Fresco加载图片

1.项目引用Fresco库

在app目录下的build.gradle添加

dependencies {
    ...
    //要添加的
    implementation 'com.facebook.fresco:fresco:1.10.0'
}

如果是加载网络图片，需要获取网络请求权限
在AndroidManifest.xml中的manifest标签下添加

<uses-permission android:name="android.permission.INTERNET"/>

如果还要使用图片的本地缓存等，也需要申请对应的权限。

2.加载图片

2.1 简单使用SimpleDraweeView加载图片

在布局中加入SimpleDraweeView控件

<com.facebook.drawee.view.SimpleDraweeView
        android:id="@+id/simple_drawee_view"
        android:layout_width="200dp"
        android:layout_height="200dp" />

在Java代码中开始加载图片

SimpleDraweeView mSimpleView = findViewById(R.id.simple_drawee_view);
mSimpleView.setImageURI(Uri.parse("http://ww4.sinaimg.cn/large/90bd89ffjw1eqvmd6o8r6j20go0p5ju2.jpg"));

这样可以了。当然SimpleDraweeView还有很多属性可以用。
Fresco官方详细介绍：https://www.fresco-cn.org/docs/using-drawees-xml.html

2.2 显示图片加载进度条

想要显示进度条只需要给SimpleDraweeView设置一个Hierarchy

GenericDraweeHierarchy hierarchy = GenericDraweeHierarchyBuilder
                .newInstance(getResources())
                .setProgressBarImage(new ProgressBarDrawable()).build();
mSimpleView.setHierarchy(hierarchy);

ProgressBarDrawable是Fresco提供的一个默认的进度条，我们也可以自定义进度条,继承Drawable并实现自己想要的效果

class CustomProgressBar extends Drawable {
   @Override
   protected boolean onLevelChange(int level) {
     // level is on a scale of 0-10,000
     // where 10,000 means fully downloaded

     // your app's logic to change the drawable's
     // appearance here based on progress
   }
}

Fresco官方介绍：https://www.fresco-cn.org/docs/progress-bars.html

2.2 对显示的图片做出更多的控制

可以使用DraweeController，继承BaseControllerListener并选择实现自己需要的方法，在回调方法中实现自己的逻辑

DraweeController controller = Fresco.newDraweeControllerBuilder()
                .setUri(Uri.parse("http://ww4.sinaimg.cn/large/90bd89ffjw1eqvmd6o8r6j20go0p5ju2.jpg"))
                .setOldController(mSimpleView.getController())
                .setControllerListener(new ControllerListener())
                .build();

mSimpleView.setController(controller);

private class ControllerListener extends BaseControllerListener<ImageInfo> {
        public ControllerListener() {
            super();
        }

        @Override
        public void onFinalImageSet(String id, @Nullable ImageInfo imageInfo, @Nullable Animatable animatable) {
            super.onFinalImageSet(id, imageInfo, animatable);
        }

        @Override
        public void onIntermediateImageSet(String id, @Nullable ImageInfo imageInfo) {
            super.onIntermediateImageSet(id, imageInfo);
        }

        @Override
        public void onFailure(String id, Throwable throwable) {
            super.onFailure(id, throwable);
        }
    }

由于我也是初学Fresco，就不胡乱介绍了。更加详细的介绍请参考Fresco官方介绍：https://www.fresco-cn.org/docs/using-controllerbuilder.html

2.3 对图片的请求过程做处理

使用ImageRequest时可以设置监听事件，能够监听图片的所有请求过程，然后将ImageRequest使用DraweeController来加载图片

ImageRequest request = ImageRequestBuilder
                .newBuilderWithSource(Uri.parse("http://ww4.sinaimg.cn/large/90bd89ffjw1eqvmd6o8r6j20go0p5ju2.jpg"))
                .setResizeOptions(new ResizeOptions(500, 500))
                .setRequestListener(mRequestListener)
                .build();

DraweeController controller = Fresco.newDraweeControllerBuilder()
                .setImageRequest(request)
                .setOldController(mSimpleView.getController())
                .setControllerListener(new ControllerListener())
                .build();

mSimpleView.setController(controller);

private RequestListener mRequestListener = new RequestListener() {
        @Override
        public void onRequestStart(ImageRequest request, Object callerContext, String requestId, boolean isPrefetch) {

        }

        @Override
        public void onRequestSuccess(ImageRequest request, String requestId, boolean isPrefetch) {

        }

        @Override
        public void onRequestFailure(ImageRequest request, String requestId, Throwable throwable, boolean isPrefetch) {

        }

        @Override
        public void onRequestCancellation(String requestId) {

        }

        @Override
        public void onProducerStart(String requestId, String producerName) {

        }

        @Override
        public void onProducerEvent(String requestId, String producerName, String eventName) {

        }

        @Override
        public void onProducerFinishWithSuccess(String requestId, String producerName, Map<String, String> extraMap) {

        }

        @Override
        public void onProducerFinishWithFailure(String requestId, String producerName, Throwable t, Map<String, String> extraMap) {

        }

        @Override
        public void onProducerFinishWithCancellation(String requestId, String producerName, Map<String, String> extraMap) {

        }

        @Override
        public void onUltimateProducerReached(String requestId, String producerName, boolean successful) {

        }

        @Override
        public boolean requiresExtraMap(String requestId) {
            return false;
        }
    };

.setResizeOptions(new ResizeOptions(500, 500))是设置加载图片的大小的。Fresco官方介绍地址：
https://www.fresco-cn.org/docs/image-requests.html
http://frescolib.org/docs/listening-to-events.html#motivation

3.总结

我只是写出了学习Fresco的一些笔记，Fresco功能很强大，比如还有自定义View，多图片处理，图片裁剪等等，想要学习请到Fresco官方网站学习，我的个人笔记仅供自己记录。
Fresco官方网站：https://www.fresco-cn.org/