Question

所以我只有一个活动是MainActivity。所有其他部分都是碎片形式。

所以，如果我们去公告，基本上，会发生什么

MainActivity -> AnnouncementsFragment-> AnnouncementDetailFragment

我想要发生的是当用户按两次后退键时，他返回上一个片段而不是关闭它。

MainActivity <- AnnouncementsFragment <- AnnouncementDetailFragment

根据研究，我发现这段代码很遗憾不适用于我的实例。顺便说一下，我正在使用导航边栏。

@Override
public void onBackPressed() {
    DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
    if (drawer.isDrawerOpen(GravityCompat.START)) {
        drawer.closeDrawer(GravityCompat.START);
    } else if(getFragmentManager().getBackStackEntryCount() > 0) {
        getFragmentManager().popBackStack();
    } else {
        super.onBackPressed();
    }

}

布局/ content_main

基本上，我在content_main.xml中所做的只是可替换数据的容器。

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/content_main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    app:layout_behavior="@string/appbar_scrolling_view_behavior"
    tools:context="com.techdepot_ph.maco.iannounce.MainActivity"
    tools:showIn="@layout/app_bar_main">

    <ImageView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        app:srcCompat="@drawable/sti_overlay_bg"
        android:layout_marginTop="84dp"
        android:id="@+id/imageView4"
        android:layout_alignParentTop="true"
        android:layout_centerHorizontal="true" />

    <FrameLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_alignParentTop="true"
        android:layout_alignParentLeft="true"
        android:layout_alignParentStart="true"
        android:id="@+id/root_layout">

    </FrameLayout>
</RelativeLayout>

启动片段

我在启动片段时所做的是用户点击导航栏中的项目

@SuppressWarnings("StatementWithEmptyBody")
@Override
public boolean onNavigationItemSelected(MenuItem item) {
    // Handle navigation view item clicks here.
    int id = item.getItemId();

    if (id == R.id.nav_message) {

        getSupportActionBar().setTitle("Create Announcement");

        fragment = new CreateMessageFragment();
        FragmentManager fm = getFragmentManager();
        FragmentTransaction ft = fm.beginTransaction();
        ft.replace(R.id.root_layout, fragment);
        ft.commit();

    } else if (id == R.id.nav_announcements) {

        getSupportActionBar().setTitle("Announcements");

        fragment = new AnnouncementsFragment();
        FragmentManager fm = getFragmentManager();
        FragmentTransaction ft = fm.beginTransaction();
        ft.replace(R.id.root_layout, fragment);
        ft.commit();

    } 

    DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
    drawer.closeDrawer(GravityCompat.START);
    return true;
}

Answer 1

在提交新片段之前，请将之前的片段添加到backstack。

getSupportFragmentManager().beginTransaction()
                       .add(detailFragment, "detail")
                       // Add this transaction to the back stack
                       .addToBackStack()
                       .commit();

在这里阅读更多内容。

https://developer.android.com/reference/android/app/FragmentTransaction.html#addToBackStack(java.lang.String)

Answer 2

加载片段时将它们添加到backstack

fragment = new CreateMessageFragment();
    FragmentManager fm = getFragmentManager();
    FragmentTransaction ft = fm.beginTransaction();
    ft.replace(R.id.root_layout, fragment);
    ft.addToBackStack(null)
    ft.commit();

并在您的活动中按

 private Boolean exit = false;
  @Override
     public void onBackPressed() {
if (exit) {

      if (getSupportFragmentManager().getBackStackEntryCount() > 0 ){
       getSupportFragmentManager().popBackStack();
          }
 else
          super.onbackpress();       
              } 

       else {

                  exit = true;
                  new Handler().postDelayed(new Runnable() {
                      @Override
                      public void run() {
                          exit = false;
                      }
                  }, 3 * 1000);
              }

回到之前的片段

2 个答案: