Reihenfolge der Bilder, die mit AsyncTask geladen werden, ändert sich beim Scrollen in ListView

Question

Ich verwende eine AsyncTask, um Bilder in meine ListView zu laden. Wenn ich die App starte, ändert sich die Reihenfolge der Bilder beim Scrollen. Ich vermute, dass die getView() -Methode möglicherweise fehlerhaft ist. Aber ich kann keinen Weg finden, das zu beheben.

Da ich relativ neu in Android bin, kann ich auch nicht viele Optionen erkunden.

Hier ist mein Code:

DisplayPlacements.java

package com.example.android.areainfo; 

import android.os.Bundle; 
import android.support.v7.app.AppCompatActivity; 
import android.widget.ListView; 

public class DisplayPlacements extends AppCompatActivity { 
    ListView listView; 

    private String[] imageURLArray = new String[]{ 
      "http://farm8.staticflickr.com/7315/9046944633_881f24c4fa_s.jpg", 
      "http://farm4.staticflickr.com/3777/9049174610_bf51be8a07_s.jpg", 
      "http://farm8.staticflickr.com/7324/9046946887_d96a28376c_s.jpg", 
      "http://farm3.staticflickr.com/2828/9046946983_923887b17d_s.jpg", 
      "http://farm4.staticflickr.com/3810/9046947167_3a51fffa0b_s.jpg", 
      "http://farm4.staticflickr.com/3773/9049175264_b0ea30fa75_s.jpg", 
      "http://farm4.staticflickr.com/3781/9046945893_f27db35c7e_s.jpg", 
      "http://farm6.staticflickr.com/5344/9049177018_4621cb63db_s.jpg", 
      "http://farm8.staticflickr.com/7307/9046947621_67e0394f7b_s.jpg", 
      "http://farm6.staticflickr.com/5457/9046948185_3be564ac10_s.jpg", 
      "http://farm4.staticflickr.com/3752/9046946459_a41fbfe614_s.jpg", 
      "http://farm8.staticflickr.com/7403/9046946715_85f13b91e5_s.jpg", 
      "http://farm8.staticflickr.com/7315/9046944633_881f24c4fa_s.jpg", 
      "http://farm4.staticflickr.com/3777/9049174610_bf51be8a07_s.jpg", 
      "http://farm8.staticflickr.com/7324/9046946887_d96a28376c_s.jpg", 
      "http://farm3.staticflickr.com/2828/9046946983_923887b17d_s.jpg", 
      "http://farm4.staticflickr.com/3810/9046947167_3a51fffa0b_s.jpg", 
      "http://farm4.staticflickr.com/3773/9049175264_b0ea30fa75_s.jpg", 
      "http://farm4.staticflickr.com/3781/9046945893_f27db35c7e_s.jpg", 
      "http://farm6.staticflickr.com/5344/9049177018_4621cb63db_s.jpg", 
      "http://farm8.staticflickr.com/7307/9046947621_67e0394f7b_s.jpg", 
      "http://farm6.staticflickr.com/5457/9046948185_3be564ac10_s.jpg", 
      "http://farm4.staticflickr.com/3752/9046946459_a41fbfe614_s.jpg", 
      "http://farm8.staticflickr.com/7403/9046946715_85f13b91e5_s.jpg"}; 
    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.activity_display_placements); 

     listView = (ListView) findViewById(R.id.listPlacements); 
     ImageAdapter imageAdapter = new ImageAdapter(this, R.layout.row, imageURLArray); 
     listView.setAdapter(imageAdapter); 
    } 
} 

activity_display_placements.xml

<?xml version="1.0" encoding="utf-8"?> 
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" 
    xmlns:app="http://schemas.android.com/apk/res-auto" 
    xmlns:tools="http://schemas.android.com/tools" 
    android:id="@+id/activity_display_placements" 
    android:layout_width="match_parent" 
    android:layout_height="match_parent" 
    android:orientation="vertical" 
    tools:context="com.example.android.areainfo.DisplayPlacements"> 



    <ListView 
     android:layout_width="match_parent" 
     android:layout_height="wrap_content" 
     android:id="@+id/listPlacements"> 

    </ListView> 
</LinearLayout> 

row.xml

<?xml version="1.0" encoding="utf-8"?> 
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" 
    android:orientation="horizontal" android:layout_width="match_parent" 
    android:layout_height="match_parent"> 

    <ImageView 
     android:id="@+id/testImage" 
     android:layout_width="75dp" 
     android:layout_height="75dp" 
     android:scaleType="centerCrop" /> 

</LinearLayout> 

ImageAdapter.java

package com.example.android.areainfo; 

import android.app.Activity; 
import android.content.Context; 
import android.graphics.Bitmap; 
import android.graphics.BitmapFactory; 
import android.os.AsyncTask; 
import android.util.Log; 
import android.view.LayoutInflater; 
import android.view.View; 
import android.view.ViewGroup; 
import android.widget.ArrayAdapter; 
import android.widget.ImageView; 

import java.io.IOException; 
import java.net.URL; 

/** 
* Created by User on 30-Jan-17. 
*/ 

public class ImageAdapter extends ArrayAdapter<String> { 
    private String[] imageURLArray; 
    private LayoutInflater inflater; 

    public ImageAdapter(Context context, int textViewResourceId, 
         String[] imageArray) { 
     super(context, textViewResourceId, imageArray); 
     // TODO Auto-generated constructor stub 

     inflater = ((Activity)context).getLayoutInflater(); 
     imageURLArray = imageArray; 
    } 

    private static class ViewHolder { 
     String imageURL; 
     ImageView imageView; 
     Bitmap bitmap; 
    } 

    @Override 
    public View getView(int position, View convertView, ViewGroup parent) { 
     // TODO Auto-generated method stub 
     ViewHolder viewHolder = null; 
     if(convertView == null) { 
      convertView = inflater.inflate(R.layout.row, null); 

      viewHolder = new ViewHolder(); 
      viewHolder.imageView = (ImageView)convertView.findViewById(R.id.testImage); 
      convertView.setTag(viewHolder); 
     } 

     viewHolder = (ViewHolder)convertView.getTag(); 
     viewHolder.imageURL = imageURLArray[position]; 
     new DownloadAsyncTask().execute(viewHolder); 
     return convertView; 
    } 

    private class DownloadAsyncTask extends AsyncTask<ViewHolder, Void, ViewHolder> { 

     @Override 
     protected ViewHolder doInBackground(ViewHolder... params) { 
      // TODO Auto-generated method stub 
      //load image directly 
      ViewHolder viewHolder = params[0]; 
      try { 
       URL imageURL = new URL(viewHolder.imageURL); 
       viewHolder.bitmap = BitmapFactory.decodeStream(imageURL.openStream()); 
      } catch (IOException e) { 
       // TODO: handle exception 
       Log.e("error", "Downloading Image Failed"); 
       viewHolder.bitmap = null; 
      } 

      return viewHolder; 
     } 

     @Override 
     protected void onPostExecute(ViewHolder result) { 
      // TODO Auto-generated method stub 
      if (result.bitmap == null) { 
       // result.imageView.setImageResource(R.drawable.postthumb_loading); 
      } else { 
       result.imageView.setImageBitmap(result.bitmap); 
      } 
     } 
    } 
} 

Hilfe geschätzt.

Danke!

Answer 1

Sie sollten stattdessen RecyclerView verwenden. Es ist nicht das Hauptproblem hier, aber Recyclerview ist eine optimierte Art, Listen zu füllen.

Sie können ein gutes Beispiel finden here

und Bilder mit einer Bildlade Bibliothek wie glide verwenden zu laden oder Picasso es viel einfacher ist, die Dinge auf diese Weise zu tun.

können Sie ein gutes vollständiges Beispiel finden here