ListView异步加载网络图片
1.在新建的项目中加入如下权限：
<uses-permission android:name="android.permission.INTERNET"/>
2.MainActivity.java
import java.util.LinkedList; import android.app.Activity; import android.os.Bundle; import android.view.Menu; import android.widget.ListView; import com.example.loadimages.R; import com.lxw.adapter.ImageAdapter; import com.lxw.bean.Picture; public class MainActivity extends Activity { private ListView listview; private LinkedList<Picture> data; private ImageAdapter adapter; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); loadData(); listview = (ListView) findViewById(R.id.listview); adapter = new ImageAdapter(data, getLayoutInflater(), this); listview.setAdapter(adapter); } public void loadData() { if (data == null) data = new LinkedList<Picture>(); for (int i = 0; i < URLS.length; i++) { data.add(new Picture(URLS[i])); } } @Override public boolean onCreateOptionsMenu(Menu menu) { getMenuInflater().inflate(R.menu.main, menu); return true; } private static final String[] URLS = { 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3.ImageAdapter.java
package com.lxw.adapter; import java.util.LinkedList; import android.content.Context; import android.view.LayoutInflater; import android.view.View; import android.view.ViewGroup; import android.widget.BaseAdapter; import android.widget.ImageView; import com.example.loadimages.R; import com.lxw.bean.Picture; import com.lxw.manager.BitmapManager; public class ImageAdapter extends BaseAdapter { LinkedList<Picture> data = new LinkedList<Picture>(); LayoutInflater inflator; Context context; public ImageAdapter(LinkedList<Picture> data, LayoutInflater inflator, Context context) { this.data = data; this.inflator = inflator; this.context = context; } @Override public int getCount() { return data.size(); } @Override public Object getItem(int position) { return data.get(position); } @Override public long getItemId(int position) { return position; } @Override public View getView(int position, View convertView, ViewGroup parent) { ViewHolder holder; if (convertView == null) { convertView = inflator.inflate(R.layout.row, null); ImageView imageView = (ImageView) convertView .findViewById(R.id.image); holder = new ViewHolder(); holder.imageView = imageView; convertView.setTag(holder); } else { holder = (ViewHolder) convertView.getTag(); } Picture item = data.get(position); holder.imageView.setImageDrawable(this.context.getResources() .getDrawable(R.drawable.ic_launcher)); BitmapManager.INSTANCE.loadBitmap(item.getImageUrl(), holder.imageView, 300, 300); return convertView; } class ViewHolder { ImageView imageView; } }
4.BitmapManager.java
package com.lxw.manager; import java.io.IOException; import java.io.InputStream; import java.lang.ref.SoftReference; import java.net.MalformedURLException; import java.net.URL; import java.util.Collections; import java.util.HashMap; import java.util.Map; import java.util.WeakHashMap; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; import android.annotation.SuppressLint; import android.graphics.Bitmap; import android.graphics.BitmapFactory; import android.os.Handler; import android.os.Message; import android.util.Log; import android.widget.ImageView; public enum BitmapManager { INSTANCE; private final Map<String, SoftReference<Bitmap>> cache; private final ExecutorService pool; private Map<ImageView, String> imageViews = Collections .synchronizedMap(new WeakHashMap<ImageView, String>()); private Bitmap placeholder; BitmapManager() { cache = new HashMap<String, SoftReference<Bitmap>>(); pool = Executors.newFixedThreadPool(5); } public void setPlaceholder(Bitmap bmp) { placeholder = bmp; } public Bitmap getBitmapFromCache(String url) { if (cache.containsKey(url)) { return cache.get(url).get(); } return null; } @SuppressLint("HandlerLeak") public void queueJob(final String url, final ImageView imageView, final int width, final int height) { /* Create handler in UI thread. */ final Handler handler = new Handler() { @Override public void handleMessage(Message msg) { String tag = imageViews.get(imageView); if (tag != null && tag.equals(url)) { if (msg.obj != null) { imageView.setImageBitmap((Bitmap) msg.obj); } else { imageView.setImageBitmap(placeholder); Log.d(null, "fail " + url); } } } }; pool.submit(new Runnable() { @Override public void run() { final Bitmap bmp = downloadBitmap(url, width, height); Message message = Message.obtain(); message.obj = bmp; Log.d("domn", "Item downloaded:"); handler.sendMessage(message); } }); } public void loadBitmap(final String url, final ImageView imageView, final int width, final int height) { imageViews.put(imageView, url); Bitmap bitmap = getBitmapFromCache(url); // check in UI thread, so no concurrency issues if (bitmap != null) { Log.d(null, "Item loaded from cache: " + url); imageView.setImageBitmap(bitmap); } else { imageView.setImageBitmap(placeholder); queueJob(url, imageView, width, height); } } private Bitmap downloadBitmap(String url, int width, int height) { try { Bitmap bitmap = BitmapFactory.decodeStream((InputStream) new URL( url).getContent()); bitmap = Bitmap.createScaledBitmap(bitmap, width, height, true); cache.put(url, new SoftReference<Bitmap>(bitmap)); return bitmap; } catch (MalformedURLException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } Log.d("bitap", "null"); return null; } }
5.Picture.java
package com.lxw.bean; public class Picture { private String imageUrl; public Picture(String imageUrl) { this.imageUrl = imageUrl; } public String getImageUrl() { return imageUrl; } public void setImageUrl(String imageUrl) { this.imageUrl = imageUrl; } }
6.activity_main.xml
<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" > <ListView android:id="@+id/listview" android:layout_width="match_parent" android:layout_height="match_parent" /> </RelativeLayout>
7.row.xml
<?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent" android:layout_height="match_parent" android:orientation="vertical" > <ImageView android:id="@+id/image" android:layout_width="wrap_content" android:layout_height="wrap_content" android:contentDescription="@string/app_name" /> </LinearLayout>
8.运行!
