Android将碎片保存到导航抽屉中

Question

在我的程序中我有一些片段,我可以通过点击该代码替换每个片段.我的问题是:这些片段加载很少,点击每个片段后,从中创建新片段并在点击片段后再次加载.如何保存片段内容或状态并防止重新加载？

@Override
    public void onNavigationDrawerItemSelected(int position) {
        Fragment fragment = null;
        switch (position) {
            case 0:
                fragment = new InfoFragment();
                break;
            case 1:
                fragment = new ParentOtoFragment();
                break;
            case 2:
                fragment = new ParentProFragment();
                break;
            case 3:
                fragment = new SupportFragment();
                break;
            case 4:
                fragment = new AboutFragment();
                break;
        }
        if (fragment != null){
            FragmentManager fragmentManager = getSupportFragmentManager();
            FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
            fragmentTransaction.replace(R.id.container,fragment).commit();
        }
    }

更新后

在@Vikram Ezhil回复此主题之后我是首字母fragments并fragmentTAG进入构造函数并将@Vikram Ezhil代码更改为以下代码,我的问题解决了.

@Override
   public void onNavigationDrawerItemSelected(int position) {
       FragmentTransaction fragmentTransaction = getSupportFragmentManager().beginTransaction();
       fragmentTransaction.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_OPEN);

       if (getSupportFragmentManager().findFragmentByTag(fragmentTAGS[position]) == null) {
           fragmentTransaction.add(R.id.container, fragments[position], fragmentTAGS[position]);
       }
       for (int i = 0; i < fragments.length; i++) {
           if (i == position) {
               fragmentTransaction.show(fragments[i]);
           } else {
               if (getSupportFragmentManager().findFragmentByTag(fragmentTAGS[position]) != null) {
                   fragmentTransaction.hide(fragments[i]);
               }
           }
       }
       fragmentTransaction.commit();
   }

Answer 1

每次单击导航抽屉中的项目时,都要防止碎片从头开始重新创建

fragmentTransaction.add(R.id.container,fragment).commit();

代替

fragmentTransaction.replace(R.id.container,fragment).commit();

但是,添加片段而不是替换片段时需要一些额外的工作.

1. 您需要确保不会多次添加相同的片段.您可以放置​​片段TAG并在添加片段之前检查TAG是否存在.例,

   if (getFragmentManager().findFragmentByTag("fragment1_tag") == null)
   {
       fragmentTransaction.add(R.id.container, fragment1, "fragment1_tag");
   }
   

2. 您需要隐藏未显示的片段,因为当您开始添加片段时,它们将在屏幕上相互重叠.

   if (getFragmentManager().findFragmentByTag("fragment1_tag") != null)
   {
       fragmentTransaction.hide(fragment1);
   }
   

3. 每当要更新片段中的特定部分时,请使用接口方法.我不会深入研究这一点,因为这完全是一个不同的主题.

4. 一旦应用程序被Android操作系统杀死,确保你的碎片没有重叠,为其他应用程序分配内存(查看这篇文章了解更多信息).

还添加了一些建议 - 从上面的代码中,您只有一个片段变量,并为所有5个屏幕重新使用它.我建议你为5个屏幕分别设置片段变量并保存一个数组.

当你开始添加,隐藏,显示片段时,这样做的原因将更加容易和通用.例,

InfoFragment fragment1 = new InfoFragment();
ParentOtoFragment fragment2 = new ParentOtoFragment();
ParentProFragment fragment3 = new ParentProFragment();
SupportFragment fragment4 = new SupportFragment();
AboutFragment fragment5 = new AboutFragment();

Fragment[] fragments = new Fragment[]{fragment1,fragment2,fragment3,fragment4,fragment5};
String[] fragmentTAGS = new String[]{"fragment1_tag","fragment2_tag","fragment3_tag","fragment4_tag","fragment5_tag"};

现在使用上述内容,您可以根据从导航栏中单击的项目切换片段.

@Override
public void onNavigationDrawerItemSelected(int position) 
{
      // Add the fragments only once if array haven't fragment
      if (getFragmentManager().findFragmentByTag(fragmentTAGS[position]) == null)
      {
          fragmentTransaction.add(R.id.container,fragments[position],fragmentTAGS[position]);
      };

      // Hiding & Showing fragments
      for(int catx=0;catx<fragments.length;catx++)
      {
         if(catx == position)
         {
              fragmentTransaction.show(fragments[catx]);
         }
         else
         {
              // Check if the fragment is added and then hide it
              if (getFragmentManager().findFragmentByTag(fragmentTAGS[catx]) != null)
              {
                  fragmentTransaction.hide(fragments[catx]);
              };
         };
      };

      fragmentTransaction.commit();
};