addToBackStack 不工作

Question

我正在尝试关闭片段并希望通过在片段实现中使用 addToBackStack 来恢复主要活动，但它不起作用。后退按钮正在关闭应用程序。

我使用的片段实现方法是，

  private void dispaySelectedScreen(int id) {
    Fragment fragment = null;

    switch (id) {
        case R.id.facebook_login:
            fragment = new FacebookLogin();
            break;
        case R.id.memes:
            fragment = new Memes();
            break;
        case R.id.submit_image:
            fragment = new SubmitImage();
            break;
        case R.id.discussion:
            fragment = new Discussions();
            break;
        case R.id.invite:
            fragment = new Invite();
            break;
        case R.id.connect_fb:
            fragment = new FacebookConnect();
            break;
        case R.id.connect_twitter:
            fragment = new TwitterConnect();
            break;
        case R.id.connect_instagram:
            fragment = new InstaConnect();
            break;
    }

    if (fragment != null) {
        FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
        ft.replace(R.id.content_main, fragment);
        ft.addToBackStack(null);
        ft.commit();




    }

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

我还为抽屉声明了一个 onBackPressed 方法，

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


    }

请建议..

Answer 1

fragment.addToBackStack(null) 足以打开上一个活动，但是如果您想在除删除片段之外处理后按操作，那么我们将覆盖 onBackPressed()，所以这是我的经过测试的方法，请看一下：-

下面是我的实现：-

@Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        getSupportFragmentManager().beginTransaction().replace(R.id.fragment_holder, new MyFragment(), "MY_FRAG")
                .addToBackStack(null).commit();
    }

    @Override
    public void onBackPressed() {
        MyFragment fragment = (MyFragment) getSupportFragmentManager().findFragmentByTag("MY_FRAG");
        if (fragment != null) {
            if (fragment.isVisible()) {
                //todo perform any action if you want when fragment is removed
            }
        } else {
            super.onBackPressed();
        }
    }

Answer 2

我看到你在事务上使用替换，这样你的片段将从堆栈中弹出，但它会重新加载，即该片段的 onCreateView() 将被调用。只需替换

 ft.replace(R.id.content_main, fragment);

到

 ft.add(R.id.content_main, fragment);

要处理后退按钮，请使用以下代码。

public void onBackPressed() {
if (drawer.isDrawerOpen(GravityCompat.START)) {
    drawer.closeDrawer(GravityCompat.START);
} else {
    if (getSupportFragmentManager().getBackStackEntryCount() == 0) {
        //that means your stack is empty and you want to close activity
        finish();
    } else {
        // pop the backstack here
        getSupportFragmentManager().popBackStackImmediate();
    }
}

}