Android Fragment 优化与切换

Fragment三个包

    1.android.app.Fragment
    2.android.app.v4.Fragment 向下兼容
    3.androidx.fragment.app.Fragment

Fragment 关键类

    1.FragmentManager 碎片化的管理类
    2.FragmentTransation 操作Fragment做一些事务

FragMent 切换方式

    1.replace 会重新走生命周期 用的较少
    2.show/hide

  

   

    

     

    
    

     

      private void showFragment(Fragment fragment) {
     
    
   

    

     

    
    

     
        
      if (fragment != 
      null) {
     
    
   

    

     

    
    

     

                  FragmentTransaction fragmentTransaction = getSupportFragmentManager().beginTransaction();
     
    
   

    

     

    
    

     

                  hideAllFragment(fragmentTransaction);
     
    
   

    

     

    
    

     

                  fragmentTransaction.show(fragment);
     
    
   

    

     

    
    

     

                  fragmentTransaction.commitAllowingStateLoss();
     
    
   

    

     

    
    

     

              }
     
    
   

    

     

    
    

     

          }
     
    
   

    

     

    
    

     
 
     
    
   

    

     

    
    

     
    
      private void hideAllFragment(FragmentTransaction fragmentTransaction) {
     
    
   

    

     

    
    

     
        
      if (mFraSquare != 
      null) {
     
    
   

    

     

    
    

     

                  fragmentTransaction.hide(mFraSquare);
     
    
   

    

     

    
    

     

              }
     
    
   

    

     

    
    

     
        
      if (mFraMe != 
      null) {
     
    
   

    

     

    
    

     

                  fragmentTransaction.hide(mFraMe);
     
    
   

    

     

    
    

     

              }
     
    
   

    

     

    
    

     
        
      if (mFraChat != 
      null) {
     
    
   

    

     

    
    

     

                  fragmentTransaction.hide(mFraChat);
     
    
   

    

     

    
    

     

              }
     
    
   

    

     

    
    

     
        
      if (mFraStar != 
      null) {
     
    
   

    

     

    
    

     

                  fragmentTransaction.hide(mFraStar);
     
    
   

    

     

    
    

     

              }
     
    
   

    

     

    
    

     

          }
     
    
  

Fragment 优化

    onAttachFragment 此方法防止重叠
    场景：当应用内存紧张的时候，系统会回收掉 Frament对象；
    再次进入的时候会重新创建Fragment，并非原来的对象，我们无法控制，导致重叠

  

   

    

     

    
    

     
    
      @Override
     
    
   

    

     

    
    

     
    
      public void onAttachFragment(Fragment fragment) {
     
    
   

    

     

    
    

     
        
      if (mFraStar != 
      null && fragment 
      instanceof StarFragment) {
     
    
   

    

     

    
    

     

                  mFraStar = (StarFragment) fragment;
     
    
   

    

     

    
    

     

              }
     
    
   

    

     

    
    

     
 
     
    
   

    

     

    
    

     
        
      if (mFraChat != 
      null && fragment 
      instanceof ChatFragment) {
     
    
   

    

     

    
    

     

                  mFraChat = (ChatFragment) fragment;
     
    
   

    

     

    
    

     

              }
     
    
   

    

     

    
    

     
 
     
    
   

    

     

    
    

     
        
      if (mFraMe != 
      null && fragment 
      instanceof MeFragment) {
     
    
   

    

     

    
    

     

                  mFraMe = (MeFragment) fragment;
     
    
   

    

     

    
    

     

              }
     
    
   

    

     

    
    

     
 
     
    
   

    

     

    
    

     
        
      if (mFraSquare != 
      null && fragment 
      instanceof SquareFragment) {
     
    
   

    

     

    
    

     

                  mFraSquare = (SquareFragment) fragment;
     
    
   

    

     

    
    

     

              }
     
    
   

    

     

    
    

     

          }