LruCache图片缓存

app一旦退出了，从新进入，缓存就没了。这里缓存只用于app不退出，多次加载时，只需加载一次。

逻辑类：

import okhttp3.Call;
import okhttp3.Callback;
import okhttp3.OkHttpClient;
import okhttp3.Request;
import okhttp3.Response;

/**
 * 核心：LruCache图片缓存
 * Created by liuyan on 2018/9/10.
 * 该类用来加载网络图片，并缓存到本地和内存
 */
//单例模式
public class SimpleImageLoader {
    private Handler handler = new Handler(Looper.getMainLooper());
    private static SimpleImageLoader mLoader;
    private LruCache<String,Bitmap> mLrucache;
    public static SimpleImageLoader getInstance(){
        if (mLoader == null){
            synchronized(SimpleImageLoader.class){
                if (mLoader == null){
                    mLoader = new SimpleImageLoader();
                }
            }
        }
        return mLoader;
    }
    //用来初始化缓存对象
    private SimpleImageLoader(){
        int maxSize = (int) (Runtime.getRuntime().maxMemory() / 8); //把应用最大内存除以8大小用于缓存
        mLrucache = new LruCache<String ,Bitmap>(maxSize){
            @Override
            protected int sizeOf(String key, Bitmap value) {
                return value.getByteCount();
            }
        };
    }
    //用来加载网络图片
    public void displayImage(ImageView view , String url){
        Bitmap bitmap = getBitmapFromCatch(url);
        if (bitmap != null && view != null){
            Log.i("TAG" , "从内存获取");
            view.setImageBitmap(bitmap);
            Log.i("TAG" , "结束1");
        }else {
            downloadImage(view , url);
        }
    }
    //从缓存中读取图片
    private Bitmap getBitmapFromCatch(String url){
        return mLrucache.get(url);
    }
    //将下载的图片保存到缓存中
    private void putBitmapToCache(Bitmap bitmap , String url){
        if (bitmap != null) {
            mLrucache.put(url, bitmap);
        }
    }
    //下载图片，并添加到缓存中去
    private void downloadImage(final ImageView imageView , final String url){
        OkHttpClient okHttpClient = new OkHttpClient();
        Request request = new Request.Builder()
                .url(url)
                .build();
        Call call = okHttpClient.newCall(request);
        call.enqueue(new Callback() {
            @Override
            public void onFailure(Call call, IOException e) {
                Log.i("TAG" ,"加载图片失败   " + "所在线程：" + Thread.currentThread().getName());
            }

            @Override
            public void onResponse(Call call, Response response) throws IOException {
                Log.i("TAG" , "下载图片所在线程：" + Thread.currentThread().getName());
                Bitmap bitmap = BitmapFactory.decodeStream(response.body().byteStream());
                if (bitmap != null){
                    putBitmapToCache(bitmap , url);
                    if (getBitmapFromCatch(url) != null){
                        if (imageView != null){
                            handler.post(new Runnable() {
                                @Override
                                public void run() {
                                    Log.i("TAG" , "run所在线程：" + Thread.currentThread().getName());
                                    imageView.setImageBitmap(getBitmapFromCatch(url));
                                    Log.i("TAG" , "结束2");
                                }
                            });
                        }
                    }
                }
            }
        });
    }




}