图片的二次采样三级缓存策略

来源：互联网发布：php base64解码编辑：程序博客网时间：2024/05/18 09:28
在android开发过程中会经常的加载图片,如果图片过大的话有可能会造成OOM,所以对于图片我们需要做进一步的处理提高性能
首先对图片本身大小入手,即对图片进行二次采样

//实例化Options样式载体BitmapFactory.Options options = new BitmapFactory.Options();//将inJustDecodeBounds设置为true,解码的时候可以返回图片的尺寸options.inJustDecodeBounds = true;BitmapFactory.decodeFile(filePath, options);//图片宽度int outWidth = options.outWidth;//图片高度int outHeight = options.outHeight;//缩放比例int sampleSize = 1;while ((outWidth / sampleSize > destWidth) || (outHeight / sampleSize > destHeight)) {    sampleSize *= 2;}//将inJustDecodeBounds设置为false,返回bitmapoptions.inJustDecodeBounds = false;//设置图片缩放比例 options.inSampleSize = sampleSize;//设置色彩模式,默认值是ARGB_8888options.inPreferredConfig = Bitmap.Config.RGB_565;//生成采样图片Bitmap comBitmap = BitmapFactory.decodeFile(filePath, options);

上面是对图片的二次采样过程,下面我们要对图片加载进行三级缓存处理.三级缓存即去图片首先去内存里看是否有该图片,如果没有就查文件里是否有该图片,如果仍然没有我们需要去网络里查该图片.
package demo.liuchen.com.android25_lrucache;import android.graphics.Bitmap;import android.graphics.BitmapFactory;import android.os.Handler;import android.os.Message;import android.support.v4.util.LruCache;import android.support.v7.app.AppCompatActivity;import android.os.Bundle;import android.util.Log;import android.view.View;import android.widget.ImageView;import java.io.BufferedOutputStream;import java.io.File;import java.io.FileNotFoundException;import java.io.FileOutputStream;import java.net.HttpURLConnection;import java.net.MalformedURLException;import java.net.URL;/** * 图片的三级缓存：LruCache--SDCard——Internet */public class MainActivity extends AppCompatActivity {    private String url = "http://p8.qhimg.com/t0113125382f3c4141a.png";   // private String url = "http://t2.27270.com/uploads/tu/201606/32/k5xnewfzvz0.jpg";    private ImageView imageView;    private LruCache<String,Bitmap> lruCache;    private Handler handler = new Handler(){        @Override        public void handleMessage(Message msg) {            super.handleMessage(msg);            if (msg.what==1){                Bitmap bitmap = (Bitmap) msg.obj;                imageView.setImageBitmap(bitmap);            }        }    };    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        imageView = (ImageView) findViewById(R.id.image_Show);        //获取运行时内存        Long MaxSize = Runtime.getRuntime().maxMemory();        //初始化LruCache        lruCache = new LruCache<String, Bitmap>((int) (MaxSize/8)){            //key 从内存中取出或存入的对象的名字            //value 存取的对象            //return 返回对象的缓存            @Override            protected int sizeOf(String key, Bitmap value) {                return value.getByteCount();            }        };    }    public void Click(View view) {    //当用户需要图片是先到缓存中去取        Bitmap bitmap = lruCache.get(getName(url));        if (bitmap!= null){            imageView.setImageBitmap(bitmap);        }else {            //在文件中查找            Bitmap bitmap1 = getBitmapFromSDCard(getName(url));            if (bitmap1!= null){                imageView.setImageBitmap(bitmap1);                //如果图片在SD卡中找到，将图片放入缓存                lruCache.put(getName(url),bitmap1);            }else {                getBitmapFromNet();            }        }    }        //从网络获取    private void getBitmapFromNet() {        Log.e("TAG","在网络中获取");        new Thread(new Runnable() {            @Override            public void run() {                try {                    URL path = new URL(url);                    HttpURLConnection httpURLConn = (HttpURLConnection) path.openConnection();                    if (httpURLConn.getResponseCode() == 200){                        final Bitmap bitmap = BitmapFactory.decodeStream(httpURLConn.getInputStream());                        //将图片放入缓存中                        lruCache.put(getName(url),bitmap);                        //将bitmap存入当前文件的文件中                        SaveBitmapToSDCard(getName(url),bitmap);                        Message message = Message.obtain();                        message.what=1;                        message.obj=bitmap;                       handler.sendMessage(message);                    }                } catch (Exception e) {                    e.printStackTrace();                }            }        }).start();    }//将Bitmap存入sd卡中    private void SaveBitmapToSDCard(String name, Bitmap bitmap) {        BufferedOutputStream bos = null;        try {            bos = new BufferedOutputStream(new FileOutputStream(new File(getExternalCacheDir(),name)));            if (name.endsWith("png")||name.endsWith("PNG")){                //把bitmap存入SdCard中                bitmap.compress(Bitmap.CompressFormat.PNG,100,bos);            }else {                bitmap.compress(Bitmap.CompressFormat.JPEG,100,bos);            }        } catch (FileNotFoundException e) {            e.printStackTrace();        }    }//从sd卡中获取图片    private Bitmap getBitmapFromSDCard(String name) {      //  Log.e("TAG","从SD卡中获取图片");        Bitmap bitmap = BitmapFactory.decodeFile(getExternalCacheDir().getAbsolutePath()+ File.separator+name);        //在SD卡中取出的Bitmap进行二次采样，去出去后会将二次采样好的图片放入缓存中       // Bitmap bitmap = BitmapUtils.getBitmap(getExternalCacheDir().getAbsolutePath()+File.separator+name,100,100);        return  bitmap;    }    //获取Bitmap为Url的名字    public String getName(String url){       String name = url.substring(url.lastIndexOf("/")+1,url.length());        return name;    }}
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