RecyclerView重新加载图像

Question

我创建了一个连接到OMDB并使用它的API来获取电影数据的小应用程序。 正如你在下面的电影中可以看到的那样，如果我滚动得非常快，我可以看到图像被重新填充。调试表明它们确实被重新下载。我应该提到，我不保留任何文件的物理副本。

这是否被认为是正常行为或我错过了什么？

链接： https://youtu.be/2dO3XwGd5g8

RecyclerView类

package com.example.themoviekeeper.ui; 

import android.app.Activity; 
import android.support.v7.widget.RecyclerView; 
import android.view.LayoutInflater; 
import android.view.View; 
import android.view.ViewGroup; 
import android.widget.ImageView; 
import android.widget.TextView; 

import com.example.themoviekeeper.R; 
import com.example.themoviekeeper.db.MyMovie; 
import com.example.themoviekeeper.networking.Task_DownloadImage; 

import java.util.ArrayList; 

/** 
* Created by Xcalibur on 30/12/2016. 
*/ 

public class RecyclerViewAdapter_Search extends RecyclerView.Adapter<RecyclerViewAdapter_Search.MyViewHolder>{ 

    private ArrayList<MyMovie> _list; 
    private Activity _activity; 
    private LayoutInflater inflater; 

    public RecyclerViewAdapter_Search(ArrayList<MyMovie> list, Activity activity) { 

     _list = list; 
     _activity = activity; 

     inflater = LayoutInflater.from(_activity); 
    } 

    @Override 
    public RecyclerViewAdapter_Search.MyViewHolder onCreateViewHolder(ViewGroup parent, int viewType) { 

     View view = inflater.inflate(R.layout.view_search, parent, false); 

     MyViewHolder holder = new MyViewHolder(view); 

     return holder; 
    } 

    @Override 
    public void onBindViewHolder(MyViewHolder holder, int position) { 

     String year = _list.get(position).getYear(); 
     String title = _list.get(position).getTitle(); 
     String type = _list.get(position).getType(); 
     String poster = _list.get(position).getPoster(); 

     holder.tv_year.setText(year); 
     holder.tv_type.setText(type); 
     holder.tv_title.setText(title); 

     Task_DownloadImage dlImage = new Task_DownloadImage(_activity,holder); 
     String [] imageUrl ={poster}; 
     dlImage.execute(imageUrl); 


    } 


    @Override 
    public int getItemCount() { 
     return _list.size(); 
    } 

    public class MyViewHolder extends RecyclerView.ViewHolder { 

     TextView tv_year,tv_title,tv_type; 
     public ImageView iv_poster; 

     public MyViewHolder(View itemView) { 
      super(itemView); 

      tv_title = (TextView)itemView.findViewById(R.id.tv_title_searchview); 
      tv_type = (TextView)itemView.findViewById(R.id.tv_type_searchview); 
      tv_year = (TextView)itemView.findViewById(R.id.tv_year_searchview); 
      iv_poster = (ImageView)itemView.findViewById(R.id.iv_searchview); 

     } 

    } 


} 

的AsyncTask执行实际图像下载

package com.example.themoviekeeper.networking; 

import android.app.Activity; 
import android.app.ProgressDialog; 
import android.graphics.Bitmap; 
import android.graphics.BitmapFactory; 
import android.os.AsyncTask; 
import android.util.Log; 
import android.view.View; 
import android.widget.ImageView; 
import android.widget.TextView; 

import com.example.themoviekeeper.R; 
import com.example.themoviekeeper.ui.RecyclerViewAdapter_Search; 

import java.io.ByteArrayOutputStream; 
import java.io.InputStream; 
import java.net.HttpURLConnection; 
import java.net.URL; 

/** 
* Created by Xcalibur on 30/12/2016. 
*/ 

public class Task_DownloadImage extends AsyncTask<String, Integer,Bitmap> 
{ 

    private Activity mActivity; 
    private ProgressDialog mDialog; 
    private RecyclerViewAdapter_Search.MyViewHolder mHolder; 

    public Task_DownloadImage(Activity activity, RecyclerViewAdapter_Search.MyViewHolder holder) { 

     mHolder = holder; 
     mActivity = activity; 
     mDialog = new ProgressDialog(mActivity); 
    } 

    protected Bitmap doInBackground(String... urls) { 
     Log.d("doInBackground", "starting download of image"); 
     Bitmap image = downloadImage(urls[0]); 
     return image; 
    } 

    protected void onPreExecute() { 
     //ImageView imageView = (ImageView) mActivity.findViewById(R.id.imageView); 
     //imageView.setImageBitmap(null); 
     // Reset the progress bar 
//  mDialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL); 
//  mDialog.setCancelable(true); 
//  mDialog.setMessage("Loading..."); 
//  mDialog.setProgress(0); 
     //TextView errorMsg = (TextView) mActivity.findViewById(R.id.textView); 
     //errorMsg.setVisibility(View.INVISIBLE); 
    } 

    protected void onProgressUpdate(Integer... progress) { 
//  mDialog.show(); 
//  mDialog.setProgress(progress[0]); 
    } 

    protected void onPostExecute(Bitmap result) { 

     if (result != null) { 
      mHolder.iv_poster.setImageBitmap(result); 
//   ImageView imageView = (ImageView)mActivity.findViewById(R.id.imageView); 
//   imageView.setImageBitmap(result); 
     } 
     else { 
//   TextView errorMsg = (TextView)mActivity.findViewById(R.id.textView); 
//   errorMsg.setVisibility(View.VISIBLE); 
//   errorMsg.setText("Problem downloading image. Try again later"); 
     } 
     // Close the progress dialog 
     //mDialog.dismiss(); 
    } 

    private Bitmap downloadImage(String urlString) { 
     URL url; 
     try { 
      url = new URL(urlString); 
      HttpURLConnection httpCon = (HttpURLConnection) url.openConnection(); 
      InputStream is = httpCon.getInputStream(); 
      int fileLength = httpCon.getContentLength(); 
      ByteArrayOutputStream buffer = new ByteArrayOutputStream(); 
      int nRead, totalBytesRead = 0; 
      byte[] data = new byte[2048]; 
      mDialog.setMax(fileLength); 
      // Read the image bytes in chunks of 2048 bytes 
      while ((nRead = is.read(data, 0, data.length)) != -1) { 
       buffer.write(data, 0, nRead); 
       totalBytesRead += nRead; 
       publishProgress(totalBytesRead); 
      } 
      buffer.flush(); 
      byte[] image = buffer.toByteArray(); 
      Bitmap bitmap = BitmapFactory.decodeByteArray(image, 0, image.length); 
      return bitmap; 
     } catch (Exception e) { 
      e.printStackTrace(); 
     } 
     return null; 
    } 

} 

Answer 1

是的，这为e根据您的代码预计行为。 Android不会自动从HTTP请求中缓存下载的内容，因此每次滚动新回收的视图时都会重新下载其图像。

我建议您在代码中使用图像加载库，如Picasso或Glide，因为它们会自动缓存下载的图像并针对recyclerviews中的使用进行了优化。