Android 图片加载问题

最新推荐文章于 2025-08-07 17:35:28 发布

转载最新推荐文章于 2025-08-07 17:35:28 发布 · 570 阅读

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#android #图片 #缓存

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Picasso是一个专为Android平台设计的图片加载库，提供了灵活的图片处理功能，如调整大小、裁剪、转换为圆角等。通过自动重用视图和缓存机制，有效地减少了内存消耗，支持多种图片来源，并允许用户自定义转换以实现高级效果。

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1、Picasso (http://square.github.io/picasso/)

Picasso是一个用于Android平台上的下载和缓存图片的项目。它有许多定制选项，如何处理下载图片（包括调整和裁剪，以及提供一个接口让你随自己心意将图片转换成圆角等）。Picasso将要下载的图片（如果没有缓存）并将它负载到指定的目标，转换图片以适合所显示的ImageView，来减少内存消耗。

Adapter re-use is automatically detected and the previous download canceled.

@Override public void getView(int position, View convertView, ViewGroup parent) {
  SquaredImageView view = (SquaredImageView) convertView;
  if (view == null) {
    view = new SquaredImageView(context);
  }
  String url = getItem(position);

  Picasso.with(context).load(url).into(view);
}

Image Transformations

Transform images to better fit into layouts and to reduce memory size.

Picasso.with(context)
  .load(url)
  .resize(50, 50)
  .centerCrop()
  .into(imageView)

You can also specify custom transformations for more advanced effects.

public class CropSquareTransformation implements Transformation {
  @Override public Bitmap transform(Bitmap source) {
    int size = Math.min(source.getWidth(), source.getHeight());
    int x = (source.getWidth() - size) / 2;
    int y = (source.getHeight() - size) / 2;
    Bitmap result = Bitmap.createBitmap(source, x, y, size, size);
    if (result != source) {
      source.recycle();
    }
    return result;
  }

  @Override public String key() { return "square()"; }
}

Pass an instance of this class to the transform method.

Place Holders

Picasso supports both download and error placeholders as optional features.

Picasso.with(context)
    .load(url)
    .placeholder(R.drawable.user_placeholder)
    .error(R.drawable.user_placeholder_error)
    .into(imageView);

A request will be retried three times before the error placeholder is shown.

Resource Loading

Resources, assets, files, content providers are all supported as image sources.

Picasso.with(context).load(R.drawable.landing_screen).into(imageView1);
Picasso.with(context).load(new File(...)).into(imageView2);

<dependency> <groupId>com.squareup.picasso</groupId> <artifactId>picasso</artifactId> <version>2.2.0</version></dependency>