Android ViewPager2 load once when fast scroll many page，Java

痛定思痛。 2023-09-25 20:52 47阅读 0赞

<?xml version="1.0" encoding="utf-8"?>
    <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:tools="http://schemas.android.com/tools"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        tools:context=".MainActivity">
    
        <androidx.viewpager2.widget.ViewPager2
            android:id="@+id/viewpager"
            android:layout_width="match_parent"
            android:layout_height="match_parent" />
    
    </RelativeLayout>

import androidx.annotation.NonNull;
    import androidx.appcompat.app.AppCompatActivity;
    import androidx.fragment.app.Fragment;
    import androidx.fragment.app.FragmentActivity;
    import androidx.viewpager2.adapter.FragmentStateAdapter;
    import androidx.viewpager2.widget.ViewPager2;
    
    import android.os.Bundle;
    import android.util.Log;
    
    import java.util.ArrayList;
    import java.util.List;
    
    public class MainActivity extends AppCompatActivity {
        private String TAG = "fly";
    
        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main);
    
            ViewPager2 viewPager2 = findViewById(R.id.viewpager);
    
            final List<Fragment> fragments = new ArrayList<>();
            for (int i = 0; i < 999; i++) {
                Fragment fragment = new TestFrgment("fragment" + i);
                fragments.add(fragment);
            }
    
            MyFragmentAdapter adapter = new MyFragmentAdapter(this, fragments);
            viewPager2.setAdapter(adapter);
    
            viewPager2.registerOnPageChangeCallback(new LazyOnPageChangeCallback(){
                @Override
                public void selectedPage(int pos) {
                    pageSelected(pos);
                }
            });
        }
    
        private void pageSelected(int pos) {
            Log.d(TAG, "-");
            Log.d(TAG, "选中:" + pos);
            Log.d(TAG, "--");
        }
    
        private class MyFragmentAdapter extends FragmentStateAdapter {
            private List<Fragment> fragments;
    
            public MyFragmentAdapter(@NonNull FragmentActivity fragmentActivity, List<Fragment> list) {
                super(fragmentActivity);
                this.fragments = list;
            }
    
            @NonNull
            @Override
            public Fragment createFragment(int position) {
                return fragments.get(position);
            }
    
            @Override
            public int getItemCount() {
                return fragments.size();
            }
        }
    }

import android.os.Handler;
    import android.os.Looper;
    import android.os.Message;
    
    import androidx.annotation.NonNull;
    import androidx.viewpager2.widget.ViewPager2;
    
    public class LazyOnPageChangeCallback extends ViewPager2.OnPageChangeCallback {
        private long DELAY_TIME = 400L;
    
        private int mCurPos = 0;
    
        private int CHANGE_MSG_WHAT = 0xff01;
    
        public void selectedPage(int pos) {
    
        }
    
        private Handler mLoad = new Handler(Looper.getMainLooper()) {
            @Override
            public void handleMessage(@NonNull Message msg) {
                if (msg.what == CHANGE_MSG_WHAT) {
                    removeMessages(CHANGE_MSG_WHAT);
                    selectedPage(mCurPos);
                }
            }
        };
    
        @Override
        public void onPageSelected(int position) {
            super.onPageSelected(position);
            mCurPos = position;
            //viewpager首次加载触发selectedPage()
            mLoad.sendEmptyMessageDelayed(CHANGE_MSG_WHAT, DELAY_TIME);
        }
    
        @Override
        public void onPageScrollStateChanged(int state) {
            super.onPageScrollStateChanged(state);
            if (state == ViewPager2.SCROLL_STATE_DRAGGING) {
                mLoad.removeMessages(CHANGE_MSG_WHAT);
            } else if (state == ViewPager2.SCROLL_STATE_IDLE) {
                mLoad.sendEmptyMessageDelayed(CHANGE_MSG_WHAT, DELAY_TIME);
            }
        }
    }

import android.os.Bundle;
    import android.util.Log;
    import android.util.TypedValue;
    import android.view.LayoutInflater;
    import android.view.View;
    import android.view.ViewGroup;
    import android.widget.TextView;
    
    import androidx.annotation.NonNull;
    import androidx.annotation.Nullable;
    import androidx.core.content.ContextCompat;
    import androidx.fragment.app.Fragment;
    
    public class TestFrgment extends Fragment {
        private String tag;
    
        private String LOG = "生命周期->";
    
        public TestFrgment(String tag) {
            this.tag = tag;
        }
    
        @Override
        public void onCreate(@Nullable Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            Log.d(LOG + tag, "onCreate");
        }
    
        @Nullable
        @Override
        public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
            TextView text = new TextView(getContext());
            text.setText(tag);
            text.setTextSize(TypedValue.COMPLEX_UNIT_DIP, 80);
            text.setTextColor(ContextCompat.getColor(getContext(), android.R.color.holo_red_dark));
            return text;
        }
    
        @Override
        public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
            super.onViewCreated(view, savedInstanceState);
            Log.d(LOG + tag, "onViewCreated");
        }
    
        @Override
        public void onStart() {
            super.onStart();
            Log.d(LOG + tag, "onStart");
        }
    
        @Override
        public void onResume() {
            super.onResume();
            Log.d(LOG + tag, "onResume");
        }
    
        @Override
        public void onPause() {
            super.onPause();
            Log.d(LOG + tag, "onPause");
        }
    
        @Override
        public void onStop() {
            super.onStop();
            Log.d(LOG + tag, "onStop");
        }
    
        @Override
        public void onDestroy() {
            super.onDestroy();
            Log.d(LOG + tag, "onDestroy");
        }
    }

[ViewPager2和Fragment可见性及懒加载解决方案\_zhangphil的博客-CSDN博客ViewPager2和Fragment新的可见性及懒加载解决方案，旨在解决ViewPager（ViewPager2）只有当前Fragment唯一可见时候网络刷新或绘图。注意：过去的setUserVisibleHint()已被废弃，开发者不要再使用基于setUserVisibleHint()解决Fragment可见性和懒加载（或延迟加载）的场景。新方案用最新的ViewPager2替代过去旧版的ViewPager，再结合Fragment的resume和pause生命周期实现。写一个demo例子，测试的主类M![favicon32.ico][]https://blog.csdn.net/zhangphil/article/details/108893237][ViewPager2_Fragment_zhangphil_-CSDN_ViewPager2_Fragment_ViewPager_ViewPager2_Fragment_setUserVisibleHint_setUserVisibleHint_Fragment_ViewPager2_ViewPager_Fragment_resume_pause_demo_M_favicon32.ico_https_blog.csdn.net_zhangphil_article_details_108893237]

[favicon32.ico]: https://g.csdnimg.cn/static/logo/favicon32.ico
[ViewPager2_Fragment_zhangphil_-CSDN_ViewPager2_Fragment_ViewPager_ViewPager2_Fragment_setUserVisibleHint_setUserVisibleHint_Fragment_ViewPager2_ViewPager_Fragment_resume_pause_demo_M_favicon32.ico_https_blog.csdn.net_zhangphil_article_details_108893237]: https://blog.csdn.net/zhangphil/article/details/108893237