从零开始编写图片加载库（四）之图片缓存MemoryCache

来源：互联网发布：xcode使用教程c语言编辑：程序博客网时间：2024/06/10 01:15

图片加载通过内存加载是最快的，然而手机的内存并不是取之不尽的，所以在开发过程中还需要注意就是内存的使用问题，本节将不涉及内存使用和优化问题，本节只介绍图片下载后从内存中加载。

第一步：编写MemoryCache类

package cn.sundroid.cache;import java.lang.ref.Reference;import java.lang.ref.WeakReference;import java.util.Collections;import java.util.HashMap;import java.util.Map;import android.graphics.Bitmap;public class WeakMemoryCache {    /**保存Bitmap的对象*/    private final Map<String, Reference<Bitmap>> softMap = Collections            .synchronizedMap(new HashMap<String, Reference<Bitmap>>());    /**     * 根据键获得Bitmap     * @param key 查询需要的键     * @return     */    public Bitmap get(String key) {        if (key == null) {            throw new NullPointerException("key == null");        }        Bitmap result = null;        Reference<Bitmap> reference = softMap.get(key);        if (reference != null) {            result = reference.get();        }        return result;    }    /**     *      * 保存Bitmap到内存     * @param key 键     * @param value 值     * @return     */    public boolean put(String key, Bitmap value) {        if (key == null || value == null) {            throw new NullPointerException("key == null || value == null");        }        softMap.put(key, new WeakReference<Bitmap>(value));        return false;    }    /**     * 根据key从内存中移除Bitmap对象     * @param key     * @return     */    public Bitmap remove(String key) {        Reference<Bitmap> bmpRef = softMap.remove(key);        return bmpRef == null ? null : bmpRef.get();    }    /**     * 清空操作     */    public void clear() {        softMap.clear();    }}

第二步：编写实现，下载图片后在handler里面接收更新UI通知，从cache里面取图片。

package cn.sundroid.loader;import java.io.IOException;import java.io.InputStream;import java.net.HttpURLConnection;import java.net.MalformedURLException;import java.net.URL;import cn.sundroid.cache.WeakMemoryCache;import android.app.Activity;import android.graphics.Bitmap;import android.graphics.BitmapFactory;import android.os.Bundle;import android.os.Handler;import android.util.Log;import android.widget.ImageView;public class MainActivity extends Activity {    private ImageView image;    private final String TAG = "ImageLoader";    private WeakMemoryCache cache = new WeakMemoryCache();    private final String IMAGE_CACHE_KEY = "image_cache_key";    private Handler handler = new Handler() {        public void handleMessage(android.os.Message msg) {            Bitmap bitmap = cache.get(IMAGE_CACHE_KEY);            Log.e(TAG, "get bitmap from memory cache");            image.setImageBitmap(bitmap);        };    };    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        image = (ImageView) findViewById(R.id.image);        new Thread(new Runnable() {            @Override            public void run() {                try {                    //网络连接                    HttpURLConnection connection = (HttpURLConnection) new URL(                            "http://pic5.nipic.com/20091228/2588536_142951087553_2.jpg")                            .openConnection();                    connection.setConnectTimeout(3 * 1000);                    connection.setReadTimeout(20 * 1000);                    //读取文件流                    InputStream is = connection.getInputStream();                    //通过BitmapFactory解码二进制字节流成Bitmap                    Bitmap bitmap = BitmapFactory.decodeStream(is);                    Log.e(TAG, "put bitmap into memory cache");                    cache.put(IMAGE_CACHE_KEY, bitmap);                    //发送一个消息给Handler用于更新消息                    handler.sendEmptyMessage(0x10);                } catch (MalformedURLException e) {                    e.printStackTrace();                } catch (IOException e) {                    e.printStackTrace();                }            }        }).start();    }}

效果图

源代码下载==>

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