Android Glide设置默认图片、异常图片为圆形图片

亦凉 2022-06-07 00:35 312阅读 0赞

### **Android Glide4 异步图片框架** ###

*  [简介篇： Glide框架][Glide]
 *  [迁移篇：Glide V4 框架新特性（Migrating from v3 to v4）][Glide V4 _Migrating from v3 to v4]
 *  [基础篇：Android开发中使用Glide V4 中Generated API特性][Android_Glide V4 _Generated API]
 *  [进级篇：Kotlin编程开发之Glide V4使用OkHttp3作为传输层][Kotlin_Glide V4_OkHttp3]

--------------------

**前言**：

在项目开发中，是需要经常用到圆形图片的，设置默认图片，设置资源图片等等。

若是，异常图片，默认图片都需要美工妹子做成圆形图片，无疑增加了美工妹子的工作量。本着当活雷锋的思想，程序员能搞定的事情，绝不麻烦美工妹子。

要说图片异步加载框架，现今最流行的非Glide莫属，连谷歌I/O App都在使用，可见它的强大之处。

### **根据源码走向找到，设置默认图片，异常图片的方法**。 ###

众所周知，Glide的开启加载是通过调用`GlideApp.with().....into()或者preload()`.

--------------------

#### **1**. 首先,进入RequestBuilder类\#into()： ####

/** * Set the target the resource will be loaded into. * * @param target The target to load the resource into. * @return The given target. * @see RequestManager#clear(Target) */
      public <Y extends Target<TranscodeType>> Y into(@NonNull Y target) {
        Util.assertMainThread();
        Preconditions.checkNotNull(target);
        if (!isModelSet) {
          throw new IllegalArgumentException("You must call #load() before calling #into()");
        }
    
        Request previous = target.getRequest();
    
        if (previous != null) {
          requestManager.clear(target);
        }
    
        requestOptions.lock();
        Request request = buildRequest(target);
        target.setRequest(request);
        requestManager.track(target, request);
    
        return target;
      }

#### **2. 接下，源码来走向到RequestManager类中track()**: ####

void track(Target<?> target, Request request) {
        targetTracker.track(target);
        requestTracker.runRequest(request);
      }

#### **3. 在接下来，源码走向到RequestTracker类中runRequest()**: ####

/** * Starts tracking the given request. */
      public void runRequest(Request request) {
        requests.add(request);
        if (!isPaused) {
          request.begin();
        } else {
          pendingRequests.add(request);
        }
      }

#### **4. 最终走向到SingleRequest类中begin()**: ####

@Override
    public void begin() {
        stateVerifier.throwIfRecycled();
        startTime = LogTime.getLogTime();
        if (model == null) {
          if (Util.isValidDimensions(overrideWidth, overrideHeight)) {
            width = overrideWidth;
            height = overrideHeight;
          }
          // Only log at more verbose log levels if the user has set a fallback drawable, because
          // fallback Drawables indicate the user expects null models occasionally.
          int logLevel = getFallbackDrawable() == null ? Log.WARN : Log.DEBUG;
          onLoadFailed(new GlideException("Received null model"), logLevel);
          return;
        }
    
        status = Status.WAITING_FOR_SIZE;
        if (Util.isValidDimensions(overrideWidth, overrideHeight)) {
          onSizeReady(overrideWidth, overrideHeight);
        } else {
          target.getSize(this);
        }
    
        if ((status == Status.RUNNING || status == Status.WAITING_FOR_SIZE)
            && canNotifyStatusChanged()) {
          target.onLoadStarted(getPlaceholderDrawable());
        }
        if (Log.isLoggable(TAG, Log.VERBOSE)) {
          logV("finished run method in " + LogTime.getElapsedMillis(startTime));
        }
    }

可以从源码`target.onLoadStarted(getPlaceholderDrawable())`发觉，最后是通过Target对象的onLoadStarted()方法来设置默认空白图片的。

**SingleRequest类中设置异常图片的源码**：

private void setErrorPlaceholder() {
        if (!canNotifyStatusChanged()) {
          return;
        }
    
        Drawable error = null;
        if (model == null) {
          error = getFallbackDrawable();
        }
        // Either the model isn't null, or there was no fallback drawable set.
        if (error == null) {
          error = getErrorDrawable();
        }
        // The model isn't null, no fallback drawable was set or no error drawable was set.
        if (error == null) {
          error = getPlaceholderDrawable();
        }
        target.onLoadFailed(error);
      }

可以从源码`target.onLoadFailed(error)`可知，是通过Target对象的onLoadFailed()方法来设置异常图片的。

**长征路已经走完一半，已经找到了最后的源码走向。剩下来，只需要自定义一个Target子类。**

#### **Glide中已经存在一个ImageViewTarget类，查看源码如下**： ####

public abstract class ImageViewTarget<Z> extends ViewTarget<ImageView, Z>
        implements Transition.ViewAdapter {
    
      @Nullable
      private Animatable animatable;
    
      public ImageViewTarget(ImageView view) {
        super(view);
      }
    
      /** * Returns the current { @link android.graphics.drawable.Drawable} being displayed in the view * using { @link android.widget.ImageView#getDrawable()}. */
      @Override
      @Nullable
      public Drawable getCurrentDrawable() {
        return view.getDrawable();
      }
    
      /** * Sets the given { @link android.graphics.drawable.Drawable} on the view using { @link * android.widget.ImageView#setImageDrawable(android.graphics.drawable.Drawable)}. * * @param drawable { @inheritDoc} */
      @Override
      public void setDrawable(Drawable drawable) {
        view.setImageDrawable(drawable);
      }
    
      /** * Sets the given { @link android.graphics.drawable.Drawable} on the view using { @link * android.widget.ImageView#setImageDrawable(android.graphics.drawable.Drawable)}. * * @param placeholder { @inheritDoc} */
      @Override
      public void onLoadStarted(@Nullable Drawable placeholder) {
        super.onLoadStarted(placeholder);
        setResourceInternal(null);
        setDrawable(placeholder);
      }
    
      /** * Sets the given { @link android.graphics.drawable.Drawable} on the view using { @link * android.widget.ImageView#setImageDrawable(android.graphics.drawable.Drawable)}. * * @param errorDrawable { @inheritDoc} */
      @Override
      public void onLoadFailed(@Nullable Drawable errorDrawable) {
        super.onLoadFailed(errorDrawable);
        setResourceInternal(null);
        setDrawable(errorDrawable);
      }
    
      /** * Sets the given { @link android.graphics.drawable.Drawable} on the view using { @link * android.widget.ImageView#setImageDrawable(android.graphics.drawable.Drawable)}. * * @param placeholder { @inheritDoc} */
      @Override
      public void onLoadCleared(@Nullable Drawable placeholder) {
        super.onLoadCleared(placeholder);
        setResourceInternal(null);
        setDrawable(placeholder);
      }
    
      @Override
      public void onResourceReady(Z resource, @Nullable Transition<? super Z> transition) {
        if (transition == null || !transition.transition(resource, this)) {
          setResourceInternal(resource);
        } else {
          maybeUpdateAnimatable(resource);
        }
      }
    
      @Override
      public void onStart() {
        if (animatable != null) {
          animatable.start();
        }
      }
    
      @Override
      public void onStop() {
        if (animatable != null) {
          animatable.stop();
        }
      }
    
      private void setResourceInternal(@Nullable Z resource) {
        maybeUpdateAnimatable(resource);
        setResource(resource);
      }
    
      private void maybeUpdateAnimatable(@Nullable Z resource) {
        if (resource instanceof Animatable) {
          animatable = (Animatable) resource;
          animatable.start();
        } else {
          animatable = null;
        }
      }
    
      protected abstract void setResource(@Nullable Z resource);
    }

从源码可知，无论是空白图片，还是异常图片都是最后走向到`setDrawable(Drawable drawable)`。

源码寻找之路已经走完，马上就可以实现自己需要的需求，继续撸起。

### **定义一个默认，异常，资源图片都为圆形的 ImageViewTarget子类**。 ###

--------------------

**分析**：

*  定义ImageViewTarget子类：
 *  重写`setDrawable(Drawable drawable)`，异常，默认空白图片设置为圆形。
 *  实现抽象方法`setResource( Bitmap resource)`,正常加载的资源图片设置为圆形

**代码编写如下**：

/** * * 设置 默认图片，异常图片，指定路径的图片为圆角图片 */
    
    public class CircleBitmapTarget extends ImageViewTarget<Bitmap> { 
        public CircleBitmapTarget(ImageView view) {
            super(view);
        }
    
        /** * 从指定路径加载的Bitmap * @param resource */
        @Override
        protected void setResource(@Nullable Bitmap resource) {
             bindCircleBitmapToImageView(resource);
        }
        /** * * onLoadFailed()和onLoadStarted调用该方法，用于设置默认的图片和异常图片 * 设置默认图片 * @param drawable */
        @Override
        public void setDrawable(Drawable drawable) {
            if (drawable instanceof BitmapDrawable){
               Bitmap bitmap1= ((BitmapDrawable) drawable).getBitmap();
              bindCircleBitmapToImageView(bitmap1);
            }else{
                view.setImageDrawable(drawable);
            }
        }
    
        /** * 通过RoundedBitmapDrawable绘制圆形Bitmap,且加载ImageView. * @param bitmap */
        private void bindCircleBitmapToImageView(Bitmap bitmap){
            RoundedBitmapDrawable bitmapDrawable=  RoundedBitmapDrawableFactory.create(view.getContext().getResources(),bitmap);
            bitmapDrawable.setCircular(true);
            view.setImageDrawable(bitmapDrawable);
        }
    }

**最后使用方式**：

GlideRequest<Bitmap> glideRequest = GlideApp.with(context).asBitmap();
            glideRequest.load(imageUrl).error(errorResourceId)//异常时候显示的图片
                    .placeholder(placeResourceId)//加载成功前显示的图片
                    .fallback(nullResourceId)//url为空的时候，显示的图片
                    .into(new CircleBitmapTarget(imageView));//在RequestBuilder<Bitmap> 中使用自定义的ImageViewTarget

[Glide]: http://blog.csdn.net/hexingen/article/details/72577453
[Glide V4 _Migrating from v3 to v4]: http://blog.csdn.net/hexingen/article/details/72578066
[Android_Glide V4 _Generated API]: http://blog.csdn.net/hexingen/article/details/72579529
[Kotlin_Glide V4_OkHttp3]: http://blog.csdn.net/hexingen/article/details/76422241