android - 按下硬件后退按钮时如何返回到上一个 fragment

Question

我是 android 开发的初学者，我想配置硬件后退按钮返回到上一个 fragment ， fragment 标题也应该根据当前 fragment 改变， 这是我的主要 Activity 来源:

import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentTransaction;
import android.support.v4.widget.DrawerLayout;
import android.support.v7.app.ActionBarActivity;
import android.support.v7.widget.Toolbar;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Toast;


public class MainActivity extends ActionBarActivity implements FragmentDrawer.FragmentDrawerListener {

    private static String TAG = MainActivity.class.getSimpleName();

    private Toolbar mToolbar;
    private FragmentDrawer drawerFragment;

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

        mToolbar = (Toolbar) findViewById(R.id.toolbar);

        setSupportActionBar(mToolbar);
        getSupportActionBar().setDisplayShowHomeEnabled(true);

        drawerFragment = (FragmentDrawer)
                getSupportFragmentManager().findFragmentById(R.id.fragment_navigation_drawer);
        drawerFragment.setUp(R.id.fragment_navigation_drawer, (DrawerLayout) findViewById(R.id.drawer_layout), mToolbar);
        drawerFragment.setDrawerListener(this);

        // display the first navigation drawer view on app launch
        displayView(0);
    }


    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.menu_main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }

        if(id == R.id.action_search){
           Toast.makeText(getApplicationContext(), "Search action is selected!", Toast.LENGTH_SHORT).show();
            return true;
     }

    return super.onOptionsItemSelected(item);
    }

    @Override
    public void onDrawerItemSelected(View view, int position) {
        displayView(position);
    }

    private void displayView(int position) {
        Fragment fragment = null;
        String title = getString(R.string.app_name);
        switch (position) {
            case 0:
                fragment = new HomeFragment();
                title = getString(R.string.title_home);
                break;
            case 1:
                fragment = new MicrosoftDskFragment();
                title = "Microsoft Dsk";
                break;
            case 2:
                fragment = new GoogleDskFragment();
                title = "Google Dsk";
                break;
            case 3:
                fragment = new AppleDskFragment();
                title = "Apple Dsk";
                break;
            case 4:
                fragment = new OthersDskFragment();
                title = "Others Dsk";
                break;
            case 5:
                fragment = new AboutUSFragment();
                title = "About US";
                break;
            default:
                break;
        }


        if (fragment != null) {
            FragmentManager fragmentManager = getSupportFragmentManager();
            FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
            fragmentTransaction.replace(R.id.container_body, fragment);
            fragmentTransaction.addToBackStack(null).commit();

            // set the toolbar title
            getSupportActionBar().setTitle(title);
        }
    }
} 

请帮我解决这个问题。

Answer 1

您正在将事务添加到后台堆栈，因此为了返回到前一个事务，您需要做的就是:

FragmentManager fragmentManager = getSupportFragmentManager();
fragmentManager.popBackstack(null, 0);

你也可以考虑给每个fragment加一个id，调用的时候传过去

fragmentTransaction.addToBackStack(null).commit();

而不是空值。这样，您将能够执行此操作:

fragmentTransaction.addToBackStack(myFragmentId).commit();

//Later on...

FragmentManager fragmentManager = getSupportFragmentManager();
fragmentManager.popBackstack(myFragmentId, 0);

返回到特定 fragment ，而不仅仅是最后一个 fragment :-)