Question

我有一个带有Framelayout和BottomNavigationView的活动......我有4个片段（A，B，C，D）......当我点击要加载的菜单项后从A切换到B时片段B，片段A被破坏...我在片段生命周期中涉及的所有回调方法（OnAttach，OnCreate，OnCreateView .....等）上添加了一条Log消息，当我更改片段时，onDestroyView总是被调用...所以当我回到之前打开的片段时，再次调用onCreateView ..

这是我的活动课程：

    public class Home extends AppCompatActivity
{
    private BottomNavigationView.OnNavigationItemSelectedListener 
mOnNavigationItemSelectedListener
        = new BottomNavigationView.OnNavigationItemSelectedListener() {

    @Override
    public boolean onNavigationItemSelected(@NonNull MenuItem item)
    {
        Fragment fragment = null;
        Fragment currentFragment = getSupportFragmentManager().findFragmentById(R.id.fragment_container);
        switch (item.getItemId())
        {
            case R.id.navigation_a:
                if (!(currentFragment instanceof FragmentA))
                    fragment = FragmentA.newInstance();
                break;
            case R.id.navigation_b:
                if (!(currentFragment instanceof FragmentB))
                    fragment = FragmentB.newInstance();
                break;
            case R.id.navigation_c:
                if (!(currentFragment instanceof FragmentC))
                    fragment = FragmentC.newInstance();
                break;
            case R.id.navigation_d:
                if (!(currentFragment instanceof FragmentD))
                    fragment = FragmentD.newInstance();
                break;
        }

        if (fragment != null) {
            getSupportFragmentManager().beginTransaction().replace(R.id.fragment_container, fragment).commit();
            return true;
        }

        return false;
    }

};


//TODO Handle life-cycle methods when switching between fragments
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_home);
    Toolbar toolbar = findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);

    FragmentManager fm = getSupportFragmentManager();
    fm.beginTransaction()
            .add(R.id.fragment_container, FragementA.newInstance())
            .commit();
    fm.popBackStack();

    BottomNavigationView navigation = findViewById(R.id.navigation);        navigation.setOnNavigationItemSelectedListener(mOnNavigationItemSelectedListener);
}

public boolean onKeyDown(int keyCode, KeyEvent event)
{
    if (keyCode == KeyEvent.KEYCODE_BACK)
    {
        moveTaskToBack(true);
        return true;
        }

    return false;
    }

}

我想知道实际上我在这里失踪了什么......提前致谢

Answer 1

好吧，你没有将片段添加到后台堆栈。

Answer 2

您每次点击都会创建新实例。

如果你想用同一个替换那些，请保留对那些的引用或者然后添加到fragmentransaction的backstack，但是你需要使用标签来导航以前的那些。

Answer 3

尝试将setRetainInstance(true);用于您的片段。

// this method is only called once for this fragment
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    // retain this fragment
    setRetainInstance(true);
}

在bottomnavigationview更改项目点击

3 个答案: