防止抽屉式导航片段

Question

最近我的工作我的应用程序，使其加载速度更快，工作得更好，我使用的导航抽屉里我的MainActivity：

@Override 
public boolean onNavigationItemSelected(MenuItem item) { 

    // Handle navigation view item clicks here. 
    int id = item.getItemId(); 

    if (id == R.id.nav_camara) { 
     LoadJson asyncTask = (LoadJson) new LoadJson(new LoadJson.AsyncResponse() { 
      @Override 
      public void processFinish(JSONArray output) { 
       //Here you will receive the result fired from async class 
       //of onPostExecute(result) method. 
       //Set the fragment initially 
       MainFragment fragment = new MainFragment(output); 
       FragmentTransaction fragmentTransaction = 
         getSupportFragmentManager().beginTransaction(); 
       fragmentTransaction.add(R.id.fragment_container, fragment); 
       fragmentTransaction.commit(); 
       // Handle the camera action 
      } 
     }).execute(); 


    } else if (id == R.id.nav_gallery) { 
     //Set the fragment initially 
     GalleryFragment fragment = new GalleryFragment(); 
     FragmentTransaction fragmentTransaction = 
       getSupportFragmentManager().beginTransaction(); 
     fragmentTransaction.replace(R.id.fragment_container, fragment); 
     fragmentTransaction.commit(); 


    } else if (id == R.id.nav_search) { 
     //Set the fragment initially 
     FetchResualt fragment = new FetchResualt(); 
     FragmentTransaction fragmentTransaction = 
       getSupportFragmentManager().beginTransaction(); 
     fragmentTransaction.replace(R.id.fragment_container, fragment); 
     fragmentTransaction.commit(); 
     // Handle the camera action 

    } else if (id == R.id.nav_manage) {// 
     Bundle bundle = new Bundle();// 
     bundle.putInt("someStr",ID_OF_BEACH);// 
     //Set the fragment initially// 
     FragmentBeach fragment = new FragmentBeach();// 
     fragment.setArguments(bundle);// 
     FragmentTransaction fragmentTransaction =// 
       getSupportFragmentManager().beginTransaction();// 
     fragmentTransaction.replace(R.id.fragment_container, fragment);// 
     fragmentTransaction.commit();// 
     // Handle the camera action 

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

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

    } 

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

正如你可以看到，如果我们推第一个菜单if (id == R.id.nav_camara)它会通过一个JSONArray到片段类，它需要4-5秒加载。因此，如果用户每次进入nav_camara时都在菜单之间导航，则会使应用程序停留4秒，并且每次我们选择菜单项时都会重新创建片段的副本，因此即使我制作：setRetainInstance(true);在我的片段类中它不会工作。

您建议什么解决方案，以防止应用程序每次我们选择一个菜单项时重新创建一个新的片段？

Answer 1

你需要保持SparseArray<Fragment>保持实例在内存中。

遵循以下步骤：

1. 在你的活动创建一个字段：

   SparseArray<Fragment> myFragments; 
   

2. 初始化它在onCreate()，如：

   myFragments = new SparseArray<Fragment>(); 
   

3. 更新您的onNavigationItemSelected()：

   @Override 
   public boolean onNavigationItemSelected(MenuItem item) { 
       // Handle navigation view item clicks here. 
       int id = item.getItemId(); 
   
       if (id == R.id.nav_camara) { 
        // get cached instance of the fragment 
        fragment = myFragments.get(INT_CONSTANT_FOR_CAM_FRAGMENT); 
   
        // if fragment doesn't exist in myFragments, create one and add to it 
        if (fragment == null) { 
         fragment = new MainFragment(); 
         myFragments.put(INT_CONSTANT_FOR_CAM_FRAGMENT, fragment); 
        } 
   
        // now load the fragment 
        FragmentTransaction fragmentTransaction = 
           getSupportFragmentManager().beginTransaction(); 
        fragmentTransaction.replace(R.id.fragment_container, fragment); 
        fragmentTransaction.commit(); 
   
       } 
       // do the rest with others as well. 
   } 
   

4. 将AsyncTask移动到您的MainFragment的onActivityCreated()或类似的生命周期方法中。

以上方式可以让你重用片段和移动逻辑到正确的位置（你的活动应该不知道怎么MainFragment数据加载到启动本身，当然你仍然可以保持它的存在，但不推荐）。

Answer 2

您可以在将新片段推送到容器时添加TAG。然后使用FragmentManager#findFragmentByTag查找以前添加了相同标记的任何片段。

 FragmentManager manager = getSupportFragmentManager(); 
     FragmentTransaction transaction = manager.beginTransaction(); 
     Fragment oldFragment = manager.findFragmentByTag(tag); 
     if (oldFragment != null) 
      transaction.replace(R.id.fragment_container, oldFragment, tag); 
     else 
      transaction.replace(R.id.fragment_container, newInstanceOfFragment, tag); 
     transaction.commit(); 

Answer 3

声明它们在全球

GalleryFragment galleryFrag = new GalleryFragment(); 
FragmentTransaction ft; 
FragmentManager fm; 

@Override 
protected void onCreate(Bundle savedInstanceState) { 
    ... 

    fm = getSupportFragmentManager(); 

    ... 
} 

然后在您的导航选择

@Override 
public boolean onNavigationItemSelected(MenuItem item) { 

// Handle navigation view item clicks here. 
int id = item.getItemId(); 

if (id == R.id.nav_search) { 
    ft = fm.beginTransaction(); 
    ft.replace(R.id.fragment_container, galleryFrag).commit(); 
} 

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