问过类似的问题并尝试了一些；但不适合我。

我有一个主要活动，布局中有一个片段容器。我有 3 个片段将根据抽屉式导航选择替换为片段容器。我正在将所有交易添加到后台堆栈。

我想将带有 Tracker 片段的活动设置为主屏幕，这样当用户按下返回按钮时，他应该转到第一个片段。如果他已经在第一个片段中，则应用程序应该退出。

这是我的代码：

@Override
public void onNavigationDrawerItemSelected(int position) {
    // update the main content by replacing fragments
    fragmentManager = getFragmentManager();
    Fragment fragment;
    switch (position){
        case 0:
            fragment = TrackerFragment.newInstance(position);
            break;

        case 1:
            fragment = CalendarViewFragment.newInstance(position);
            break;
        case 2:
            fragment = SettingsFragment.newInstance(position);

            break;
        default:
            fragment = TrackerFragment.newInstance(position);
    }

    fragmentManager.beginTransaction()
            .replace(R.id.container, fragment).addToBackStack(null)
            .commit();

}

我不确定如何在 OnBackPressed 方法上处理这种情况。我应该做什么逻辑。有没有什么方法可以在不添加回栈的情况下做到这一点？ 非常感谢任何帮助！ 谢谢1

Answer 1

private int mCurrentFragmentPosition;
 @Override
public void onNavigationDrawerItemSelected(int position) {

    // update the main content by replacing fragments

    mCurrentFragmentPosition = position;
    fragmentManager = getFragmentManager();
    Fragment fragment;
    switch (position){
        case 0:
            fragment = TrackerFragment.newInstance(position);
            break;

        case 1:
            fragment = CalendarViewFragment.newInstance(position);
            break;
        case 2:
            fragment = SettingsFragment.newInstance(position);

            break;
        default:
            fragment = TrackerFragment.newInstance(position);
    }

    fragmentManager.beginTransaction()
            .replace(R.id.container, fragment)
            .commit();

}
@Override
public void onBackPressed() {
    if(mCurrentFragmentPosition != 0){
        onNavigationDrawerItemSelected(0);
    }
    else {
        finish();
    }
}

Answer 2

只需跟踪当前显示的片段并覆盖onBackPressed 相应的行为。不需要用 backstack 让你的生活复杂化:)

int currentFragmentPosition = 0;

@Override
public void onNavigationDrawerItemSelected(int position) {
    // update the main content by replacing fragments
    if(postion == currentFragmentPosition)
    {
       return;
    }
    currentFragmentPosition = position;
    fragmentManager = getFragmentManager();
    Fragment fragment;
    switch (position){
        case 0:
            fragment = TrackerFragment.newInstance(position);
            break;

        case 1:
            fragment = CalendarViewFragment.newInstance(position);
            break;
        case 2:
            fragment = SettingsFragment.newInstance(position);

            break;
        default:
            fragment = TrackerFragment.newInstance(position);
    }

    fragmentManager.beginTransaction()
            .replace(R.id.container, fragment).addToBackStack(null)
            .commit();
}

@Override
public void onBackPressed() {
   if(currentFragmentPostion != 0){
      onNavigationDrawerItemSelected(0);
    }
    else {
      finish();
    }
}