Target相關(guān)

Target相關(guān)

通常我們是調(diào)用requestBuilder#into(ImageView)憾股，接下來(lái)看看环葵，ImageView是如果轉(zhuǎn)化為Target的咕缎。

// RequestBuilder.java
public ViewTarget<ImageView, TranscodeType> into(@NonNull ImageView view) {
    // ... 省略scaleType相關(guān)代碼

    // 可以看到是通過(guò)GlideContext構(gòu)建一個(gè)ViewTarget郭蕉，內(nèi)部是使用imageViewTargetFactory來(lái)構(gòu)建的
    return into(
        glideContext.buildImageViewTarget(view, transcodeClass),
        /*targetListener=*/ null,
        requestOptions,
        Executors.mainThreadExecutor());
}

// GlideContext.java

// 通過(guò)下方代碼分析劝赔，可以知道是在Glide的構(gòu)造函數(shù)中傳進(jìn)來(lái)的
private final ImageViewTargetFactory imageViewTargetFactory;

public GlideContext(
      ...
      @NonNull ImageViewTargetFactory imageViewTargetFactory,
      ...) {
    super(context.getApplicationContext());
    ...
    this.imageViewTargetFactory = imageViewTargetFactory;
    ...
}


public <X> ViewTarget<ImageView, X> buildImageViewTarget(ImageView imageView, Class<X> transcodeClass) {
    return imageViewTargetFactory.buildTarget(imageView, transcodeClass);
}

// Glide.java
Glide(...){

    ImageViewTargetFactory imageViewTargetFactory = new ImageViewTargetFactory();
    glideContext = new GlideContext(
            ...
            imageViewTargetFactory,
            ...);
}
    

// ImageViewTargetFactory.java
public class ImageViewTargetFactory {
  
  // 通過(guò)判斷不同的類型烘豹，實(shí)例化不同的ViewTarget
  public <Z> ViewTarget<ImageView, Z> buildTarget(
      @NonNull ImageView view, @NonNull Class<Z> clazz) {
    if (Bitmap.class.equals(clazz)) {
      return (ViewTarget<ImageView, Z>) new BitmapImageViewTarget(view);
    } else if (Drawable.class.isAssignableFrom(clazz)) {
      return (ViewTarget<ImageView, Z>) new DrawableImageViewTarget(view);
    } else {
      throw new IllegalArgumentException(
          "Unhandled class: " + clazz + ", try .as*(Class).transcode(ResourceTranscoder)");
    }
  }
}

通常我們是通過(guò)一個(gè)url去加載圖片的瓜贾，由上面RequestManger#load(string)代碼可以知道，RequestBuilder的transcodeClass是Drawable.class携悯，所以最后得到的target是DrawableImageViewTarget祭芦。

從Glide源碼分析二——Request相關(guān)中的SingleRequest#begin()可知，如果沒(méi)有設(shè)置overrideWidth/overrideHeight憔鬼，會(huì)通過(guò)viewTarget#getSize(SizeReadyCallback)獲取大小龟劲，獲取大小后在回調(diào)SizeReadyCallback#onSizeReady()通知SingleRequest加載圖片。

public abstract class ViewTarget<T extends View, Z> extends BaseTarget<Z> {
        
    protected final T view;
    private final SizeDeterminer sizeDeterminer;
    
    public ViewTarget(@NonNull T view) {
        this.view = Preconditions.checkNotNull(view);
        sizeDeterminer = new SizeDeterminer(view);
    }
  
    public void getSize(@NonNull SizeReadyCallback cb) {
        sizeDeterminer.getSize(cb);
    }  
    
    
    static final class SizeDeterminer {
    
        private final View view;
        private final List<SizeReadyCallback> cbs = new ArrayList<>();
        private SizeDeterminerLayoutListener layoutListener;
        
        SizeDeterminer(@NonNull View view) {
            this.view = view;
        }
        
        void getSize(@NonNull SizeReadyCallback cb) {
          int currentWidth = getTargetWidth();
          int currentHeight = getTargetHeight();
          // 如果view已經(jīng)可以獲取大小了逊彭，則回調(diào)SizeReadyCallback#onSizeReady(w,h)通知加載圖片
          if (isViewStateAndSizeValid(currentWidth, currentHeight)) {
            cb.onSizeReady(currentWidth, currentHeight);
            return;
          }

          if (!cbs.contains(cb)) {
            cbs.add(cb);
          }
          if (layoutListener == null) {
            
            // 通過(guò)添加PreDrawListener來(lái)獲取大小咸灿，獲取大小后會(huì)回調(diào)SizeReadyCallback#onSizeReady(w,h)通知加載圖片
            ViewTreeObserver observer = view.getViewTreeObserver();
            layoutListener = new SizeDeterminerLayoutListener(this);
            observer.addOnPreDrawListener(layoutListener);
          }
        }
        
        // 獲取view的高度
        private int getTargetHeight() {
          int verticalPadding = view.getPaddingTop() + view.getPaddingBottom();
          LayoutParams layoutParams = view.getLayoutParams();
          int layoutParamSize = layoutParams != null ? layoutParams.height : PENDING_SIZE;
          return getTargetDimen(view.getHeight(), layoutParamSize, verticalPadding);
        }
        
        private int getTargetDimen(int viewSize, int paramSize, int paddingSize) {
          
          int adjustedParamSize = paramSize - paddingSize;
          
          // layoutParam中的Size可用就用paramSize
          if (adjustedParamSize > 0) {
            return adjustedParamSize;
          }
          
          // 如果view申請(qǐng)了繪制（例如調(diào)用了requestLayout），則返回0（無(wú)效尺寸侮叮，后面會(huì)去測(cè)量）
          if (waitForLayout && view.isLayoutRequested()) {
            return PENDING_SIZE;
          }

          // 如果view已經(jīng)有了寬高避矢，則返回view的寬高
          int adjustedViewSize = viewSize - paddingSize;
          if (adjustedViewSize > 0) {
            return adjustedViewSize;
          }

          // 如果view沒(méi)有申請(qǐng)繪制，且尺寸是wrap_content，則返回屏幕寬高的最大值
          if (!view.isLayoutRequested() && paramSize == LayoutParams.WRAP_CONTENT) {
            
            return getMaxDisplayLength(view.getContext());
          }

          // 不滿足上述條件則返回?zé)o效尺寸
          return PENDING_SIZE;
        }
        
        
        void checkCurrentDimens() {
          if (cbs.isEmpty()) {
            return;
          }

          int currentWidth = getTargetWidth();
          int currentHeight = getTargetHeight();
          if (!isViewStateAndSizeValid(currentWidth, currentHeight)) {
            return;
          }

          // 獲取到view的大小后审胸，通過(guò)SizeReadyCallback#onSizeReady(w,h)通知加載圖片
          notifyCbs(currentWidth, currentHeight);
          
          // 回調(diào)完后清除之前創(chuàng)建的PreDrawListener和添加的SizeReadyCallback
          clearCallbacksAndListener();
        }
        
        
        private static final class SizeDeterminerLayoutListener
        implements ViewTreeObserver.OnPreDrawListener {
          private final WeakReference<SizeDeterminer> sizeDeterminerRef;

          SizeDeterminerLayoutListener(@NonNull SizeDeterminer sizeDeterminer) {
            sizeDeterminerRef = new WeakReference<>(sizeDeterminer);
          }

          @Override
          public boolean onPreDraw() {
            // 這時(shí)可以正常獲取到大小了亥宿，通過(guò)SizeDeterminer去獲取大小
            SizeDeterminer sizeDeterminer = sizeDeterminerRef.get();
            if (sizeDeterminer != null) {
              sizeDeterminer.checkCurrentDimens();
            }
            return true;
          }
        }
        
    }

}

ViewTarget通過(guò)SizeDeterminer獲取大小，當(dāng)view已經(jīng)有大小或可以通過(guò)LayoutPrams獲取大小時(shí)砂沛，直接回調(diào)烫扼；否則通過(guò)添加PreDrawListener來(lái)獲取大小，之后再回調(diào)碍庵。

public abstract class ImageViewTarget<Z> extends ViewTarget<ImageView, Z>
    implements Transition.ViewAdapter {
    
  // 其他onLoadXxx(...)都差不多
  @Override
  public void onLoadStarted(@Nullable Drawable placeholder) {
    super.onLoadStarted(placeholder);
    setResourceInternal(null);
    setDrawable(placeholder);
  }
  
  // 當(dāng)資源獲取成功時(shí)會(huì)回調(diào)此方法
  @Override
  public void onResourceReady(@NonNull Z resource, @Nullable Transition<? super Z> transition) {
    if (transition == null || !transition.transition(resource, this)) {
      setResourceInternal(resource);
    } else {
      maybeUpdateAnimatable(resource);
    }
  }
  
  private void setResourceInternal(@Nullable Z resource) {
    // 通知子類加載資源映企，例如DrawableImageViewTarget就是直接調(diào)用ImageView#setImageDrawable(resource)
    setResource(resource);
    // 如果資源是動(dòng)畫的話，則開(kāi)啟動(dòng)畫
    maybeUpdateAnimatable(resource);
  }
  
  @Override
  public void setDrawable(Drawable drawable) {
    view.setImageDrawable(drawable);
  }
  
  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);
    
}