Android androidx下的fragment懒加载

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最新推荐文章于 2024-08-24 12:46:05 发布

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分类专栏： android 四大组件文章标签： android fragment

本文链接：https://blog.youkuaiyun.com/StudyOfAndroid/article/details/108851275

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在Androidx下，fragment的onHiddenChanged不再被调用，影响了懒加载的实现。文章介绍了如何通过在onResume中判断fragment的可见性来实现懒加载，并探讨了fragment内部嵌套fragment时的处理策略，强调了只创建一次fragment的重要性，提供了相应的代码示例和测试结果。

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androidx下的fragment中onHiddenChanged方法不会被调用，这就导致了懒加载实现方式要变更
前置条件：

BottomNavigationView+ViewPager+fragment
FragmentPagerAdapter pagerAdapter = new FragmentPagerAdapter(getSupportFragmentManager(),FragmentPagerAdapter.BEHAVIOR_RESUME_ONLY_CURRENT_FRAGMENT)

说明一下behavior的值：

BEHAVIOR_SET_USER_VISIBLE_HINT：使用这个创建的时候，当当前页面fragment可见不可见的时候setUserVisibleHint方法会被调用，
也就是我们之前的懒加载方法仍然可以使用，只是目前setUserVisibleHint这个方法被取消了，不建议使用，所以创建时候这个也不建议使用
BEHAVIOR_RESUME_ONLY_CURRENT_FRAGMENT：只有当前的fragment可见的时候，才会调用onResume方法，其他的只会调用到onStart方法

创建adapter对象，传入了behavior

这里不同fragment切换时候，只有在显示的时候才会调用onResum方法，所以只需要在onResume中判断是否可见就可以了，具体代码如下：

public abstract class BaseFragment extends Fragment {

    /**
     * 表示是否已经加载过了
     */
    private boolean isLoaded = false;
    /**
     * 表示是否可见
     */
    private boolean isVisible = false;

    @Override
    public void onResume() {
        super.onResume();
        isVisible = true;
        judzyLoadData();
    }

    private void judzyLoadData(){
        if (!isLoaded && isVisible){
            loadData();
            isLoaded = true;
        }
    }

    @Override
    public void onDestroy() {
        super.onDestroy();
        isVisible = false;
        isLoaded = false;
    }

    public abstract void loadData();
}

实际测试有效，只会调用一次
在这里插入图片描述
fragment内部嵌套fragment情况也测试了一下
三个主Fragment：HomeFragment、DashboardFragment、NotificationsFragment；在HomeFragment中嵌套3个MyFragment，测试懒加载方法，但是如果HomeFragment内部创建子Fragment方式一样，就会导致调用onCreateView方法，重新创建ViewPager和内部Fragment，所以需要只创建一次fragment

原来Activity中实现方法：

public class FragmentTestActivity1 extends AppCompatActivity {

    private BottomNavigationView bottomNavigationView;
    private ViewPager viewPager;
    private List<Fragment> fragments;
    private List<String> titles;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_fragment_test1);
        bottomNavigationView = findViewById(R.id.bottom_navigation);
        viewPager =findViewById(R.id.pager);

        fragments = new ArrayList<>();
        titles = new ArrayList<>();

        fragments.add(new HomeFragment("homeFragment1"));
        titles.add("homeFragment1");
        fragments.add(new DashboardFragment("DashboardFragment2"));
        titles.add("DashboardFragment2");
        fragments.add(new NotificationsFragment("NotificationsFragment3"));
        titles.add("NotificationsFragment3");
//        fragments.add(DashboardFragment.instantiate(this,DashboardFragment.class.getName()));
//        titles.add("DashboardFragment4");
        FragmentPagerAdapter pagerAdapter = new FragmentPagerAdapter(getSupportFragmentManager(),FragmentPagerAdapter.BEHAVIOR_RESUME_ONLY_CURRENT_FRAGMENT) {
            @NonNull
            @Override
            public Fragment getItem(int position) {
                return fragments.get(position);
            }

            @Override
            public int getCount() {
                return fragments.size();
            }
        };

//        TopAdapter adapter = new TopAdapter(getSupportFragmentManager(),fragments,titles);
        viewPager.setAdapter(pagerAdapter);


//        bottomNavigationView.removeAllViews();
        Menu menu = bottomNavigationView.getMenu();
//        menu.clear();
        for (int i = 0; i < menu.size(); i++) {
//            MenuItem item = menu.add(titles.get(i));
            MenuItem item = menu.getItem(i);
            View inflate = LayoutInflater.from(this).inflate(R.layout.activity_tab_item, null);
            TextView tabItem = inflate.findViewById(R.id.tv_tab_item);
            tabItem.setText(titles.get(i));
            item.setActionView(inflate);
        }


        bottomNavigationView.setOnNavigationItemSelectedListener(new BottomNavigationView.OnNavigationItemSelectedListener() {
            @Override
            public boolean onNavigationItemSelected(@NonNull MenuItem menuItem) {
                View customView = menuItem.getActionView();
                TextView tabItem = customView.findViewById(R.id.tv_tab_item);
                tabItem.setBackgroundColor(Color.parseColor("#ff5500"));
                switch (menuItem.getItemId()){
                    case R.id.navigation_home:
                        viewPager.setCurrentItem(0);
                        break;
                    case R.id.navigation_dashboard:
                        viewPager.setCurrentItem(1);
                        break;
                    case R.id.navigation_notifications:
                        viewPager.setCurrentItem(2);
                        break;
//                    case R.id.navigation_notifications2:
//                        viewPager.setCurrentItem(3);
//                        break;

                }
                return true;
            }
        });

        viewPager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {
            @Override
            public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {

            }

            @Override
            public void onPageSelected(int position) {
                MenuItem item = bottomNavigationView.getMenu().getItem(position);
                item.setChecked(true);
                View customView = item.getActionView();
                TextView tabItem = customView.findViewById(R.id.tv_tab_item);
                tabItem.setBackgroundColor(Color.parseColor("#ff5500"));
            }

            @Override
            public void onPageScrollStateChanged(int state) {

            }
        });

    }
}

在HomeFragment实现方法就要变更为：重点就是两个存储链表，只新建一次，后续只复用，无需创建新的对象，上面的懒加载方式就可以直接使用了，无需进行任何更改

public class HomeFragment extends BaseFragment {

    private TabLayout tabLayoutFragment;
    private ViewPager pagerFragment;
    private List<Fragment> fragments;
    private List<String> titles;
    
    private String name;

    private boolean isLoaded = false;

    public HomeFragment(String fName){
        this.name = fName;
    }

    public View onCreateView(@NonNull LayoutInflater inflater,
                             ViewGroup container, Bundle savedInstanceState) {
        View root = inflater.inflate(R.layout.fragment_home, container, false);
        Log.e(TAG,name + ":::::onCreateView");
        if (!isLoaded) {
            fragments = new ArrayList<>();
            titles = new ArrayList<>();
            fragments.add(new MyFragment("MyFragment1"));
            titles.add("MyFragment");
            fragments.add(new MyFragment("MyFragment2"));
            titles.add("MyFragment2");
            fragments.add(new MyFragment("MyFragment3"));
            titles.add("MyFragment3");
            isLoaded = true;
        }

        init(root);
        return root;
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        Log.e(TAG,name + ":::::onCreate");

    }

    @Override
    public void loadData() {
        Log.e(TAG,name + "::::loadData");
    }

    private void init(View root) {
        Log.e(TAG,name + "::::init");

        tabLayoutFragment = root.findViewById(R.id.table_fragment);
        pagerFragment = root.findViewById(R.id.pager_fragment);

        FragmentPagerAdapter pagerAdapter = new FragmentPagerAdapter(this.getChildFragmentManager(),FragmentPagerAdapter.BEHAVIOR_RESUME_ONLY_CURRENT_FRAGMENT) {
            @NonNull
            @Override
            public Fragment getItem(int position) {
                return fragments.get(position);
            }

            @Override
            public int getCount() {
                return fragments.size();
            }
        };

        pagerFragment.setAdapter(pagerAdapter);
        tabLayoutFragment.setupWithViewPager(pagerFragment);


        tabLayoutFragment.removeAllTabs();
        for (int i = 0; i < titles.size(); i++) {
            TabLayout.Tab tab = tabLayoutFragment.newTab();
            View inflate = LayoutInflater.from(this.getActivity()).inflate(R.layout.activity_tab_item, null);
            TextView tabItem = inflate.findViewById(R.id.tv_tab_item);
            tabItem.setText(titles.get(i));
            tab.setCustomView(inflate);
            tabLayoutFragment.addTab(tab);
        }

//        tabLayout.addTab(tabLayout.newTab().setText(titles.get(0)));
//        tabLayout.addTab(tabLayout.newTab().setText(titles.get(1)));
//        tabLayout.addTab(tabLayout.newTab().setText(titles.get(2)));

        tabLayoutFragment.addOnTabSelectedListener(new TabLayout.OnTabSelectedListener() {
            @Override
            public void onTabSelected(TabLayout.Tab tab) {
                View customView = tab.getCustomView();
                TextView tabItem = customView.findViewById(R.id.tv_tab_item);
                tabItem.setBackgroundColor(Color.parseColor("#ff5500"));
                pagerFragment.setCurrentItem(tab.getPosition());
                Fragment fragment = fragments.get(pagerFragment.getCurrentItem());
                fragment.onHiddenChanged(false);

            }

            @Override
            public void onTabUnselected(TabLayout.Tab tab) {
                View customView = tab.getCustomView();
                TextView tabItem = customView.findViewById(R.id.tv_tab_item);
                tabItem.setBackgroundColor(Color.parseColor("#ffffff"));
            }

            @Override
            public void onTabReselected(TabLayout.Tab tab) {
                View customView = tab.getCustomView();
                TextView tabItem = customView.findViewById(R.id.tv_tab_item);
                tabItem.setBackgroundColor(Color.parseColor("#ff5500"));
                pagerFragment.setCurrentItem(tab.getPosition());
            }
        });
        tabLayoutFragment.getTabAt(0).select();
    }
    @Override
    public void onDestroy() {
        super.onDestroy();
        Log.e(TAG,name + ":::::onDestroy");
        isLoaded = false;
    }

}