Android开发 FragmentManage的详解

最新推荐文章于 2025-03-04 00:19:04 发布

原创最新推荐文章于 2025-03-04 00:19:04 发布 · 48 阅读

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#android

本文详细解析了Android中FragmentManage的API功能，包括如何获取FragmentManage、findFragmentByTag和findFragmentById的区别、实例状态保存及其它关键方法的使用。

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前言

　　我还在学习Android开发的时候发过一篇简单的入门Fragment demo代码：https://www.cnblogs.com/guanxinjing/p/9708626.html 但是，Fragment远远不是一个简单的Demo就能了解清楚的，所以此篇博客将讲解FragmentManage的Api的功能

如何获取FragmentManage

activity里获取FragmentManage方式如下：

@Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState); setContentView(R.layout.activity_demo); FragmentManager fragmentManager = getSupportFragmentManager(); }

FragmentManage的API

findFragmentByTag

    private void addAndFind() {
        FragmentManager fragmentManager = getSupportFragmentManager();
        FragmentTransaction transaction = fragmentManager.beginTransaction();
        transaction.add(R.id.frameLayout, new OneFragment(), "one"); //添加容器布局id/ Fragment/ tag
        transaction.add(R.id.frameLayout, new TwoFragment(), "two");
        transaction.commitNow();//commitNow()为立即提交， 如果使用commit()提交可能会导致下面findFragmentByTag获取的Fragment为空
        Fragment fragment = fragmentManager.findFragmentByTag("one"); //查找指定tag的Fragment
        Log.e(TAG, "fragments size = " + fragmentManager.getFragments().size());
        Log.e(TAG, "Fragment id = " + fragment.getId());
        Log.e(TAG, "Fragment tag = " + fragment.getTag());
        Log.e(TAG, "Fragment name = " + fragment.getClass().getName());

    }

结果日志：

2020-02-24 10:39:22.838 5148-5148/com.zh.fragmentdemo E/com.zh.fragmentdemo.MainActivity: fragments size = 2
2020-02-24 10:39:22.838 5148-5148/com.zh.fragmentdemo E/com.zh.fragmentdemo.MainActivity: Fragment id = 2131230838
2020-02-24 10:39:22.838 5148-5148/com.zh.fragmentdemo E/com.zh.fragmentdemo.MainActivity: Fragment tag = one
2020-02-24 10:39:22.838 5148-5148/com.zh.fragmentdemo E/com.zh.fragmentdemo.MainActivity: Fragment name = com.zh.fragmentdemo.OneFragment

findFragmentById

请注意使用findFragmentById，只会查找到指定布局最后一个添加的Fragment(栈中最上面的Fragment)

    private void addAndFindById() {
        FragmentManager fragmentManager = getSupportFragmentManager();
        FragmentTransaction transaction = fragmentManager.beginTransaction();
        transaction.add(R.id.frameLayout, new OneFragment(), "one");
        transaction.add(R.id.frameLayout, new TwoFragment(), "two");
        transaction.commitNow();
        Fragment fragment1 = fragmentManager.findFragmentById(R.id.frameLayout);  //使用容器布局id查找,只会找到栈最后添加的Fragment
        Log.e(TAG, "1 Fragments size = " + fragmentManager.getFragments().size());
        Log.e(TAG, "1 Fragment id = " + fragment1.getId());
        Log.e(TAG, "1 Fragment tag = " + fragment1.getTag());
        Log.e(TAG, "1 Fragment name = " + fragment1.getClass().getName());
        FragmentTransaction transaction2 = fragmentManager.beginTransaction(); //FragmentTransaction每次调用commit后,就需要重新获取一个
        transaction2.remove(fragment1); //移除上面获取到的Fragment
        transaction2.commitNow();       //立即提交
        Fragment fragment2 = fragmentManager.findFragmentById(R.id.frameLayout);
        Log.e(TAG, "2 Fragments size = " + fragmentManager.getFragments().size());
        Log.e(TAG, "2 Fragment id = " + fragment2.getId());
        Log.e(TAG, "2 Fragment tag = " + fragment2.getTag());
        Log.e(TAG, "2 Fragment name = " + fragment2.getClass().getName());

    }

结果日志：

2020-02-24 11:23:25.052 5931-5931/com.zh.fragmentdemo E/com.zh.fragmentdemo.MainActivity: 1 Fragments size = 2
2020-02-24 11:23:25.052 5931-5931/com.zh.fragmentdemo E/com.zh.fragmentdemo.MainActivity: 1 Fragment id = 2131230838
2020-02-24 11:23:25.052 5931-5931/com.zh.fragmentdemo E/com.zh.fragmentdemo.MainActivity: 1 Fragment tag = two
2020-02-24 11:23:25.052 5931-5931/com.zh.fragmentdemo E/com.zh.fragmentdemo.MainActivity: 1 Fragment name = com.zh.fragmentdemo.TwoFragment
2020-02-24 11:23:25.054 5931-5931/com.zh.fragmentdemo E/com.zh.fragmentdemo.MainActivity: 2 Fragments size = 1
2020-02-24 11:23:25.055 5931-5931/com.zh.fragmentdemo E/com.zh.fragmentdemo.MainActivity: 2 Fragment id = 2131230838
2020-02-24 11:23:25.055 5931-5931/com.zh.fragmentdemo E/com.zh.fragmentdemo.MainActivity: 2 Fragment tag = one
2020-02-24 11:23:25.055 5931-5931/com.zh.fragmentdemo E/com.zh.fragmentdemo.MainActivity: 2 Fragment name = com.zh.fragmentdemo.OneFragment