图片加载框架－Picasso最详细的使用指南

   compile 'com.squareup.picasso:picasso:2.5.2'

Uri uri = Uri.parse(ANDROID_RESOURCE + context.getPackageName() + FOREWARD_SLASH + resourceId)
Picasso.with(this).load(uri).into(mImageView);

 Picasso.with(this).load(file).into(mImageView);

Picasso.with(this).load(R.mipmap.ic_launcher).into(mImageView);

/**
   * Start an image request using the specified path. This is a convenience method for calling
   * {@link #load(Uri)}.
   * <p>
   * This path may be a remote URL, file resource (prefixed with {@code file:}), content resource
   * (prefixed with {@code content:}), or android resource (prefixed with {@code
   * android.resource:}.
   * <p>
   * Passing {@code null} as a {@code path} will not trigger any request but will set a
   * placeholder, if one is specified.
   *
   * @see #load(Uri)
   * @see #load(File)
   * @see #load(int)
   * @throws IllegalArgumentException if {@code path} is empty or blank string.
   */
  public RequestCreator load(String path) {
    if (path == null) {
      return new RequestCreator(this, null, 0);
    }
    if (path.trim().length() == 0) {
      throw new IllegalArgumentException("Path must not be empty.");
    }
    return load(Uri.parse(path));
  }

 Picasso.with(this).load(URL)
                .placeholder(R.drawable.default_bg)
                .error(R.drawable.error_iamge)
                .resize(400,200)
                .into(mImageView);

 <dimen name="image_width">300dp</dimen>
 <dimen name="image_height">200dp</dimen>

 Picasso.with(this).load(URL)
                .placeholder(R.drawable.default_bg)
                .error(R.drawable.error_iamge)
                .resizeDimen(R.dimen.image_width,R.dimen.image_height)
                .into(mImageView);

  Picasso.with(this).load(URL)
                .placeholder(R.drawable.default_bg)
                .error(R.drawable.error_iamge)
                .resize(4000,2000)
                .onlyScaleDown()
                .into(mImageView);

 Picasso.with(this).load(URL)
                .placeholder(R.drawable.default_bg)
                .error(R.drawable.error_iamge)
                .resize(400,200)
                .centerInside()
                .into(mImageView);

Picasso.with(this).load(URL)
                .placeholder(R.drawable.default_bg)
                .error(R.drawable.error_iamge)
                .fit()
                .into(mImageView);

 Picasso.with(this).load(URL)
                .placeholder(R.drawable.default_bg)
                .error(R.drawable.error_iamge)
                .fit()
                .centerCrop()
                .into(mImageView);

 public static class BlurTransformation implements Transformation{
        RenderScript rs;
        public BlurTransformation(Context context) {
            super();
            rs = RenderScript.create(context);
        }
        @Override
        public Bitmap transform(Bitmap bitmap) {
            // Create another bitmap that will hold the results of the filter.
            Bitmap blurredBitmap = bitmap.copy(Bitmap.Config.ARGB_8888, true);
            // Allocate memory for Renderscript to work with
            Allocation input = Allocation.createFromBitmap(rs, blurredBitmap, Allocation.MipmapControl.MIPMAP_FULL, Allocation.USAGE_SHARED);
            Allocation output = Allocation.createTyped(rs, input.getType());
            // Load up an instance of the specific script that we want to use.
            ScriptIntrinsicBlur script = ScriptIntrinsicBlur.create(rs, Element.U8_4(rs));
            script.setInput(input);
            // Set the blur radius
            script.setRadius(25);
            // Start the ScriptIntrinisicBlur
            script.forEach(output);
            // Copy the output to the blurred bitmap
            output.copyTo(blurredBitmap);
            bitmap.recycle();
            return blurredBitmap;
        }
        @Override
        public String key() {
            return "blur";
        }
    }

  Picasso.with(this).load(URL)
                .placeholder(R.drawable.default_bg)
                .error(R.drawable.error_iamge)
                .transform(new BlurTransformation(this))
                .into(mBlurImage);

 public static class GrayTransformation implements Transformation{
        @Override
        public Bitmap transform(Bitmap source) {
            int width, height;
            height = source.getHeight();
            width = source.getWidth();
            Bitmap bmpGrayscale = Bitmap.createBitmap(width, height, Bitmap.Config.RGB_565);
            Canvas c = new Canvas(bmpGrayscale);
            Paint paint = new Paint();
            ColorMatrix cm = new ColorMatrix();
            cm.setSaturation(0);
            ColorMatrixColorFilter f = new ColorMatrixColorFilter(cm);
            paint.setColorFilter(f);
            c.drawBitmap(source, 0, 0, paint);
            if(source!=null && source!=bmpGrayscale){
                source.recycle();
            }
            return bmpGrayscale;
        }
        @Override
        public String key() {
            return "gray";
        }
    }

 Picasso.with(this).load(URL)
                .placeholder(R.drawable.default_bg)
                .error(R.drawable.error_iamge)
                .fit()
                .centerCrop()
                .transform(new GrayTransformation())//度灰处理
                .transform(new BlurTransformation(this))//高斯模糊
                .into(mBlurImage);

        List<Transformation> transformations = new ArrayList<>();
        transformations.add(new GrayTransformation());
        transformations.add(new BlurTransformation(this));
        Picasso.with(this).load(URL)
                .placeholder(R.drawable.default_bg)
                .error(R.drawable.error_iamge)
                .fit()
                .centerCrop()
                .transform(transformations)
                .into(mBlurImage);

public enum Priority {
    LOW,
    NORMAL,
    HIGH
  }

 Picasso.with(this).load(URL)
                .placeholder(R.drawable.default_bg)
                .error(R.drawable.error_iamge)
                .priority(Picasso.Priority.HIGH)
               // .priority(Picasso.Priority.LOW)
                .into(mImageView);

Picasso.with(this).load(mData.get(position))
                .placeholder(R.drawable.default_bg)
                .error(R.drawable.error_iamge)
                .tag("PhotoTag")
                .into(holder.mImageView);

 @Override
    protected void onDestroy() {
        super.onDestroy();
        Picasso.with(this).cancelTag("PhotoTag");
    }

 try {
           Bitmap bitmap =  Picasso.with(this).load(URL).get();
        } catch (IOException e) {
            e.printStackTrace();
        }

with(this).load(URL)
                .placeholder(R.drawable.default_bg)
                .error(R.drawable.error_iamge)
                .memoryPolicy(MemoryPolicy.NO_CACHE,MemoryPolicy.NO_STORE) //静止内存缓存
                .into(mBlurImage);

 with(this).load(URL)
                .placeholder(R.drawable.default_bg)
                .error(R.drawable.error_iamge)
                .memoryPolicy(MemoryPolicy.NO_CACHE,MemoryPolicy.NO_STORE)//跳过内存缓存
                .networkPolicy(NetworkPolicy.NO_CACHE)//跳过磁盘缓存
                .into(mBlurImage);

 /** Describes where the image was loaded from. */
  public enum LoadedFrom {
    MEMORY(Color.GREEN),
    DISK(Color.BLUE),
    NETWORK(Color.RED);
    final int debugColor;
    private LoadedFrom(int debugColor) {
      this.debugColor = debugColor;
    }
  }

   Picasso.with(this)
          .setLoggingEnabled(true);//开启日志打印

/**
 * Created by zhouwei on 17/2/26.
 */
public class CustomDownloader implements Downloader {
    @Override
    public Response load(Uri uri, int networkPolicy) throws IOException {
        return null;
    }
    @Override
    public void shutdown() {
    }
}

        //配置下载器
        builder.downloader(new CustomDownloader());
        //构造一个Picasso
        Picasso picasso = builder.build();

        //配置缓存
        LruCache cache = new LruCache(5*1024*1024);// 设置缓存大小
        builder.memoryCache(cache);

        //配置线程池
        ExecutorService executorService = Executors.newFixedThreadPool(8);
        builder.executor(executorService);

 /**
   * Set the global instance returned from {@link #with}.
   * <p>
   * This method must be called before any calls to {@link #with} and may only be called once.
   */
  public static void setSingletonInstance(Picasso picasso) {
    synchronized (Picasso.class) {
      if (singleton != null) {
        throw new IllegalStateException("Singleton instance already exists.");
      }
      singleton = picasso;
    }
  }

 @Override
    public void onCreate() {
        super.onCreate();
        // 配置全局的Picasso instance 
        Picasso.Builder builder = new Picasso.Builder(this);
        //配置下载器
        builder.downloader(new CustomDownloader());
        //配置缓存
        LruCache cache = new LruCache(5*1024*1024);// 设置缓存大小
        builder.memoryCache(cache);
        //配置线程池
        ExecutorService executorService = Executors.newFixedThreadPool(8);
        builder.executor(executorService);
        //构造一个Picasso
        Picasso picasso = builder.build();
        // 设置全局单列instance 
        Picasso.setSingletonInstance(picasso);
    }

Picasso.with(this).load("http://ww3.sinaimg.cn/large/610dc034jw1fasakfvqe1j20u00mhgn2.jpg").into(mImageView);