Question

我有一个在NavigationDrawer中有多个片段的应用程序。

以下是我的代码：

@Override
    public boolean onPrepareOptionsMenu(Menu menu) {
        // if nav drawer is opened, hide the action items
        boolean drawerOpen = mDrawerLayout.isDrawerOpen(mDrawerList);
        menu.findItem(R.id.action_search).setVisible(!drawerOpen);
        return super.onPrepareOptionsMenu(menu);
    }

    /**
     * Diplaying fragment view for selected nav drawer list item
     * */
    private void displayView(int position) {
        // update the main content by replacing fragments
        fragment = null;

        switch (position) {
        case 0:
            fragment = new HomeFragment();
            break;
        case 1:
            fragment = new GalleryFragment();
            break;
        case 2:
            fragment = new ContactFragment();
            break;
        default:
            break;
        }

        if (fragment != null) {
            FragmentManager fragmentManager = getFragmentManager();
            fragmentManager.beginTransaction()
                    .replace(R.id.frame_container, fragment).commit();

            // update selected item and title, then close the drawer
            mDrawerList.setItemChecked(position, true);
            mDrawerList.setSelection(position);
            setTitle(navMenuTitles[position]);
            mDrawerLayout.closeDrawer(mDrawerList);
        } else {
            // error in creating fragment
            Log.e("MainActivity", "Error in creating fragment");
        }
    }

    @Override
    public void setTitle(CharSequence title) {
        mTitle = title;
        getActionBar().setTitle(mTitle);
    }

    /**
     * When using the ActionBarDrawerToggle, you must call it during
     * onPostCreate() and onConfigurationChanged()...
     */

    @Override
    protected void onPostCreate(Bundle savedInstanceState) {
        super.onPostCreate(savedInstanceState);
        // Sync the toggle state after onRestoreInstanceState has occurred.
        mDrawerToggle.syncState();
    }

    @Override
    public void onConfigurationChanged(Configuration newConfig) {
        super.onConfigurationChanged(newConfig);
        // Pass any configuration change to the drawer toggls
        mDrawerToggle.onConfigurationChanged(newConfig);

    }


    @Override
    public void onBackPressed() {

        if (fragment != null) {
            FragmentManager fragmentManager = getFragmentManager();
            fragmentManager.beginTransaction()
                    .add(R.id.frame_container, fragment).commit();

            int position = 0;
            fragment = new HomeFragment();

            // update selected item and title, then close the drawer
            mDrawerList.setItemChecked(position, true);
            mDrawerList.setSelection(position);
            setTitle(navMenuTitles[position]);
            mDrawerLayout.closeDrawer(mDrawerList);
        } else {
            // error in creating fragment
            Log.e("MainActivity", "Error in creating fragment");
        } 



    }

它基本上是什么，首先是HomeFragment，当我想去另一个fragment MediaFragment并决定回去按后退按钮时，我想去HomeFragment，当我想要关闭应用程序时再次按下后退按钮，它现在将像gmail应用程序一样关闭应用程序。我怎样才能做到这一点？我使用我放在onBackPressed()中的代码时遇到了问题。每当我转到其他片段时，HomeFragment就会显示出来。有任何想法吗？非常感谢您的帮助。

更新：在我MediaFragment之前按下后退按钮之前，它会自动关闭应用。它不应该是，但它应该转到HomeFragment，当它在HomeFragment时，我点击后退按钮然后它将关闭应用程序。

Answer 1

为什么不跟踪选择的最后位置，而不是在onBackPressed中复制你的代码？

int selectedPosition = 0;

private void displayView(int position) {
    ... // All your current code
    selectedPosition = position;
}

@Override
public void onBackPressed() {
    if (selectedPosition != 0) {
        displayView(0);
    } else {
        super.onBackPressed();
}

Answer 2

为什么不在执行交易时简单地将片段添加到backstack，如@Raghunandan所说。见下面的代码，

 if (fragment != null) {
        FragmentTransaction fragmentTransaction = getFragmentManager().beginTransaction()
                .replace(R.id.frame_container, fragment).commit(); //Changed from fragmentManager to FragmentTrasaction 

        fragmentTransaction.addToBackStack(null); //this will add the fragment to backstack and hence pressing back will take to previous trasaction

        // update selected item and title, then close the drawer
        mDrawerList.setItemChecked(position, true);
        mDrawerList.setSelection(position);
        setTitle(navMenuTitles[position]);
        mDrawerLayout.closeDrawer(mDrawerList);
    } else {
        // error in creating fragment
        Log.e("MainActivity", "Error in creating fragment");
    }

当您退出时，不要添加HomeFragment else，在您退出应用程序之前会看到一个空白页面（或类似的东西）（您必须再次按回来，以避免添加HomeFragment）。将除此之外的所有片段添加到Backstack中，您将能够按照自己的意愿继续操作。此外，当您从片段加载活动时，它会自动由应用程序在Backstack中维护，因此无需担心。

请根据您的要求告诉我。

Android返回导航抽屉中的第一个片段

2 个答案: