Androidx懒加载Fragment

我使用viewpager+fragment实现懒加载。代码如下：

1.fragment 

import android.content.Context;
import android.os.Bundle;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.fragment.app.Fragment;

/**
 * @author zsl
 * @date 2019/11/22.
 */
public abstract class LazyFragment extends Fragment {
   private View root;
   protected boolean isLoaded;


   @Override
   public void onCreate(@Nullable Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
   }

   @Override
   public void onAttach(@NonNull Context context) {
      super.onAttach(context);
   }

   @Override
   public void onActivityCreated(@Nullable Bundle savedInstanceState) {
      super.onActivityCreated(savedInstanceState);
   }

   @Nullable
   @Override
   public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
      if (root==null){
         root = inflater.inflate(getLayoutResource(),container,false);
      }

      isLoaded = false;

      initView(root);

      return root;
   }

   @Override
   public void onResume() {
      super.onResume();
      if (!isLoaded){
         lazyLoad(true);
      }
   }

   @Override
   public void onPause() {
      super.onPause();
      if (!isLoaded){
         lazyLoad(false);
      }
   }

   @Override
   public void onDestroy() {
      super.onDestroy();
   }

   protected void log(String s){
      Log.e("LazyFragment",s);
   }

   /**
    * 初始化资源控件
    *
    * @param view root
    */
   protected abstract void initView(View view);

   /**
    * 获取布局资源
    *
    * @return layout resource id
    */
   protected abstract int getLayoutResource();

   /**
    * 是否需要懒加载
    * @param startLoad  true 需要懒加载,false 不需要懒加载
    */
   protected void lazyLoad(boolean startLoad){}

   /**
    * 子类数据未获取，需要重新获取数据
    *
    * 如果需要重新获取，子类生命周期再次走到 onResume 时，会重新加载数据
    *
    * @param reload    是否需要重新获取
    */
   protected void loaded(boolean loaded){
      isLoaded = loaded;
      log("数据需要重新加载");
   }

}

 2.adapter

import java.util.List;

import androidx.annotation.NonNull;
import androidx.fragment.app.Fragment;
import androidx.fragment.app.FragmentManager;
import androidx.fragment.app.FragmentStatePagerAdapter;

/**
 * @author zsl
 * @date 2019/11/22.
 */
public class LazyFragmentAdapter extends FragmentStatePagerAdapter {
   private List<Fragment> items;

   public LazyFragmentAdapter(@NonNull FragmentManager fm, int behavior) {
      super(fm, behavior);
   }

   public void setItems(List<Fragment> list){
      this.items = list;
   }

   public List<Fragment> getItems() {
      return items;
   }

   @NonNull
   @Override
   public Fragment getItem(int position) {
      return items==null?null:items.get(position);
   }

   @Override
   public int getCount() {
      return items==null?0:items.size();
   }
}

3.使用：

import android.os.Bundle;

import com.zsl.appmarket.R;
import com.zsl.appmarket.app.ui.fragment.Fragmeng1;
import com.zsl.appmarket.app.ui.fragment.Fragmeng2;
import com.zsl.appmarket.app.ui.fragment.Fragmeng3;
import com.zsl.appmarket.app.ui.fragment.Fragmeng4;
import com.zsl.appmarket.app.ui.fragment.Fragmeng5;

import java.util.ArrayList;
import java.util.List;

import androidx.annotation.Nullable;
import androidx.appcompat.app.AppCompatActivity;
import androidx.fragment.app.Fragment;
import androidx.viewpager.widget.ViewPager;

import static androidx.fragment.app.FragmentStatePagerAdapter.BEHAVIOR_RESUME_ONLY_CURRENT_FRAGMENT;

/**
 * @author zsl
 * @date 2019/11/22.
 */
public class LazyFragmentTest extends AppCompatActivity {

   @Override
   protected void onCreate(@Nullable Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.activity_lazy_fragment);

      ViewPager vp = findViewById(R.id.vp);

      final LazyFragmentAdapter adapter = new LazyFragmentAdapter(getSupportFragmentManager(), BEHAVIOR_RESUME_ONLY_CURRENT_FRAGMENT);
      adapter.setItems(getItems());
      vp.setAdapter(adapter);

   }

   private List<Fragment> getItems() {
      ArrayList<Fragment> items = new ArrayList<>();
      items.add(Fragmeng1.newInstance());
      items.add(Fragmeng2.newInstance());
      items.add(Fragmeng3.newInstance());
      items.add(Fragmeng4.newInstance());
      items.add(Fragmeng5.newInstance());
      return items;
   }

 

4.自定义的viewpager：

 （由于原生的viewpager的高度不会随子item高度改变，即设置子item高度无效，所以自定义viewpager）

import android.content.Context;
import android.util.AttributeSet;
import android.view.View;
import android.view.ViewGroup;

import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.viewpager.widget.ViewPager;

/**
 * @author zsl
 * @date 2019/11/22.
 */
public class CustomViewPager extends ViewPager {
   public CustomViewPager(@NonNull Context context) {
      super(context);
   }

   public CustomViewPager(@NonNull Context context, @Nullable AttributeSet attrs) {
      super(context, attrs);
   }

   @Override
   protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
      int height = 0;
      for (int i = 0,len = getChildCount(); i < len; i++) {
         View child = getChildAt(i);
         ViewGroup.LayoutParams lp = child.getLayoutParams();
         int childWidth = getChildMeasureSpec(widthMeasureSpec, 0, lp.width);
         int childHeight = getChildMeasureSpec(heightMeasureSpec, 0, lp.height);
         child.measure(childWidth,childHeight);
         int measuredHeight = child.getMeasuredHeight();
         height = Math.max(measuredHeight,height);
      }
      heightMeasureSpec = View.MeasureSpec.makeMeasureSpec(height,MeasureSpec.EXACTLY);
      super.onMeasure(widthMeasureSpec, heightMeasureSpec);
      
   }
}

5.对于是需要懒加载，根据LazyFragment子类实际业务决定。

@Override
protected void lazyLoad(boolean startLoad) {
   log("Fragmeng1 lazyLoad:"+startLoad);

   //根据是否已经获取到数据，来传入true或false调用loader方法告知父类下次切换回来是否需要重新加载数据
   loaded(false);
}