【源码分析】View绘制流程

绘制的起始流程起于ViewRoot 的实现类 ViewRootImpl 里面的performTraversals()方法,在此方法中实现
onMeasure , onLayout , onDraw 等流程,流程图如下:
【源码分析】View绘制流程_第1张图片

一. MeasureSpec(测量规格)的获取流程:

  1. 顶级View–DecorView里面,在ViewRootImpl 类中的performTraversals()里面 —> 通过 measureHierarchy()法获取
 private boolean measureHierarchy(final View host, final WindowManager.LayoutParams lp,
            final Resources res, final int desiredWindowWidth, final int desiredWindowHeight) {
	 //省略相关代码
	 
	childWidthMeasureSpec = getRootMeasureSpec(desiredWindowWidth, lp.width);
	childHeightMeasureSpec = getRootMeasureSpec(desiredWindowHeight, lp.height);
	
	//省略相关代码
 }
.
.
.     进入getRootMeasureSpec方法 获取 measureSpec
.
.
    private static int getRootMeasureSpec(int windowSize, int rootDimension) {
        int measureSpec;
        switch (rootDimension) {

        case ViewGroup.LayoutParams.MATCH_PARENT:
            // MATCH_PARENT: 精确模式 大小就是窗口的大小,设置为:EXACTLY
            measureSpec = MeasureSpec.makeMeasureSpec(windowSize, MeasureSpec.EXACTLY);
            break;
        case ViewGroup.LayoutParams.WRAP_CONTENT:
            // WRAP_CONTENT: 最大模式,大小不能超过窗口大小,设置为:AT_MOST
            measureSpec = MeasureSpec.makeMeasureSpec(windowSize, MeasureSpec.AT_MOST);
            break;
        default:
            //固定数值: 精确模式,默认情况下设置为当前模式:EXACTLY
            measureSpec = MeasureSpec.makeMeasureSpec(rootDimension, MeasureSpec.EXACTLY);
            break;
        }
        return measureSpec; //获取到measureSpec
    }

  1. 布局View,measure过程通过ViewGrop传递获取,以LinearLayout为例,子View的measure
    在measureChildBeforeLayout()方法中 —> 调用measureChildWithMargins()方法,在子View measure之前会先调用getChildMeasureSpec()获取MeasureSpec
void measureChildBeforeLayout(View child, int childIndex,
        int widthMeasureSpec, int totalWidth, int heightMeasureSpec,
        int totalHeight) {
    measureChildWithMargins(child, widthMeasureSpec, totalWidth,
            heightMeasureSpec, totalHeight);
}

 ---> 进入ViewGrop的measureChildWithMargins()方法

 protected void measureChildWithMargins(View child,
            int parentWidthMeasureSpec, int widthUsed,
            int parentHeightMeasureSpec, int heightUsed) {
        final MarginLayoutParams lp = (MarginLayoutParams) child.getLayoutParams();
        final int childWidthMeasureSpec = getChildMeasureSpec(parentWidthMeasureSpec,
                mPaddingLeft + mPaddingRight + lp.leftMargin + lp.rightMargin
                        + widthUsed, lp.width);
        final int childHeightMeasureSpec = getChildMeasureSpec(parentHeightMeasureSpec,
                mPaddingTop + mPaddingBottom + lp.topMargin + lp.bottomMargin
                        + heightUsed, lp.height);
        child.measure(childWidthMeasureSpec, childHeightMeasureSpec);
    }


 ---> 调用getChildMeasureSpec()获取MeasureSpec

public static int getChildMeasureSpec(int spec, int padding, int childDimension) {
        int specMode = MeasureSpec.getMode(spec);
        int specSize = MeasureSpec.getSize(spec);

        int size = Math.max(0, specSize - padding);

        int resultSize = 0;
        int resultMode = 0;

        switch (specMode) {
        case MeasureSpec.EXACTLY:
            if (childDimension >= 0) {
                resultSize = childDimension;
                resultMode = MeasureSpec.EXACTLY;
            } else if (childDimension == LayoutParams.MATCH_PARENT) {
                resultSize = size;
                resultMode = MeasureSpec.EXACTLY;
            } else if (childDimension == LayoutParams.WRAP_CONTENT) {
                resultSize = size;
                resultMode = MeasureSpec.AT_MOST;
            }
            break;

        case MeasureSpec.AT_MOST:
            if (childDimension >= 0) {
                resultSize = childDimension;
                resultMode = MeasureSpec.EXACTLY;
            } else if (childDimension == LayoutParams.MATCH_PARENT) {
                resultSize = size;
                resultMode = MeasureSpec.AT_MOST;
            } else if (childDimension == LayoutParams.WRAP_CONTENT) {
                resultSize = size;
                resultMode = MeasureSpec.AT_MOST;
            }
            break;

        case MeasureSpec.UNSPECIFIED:
            if (childDimension >= 0) {
                resultSize = childDimension;
                resultMode = MeasureSpec.EXACTLY;
            } else if (childDimension == LayoutParams.MATCH_PARENT) {
                resultSize = View.sUseZeroUnspecifiedMeasureSpec ? 0 : size;
                resultMode = MeasureSpec.UNSPECIFIED;
            } else if (childDimension == LayoutParams.WRAP_CONTENT) {
                resultSize = View.sUseZeroUnspecifiedMeasureSpec ? 0 : size;
                resultMode = MeasureSpec.UNSPECIFIED;
            }
            break;
        }
        return MeasureSpec.makeMeasureSpec(resultSize, resultMode);
    }

二. View工作流程

  1. measure: 测量宽高–View只需测量本身,ViewGroup测量本身外还需要变量测量子元素
    (1)View的测量

View的measure()方法 —> 调用onMeasure()方法 —> getDefaultSize()方法,获取到specSize
specSize:就是View测量后的大小

/**
		measure方法,调用onMeasure()方法
**/
 public final void measure(int widthMeasureSpec, int heightMeasureSpec) {
        boolean optical = isLayoutModeOptical(this);
       //省略部分代码

        if (forceLayout || needsLayout) {
            mPrivateFlags &= ~PFLAG_MEASURED_DIMENSION_SET;

            resolveRtlPropertiesIfNeeded();

            int cacheIndex = forceLayout ? -1 : mMeasureCache.indexOfKey(key);
            if (cacheIndex < 0 || sIgnoreMeasureCache) {
                onMeasure(widthMeasureSpec, heightMeasureSpec); //执行onMeasure方法
                mPrivateFlags3 &= ~PFLAG3_MEASURE_NEEDED_BEFORE_LAYOUT;
            } else {
                long value = mMeasureCache.valueAt(cacheIndex);
                setMeasuredDimensionRaw((int) (value >> 32), (int) value);
                mPrivateFlags3 |= PFLAG3_MEASURE_NEEDED_BEFORE_LAYOUT;
            }

            if ((mPrivateFlags & PFLAG_MEASURED_DIMENSION_SET) != PFLAG_MEASURED_DIMENSION_SET) {
                throw new IllegalStateException("View with id " + getId() + ": "
                        + getClass().getName() + "#onMeasure() did not set the"
                        + " measured dimension by calling"
                        + " setMeasuredDimension()");
            }

            mPrivateFlags |= PFLAG_LAYOUT_REQUIRED;
        }

       //省略部分代码
    }


/**
	 ---> 	onMeasure方法
**/
   protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        setMeasuredDimension(getDefaultSize(getSuggestedMinimumWidth(), widthMeasureSpec),
                getDefaultSize(getSuggestedMinimumHeight(), heightMeasureSpec));
    }


/**
	 ---> 	getDefaultSize方法,返回结果就是MeasureSpec.getSize 获取到的specSize 
		specSize:就是View测量后的大小
**/
    public static int getDefaultSize(int size, int measureSpec) {
        int result = size;
        int specMode = MeasureSpec.getMode(measureSpec);
        int specSize = MeasureSpec.getSize(measureSpec);

        switch (specMode) {
        case MeasureSpec.UNSPECIFIED: //系统内部的测量过程,可不做考虑,返回getSuggestedMinimumWidth()获取的数值
            result = size;
            break;
        case MeasureSpec.AT_MOST: //主要这两种情况下的返回
        case MeasureSpec.EXACTLY:
            result = specSize;
            break;
        }
        return result;
    }

(2)ViewGroup测量
ViewGroup没有重写View的onMeasure()方法,提供一个measureChildren()方法,遍历所有子元素的measure()方法

measureChildren() --> measureChild() --> child.measure()

通过调用getChildMeasureSpec()获取MeasureSpec

protected void measureChildren(int widthMeasureSpec, int heightMeasureSpec) {
    final int size = mChildrenCount;
    final View[] children = mChildren;
    for (int i = 0; i < size; ++i) {
        final View child = children[i];
        if ((child.mViewFlags & VISIBILITY_MASK) != GONE) {
            measureChild(child, widthMeasureSpec, heightMeasureSpec); //遍历所有子元素的measure()方法
        }
    }
}

/**
*** ---> measureChild方法
**/
protected void measureChild(View child, int parentWidthMeasureSpec,
        int parentHeightMeasureSpec) {
    final LayoutParams lp = child.getLayoutParams();
// 调用getChildMeasureSpec()获取MeasureSpec
    final int childWidthMeasureSpec = getChildMeasureSpec(parentWidthMeasureSpec,
            mPaddingLeft + mPaddingRight, lp.width);
    final int childHeightMeasureSpec = getChildMeasureSpec(parentHeightMeasureSpec,
            mPaddingTop + mPaddingBottom, lp.height);

    child.measure(childWidthMeasureSpec, childHeightMeasureSpec); //子元素的measure()方法
}

以LinearLayout为例分析ViewGroup的measure过程

onMeasure()方法根据方向选择 --> measureVertical()或者 measureHorizontal()方法 – > 遍历所有子View 执行measureChildBeforeLayout()方法 --> 调用子元素的measure()方法,子元素开始进入measure过程

mTotalLength 保存高度,子元素测量完毕后,LinearLayout开始测量自身的大小


   @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        if (mOrientation == VERTICAL) {
            measureVertical(widthMeasureSpec, heightMeasureSpec);
        } else {
            measureHorizontal(widthMeasureSpec, heightMeasureSpec);
        }
    }

 void measureVertical(int widthMeasureSpec, int heightMeasureSpec) {
     

        final int widthMode = MeasureSpec.getMode(widthMeasureSpec);
        final int heightMode = MeasureSpec.getMode(heightMeasureSpec);
//省略部分代码
        for (int i = 0; i < count; ++i) {
            final View child = getVirtualChildAt(i);
        
			//省略部分代码
      
            final LayoutParams lp = (LayoutParams) child.getLayoutParams();
            totalWeight += lp.weight;
            final boolean useExcessSpace = lp.height == 0 && lp.weight > 0;
            if (heightMode == MeasureSpec.EXACTLY && useExcessSpace) {
                final int totalLength = mTotalLength;
                mTotalLength = Math.max(totalLength, totalLength + lp.topMargin + lp.bottomMargin);
                skippedMeasure = true;
            } else {
                if (useExcessSpace) {
                    lp.height = LayoutParams.WRAP_CONTENT;
                }
                final int usedHeight = totalWeight == 0 ? mTotalLength : 0;
                measureChildBeforeLayout(child, i, widthMeasureSpec, 0,
                        heightMeasureSpec, usedHeight);

                final int childHeight = child.getMeasuredHeight();
                if (useExcessSpace) {
                
                    lp.height = 0;
                    consumedExcessSpace += childHeight;
                }

                final int totalLength = mTotalLength;
                mTotalLength = Math.max(totalLength, totalLength + childHeight + lp.topMargin +
                       lp.bottomMargin + getNextLocationOffset(child));

                if (useLargestChild) {
                    largestChildHeight = Math.max(childHeight, largestChildHeight);
                }
            }

        
            if ((baselineChildIndex >= 0) && (baselineChildIndex == i + 1)) {
               mBaselineChildTop = mTotalLength;
            }
           
           	//省略部分代码
        // Add in our padding
        mTotalLength += mPaddingTop + mPaddingBottom;

        int heightSize = mTotalLength;

      
        if (!allFillParent && widthMode != MeasureSpec.EXACTLY) {
            maxWidth = alternativeMaxWidth;
        }

        maxWidth += mPaddingLeft + mPaddingRight;

        // Check against our minimum width
        maxWidth = Math.max(maxWidth, getSuggestedMinimumWidth());

        setMeasuredDimension(resolveSizeAndState(maxWidth, widthMeasureSpec, childState),
                heightSizeAndState); //测量完子元素后,开始测量自身的大小

        if (matchWidth) {
            forceUniformWidth(count, heightMeasureSpec);
        }
    }

/**
      ---->   resolveSizeAndState()方法
 **/
public static int resolveSizeAndState(int size, int measureSpec, int childMeasuredState) {
        final int specMode = MeasureSpec.getMode(measureSpec);
        final int specSize = MeasureSpec.getSize(measureSpec);
        final int result;
        switch (specMode) {
            case MeasureSpec.AT_MOST:
                if (specSize < size) {
                    result = specSize | MEASURED_STATE_TOO_SMALL;
                } else {
                    result = size;
                }
                break;
            case MeasureSpec.EXACTLY:
                result = specSize;
                break;
            case MeasureSpec.UNSPECIFIED:
            default:
                result = size;
        }
        return result | (childMeasuredState & MEASURED_STATE_MASK);
    }
  1. layout: 确定宽高,及四个顶点位置

layout()方法确定View本身的位置,onLayout()方法确定所有子元素的位置

layout() —> setFrame() 设定四个顶点的位置 —> onLayout() 父容器确定子容器的位置(view 和viewGroup里面没有具体实现onLayout()方法) --> 进入layoutVertical()或者layoutHorizontal()法(以LinearLayout为例)–> 遍历所有子元素,通过setChildFrame()方法来指定对应的位置 --> 调用子元素的 layout()方法来完成位置确定

/**
        viewGroup ---> layout方法 
**/
  @Override
  public final void layout(int l, int t, int r, int b) {
      if (!mSuppressLayout && (mTransition == null || !mTransition.isChangingLayout())) {
          if (mTransition != null) {
              mTransition.layoutChange(this);
          }
          super.layout(l, t, r, b); // 执行view ---> layout方法
      } else {
          // record the fact that we noop'd it; request layout when transition finishes
          mLayoutCalledWhileSuppressed = true;
      }
  }

/**
        view ---> layout方法
**/
public void layout(int l, int t, int r, int b) {
        if ((mPrivateFlags3 & PFLAG3_MEASURE_NEEDED_BEFORE_LAYOUT) != 0) {
            onMeasure(mOldWidthMeasureSpec, mOldHeightMeasureSpec);
            mPrivateFlags3 &= ~PFLAG3_MEASURE_NEEDED_BEFORE_LAYOUT;
        }

        int oldL = mLeft;
        int oldT = mTop;
        int oldB = mBottom;
        int oldR = mRight;

        boolean changed = isLayoutModeOptical(mParent) ?
                setOpticalFrame(l, t, r, b) : setFrame(l, t, r, b);

        if (changed || (mPrivateFlags & PFLAG_LAYOUT_REQUIRED) == PFLAG_LAYOUT_REQUIRED) {
            onLayout(changed, l, t, r, b);   //执行onLayout()方法

            if (shouldDrawRoundScrollbar()) {
                if(mRoundScrollbarRenderer == null) {
                    mRoundScrollbarRenderer = new RoundScrollbarRenderer(this);
                }
            } else {
                mRoundScrollbarRenderer = null;
            }

            mPrivateFlags &= ~PFLAG_LAYOUT_REQUIRED;

            ListenerInfo li = mListenerInfo;
            if (li != null && li.mOnLayoutChangeListeners != null) {
                ArrayList listenersCopy =
                        (ArrayList)li.mOnLayoutChangeListeners.clone();
                int numListeners = listenersCopy.size();
                for (int i = 0; i < numListeners; ++i) {
                    listenersCopy.get(i).onLayoutChange(this, l, t, r, b, oldL, oldT, oldR, oldB);
                }
            }
        }

        final boolean wasLayoutValid = isLayoutValid();

        mPrivateFlags &= ~PFLAG_FORCE_LAYOUT;
        mPrivateFlags3 |= PFLAG3_IS_LAID_OUT;

        if (!wasLayoutValid && isFocused()) {
            mPrivateFlags &= ~PFLAG_WANTS_FOCUS;
            if (canTakeFocus()) {
                clearParentsWantFocus();
            } else if (getViewRootImpl() == null || !getViewRootImpl().isInLayout()) {
                clearFocusInternal(null, /* propagate */ true, /* refocus */ false);
                clearParentsWantFocus();
            } else if (!hasParentWantsFocus()) {
            }
        } else if ((mPrivateFlags & PFLAG_WANTS_FOCUS) != 0) {
            mPrivateFlags &= ~PFLAG_WANTS_FOCUS;
            View focused = findFocus();
            if (focused != null) {
                if (!restoreDefaultFocus() && !hasParentWantsFocus()) {
                    focused.clearFocusInternal(null, /* propagate */ true, /* refocus */ false);
                }
            }
        }

        if ((mPrivateFlags3 & PFLAG3_NOTIFY_AUTOFILL_ENTER_ON_LAYOUT) != 0) {
            mPrivateFlags3 &= ~PFLAG3_NOTIFY_AUTOFILL_ENTER_ON_LAYOUT;
            notifyEnterOrExitForAutoFillIfNeeded(true);
        }
    }

/**
        view 和viewGroup里面都没有具体实现onLayout()方法,以LinearLayout为例
**/
    @Override
    protected void onLayout(boolean changed, int l, int t, int r, int b) {
        if (mOrientation == VERTICAL) {
            layoutVertical(l, t, r, b);
        } else {
            layoutHorizontal(l, t, r, b);
        }
    }

/**
        进入layoutVertical()方法,以LinearLayout为例
**/
 void layoutVertical(int left, int top, int right, int bottom) {
        final int paddingLeft = mPaddingLeft;

        int childTop;
        int childLeft;

     // 主要代码
        for (int i = 0; i < count; i++) {
            final View child = getVirtualChildAt(i);
            if (child == null) {
                childTop += measureNullChild(i);
            } else if (child.getVisibility() != GONE) {
                final int childWidth = child.getMeasuredWidth();
                final int childHeight = child.getMeasuredHeight();
                final LinearLayout.LayoutParams lp =
                        (LinearLayout.LayoutParams) child.getLayoutParams();
                int gravity = lp.gravity;
                if (gravity < 0) {
                    gravity = minorGravity;
                }
                final int layoutDirection = getLayoutDirection();
                final int absoluteGravity = Gravity.getAbsoluteGravity(gravity, layoutDirection);
                switch (absoluteGravity & Gravity.HORIZONTAL_GRAVITY_MASK) {
                    case Gravity.CENTER_HORIZONTAL:
                        childLeft = paddingLeft + ((childSpace - childWidth) / 2)
                                + lp.leftMargin - lp.rightMargin;
                        break;

                    case Gravity.RIGHT:
                        childLeft = childRight - childWidth - lp.rightMargin;
                        break;

                    case Gravity.LEFT:
                    default:
                        childLeft = paddingLeft + lp.leftMargin;
                        break;
                }

                if (hasDividerBeforeChildAt(i)) {
                    childTop += mDividerHeight;
                }

                childTop += lp.topMargin; //childTop 增大,后面的子元素,靠下放置
                setChildFrame(child, childLeft, childTop + getLocationOffset(child),
                        childWidth, childHeight); //遍历所有子元素,通过setChildFrame()方法来指定对应的位置
                childTop += childHeight + lp.bottomMargin + getNextLocationOffset(child);

                i += getChildrenSkipCount(child, i);
            }
        }
    }

/**
       setChildFrame()方法,调用子元素的layout方法
**/
    private void setChildFrame(View child, int left, int top, int width, int height) {
        child.layout(left, top, left + width, top + height);
    }

  1. draw: 将View绘制到屏幕上

view中的draw()方法 --> 绘制背景 drawBackground(canvas) --> 绘制自己 onDraw(canvas) --> 绘制children dispatchDraw(canvas) --> 绘制装饰 (foreground, scrollbars) onDrawForeground(canvas)

 public void draw(Canvas canvas) {
        final int privateFlags = mPrivateFlags;
        final boolean dirtyOpaque = (privateFlags & PFLAG_DIRTY_MASK) == PFLAG_DIRTY_OPAQUE &&
                (mAttachInfo == null || !mAttachInfo.mIgnoreDirtyState);
        mPrivateFlags = (privateFlags & ~PFLAG_DIRTY_MASK) | PFLAG_DRAWN;

        /*
         * Draw traversal performs several drawing steps which must be executed
         * in the appropriate order:
         *
         *      1. Draw the background
         *      2. If necessary, save the canvas' layers to prepare for fading
         *      3. Draw view's content
         *      4. Draw children
         *      5. If necessary, draw the fading edges and restore layers
         *      6. Draw decorations (scrollbars for instance)
         */

        // Step 1, draw the background, if needed
        int saveCount;

        if (!dirtyOpaque) {
            drawBackground(canvas);
        }

        // skip step 2 & 5 if possible (common case)
        final int viewFlags = mViewFlags;
        boolean horizontalEdges = (viewFlags & FADING_EDGE_HORIZONTAL) != 0;
        boolean verticalEdges = (viewFlags & FADING_EDGE_VERTICAL) != 0;
        if (!verticalEdges && !horizontalEdges) {
            // Step 3, draw the content
            if (!dirtyOpaque) onDraw(canvas);

            // Step 4, draw the children
            dispatchDraw(canvas);

            drawAutofilledHighlight(canvas);

            // Overlay is part of the content and draws beneath Foreground
            if (mOverlay != null && !mOverlay.isEmpty()) {
                mOverlay.getOverlayView().dispatchDraw(canvas);
            }

            // Step 6, draw decorations (foreground, scrollbars)
            onDrawForeground(canvas);

            // Step 7, draw the default focus highlight
            drawDefaultFocusHighlight(canvas);

            if (debugDraw()) {
                debugDrawFocus(canvas);
            }

            // we're done...
            return;
        }

  

        boolean drawTop = false;
        boolean drawBottom = false;
        boolean drawLeft = false;
        boolean drawRight = false;

        float topFadeStrength = 0.0f;
        float bottomFadeStrength = 0.0f;
        float leftFadeStrength = 0.0f;
        float rightFadeStrength = 0.0f;

        // Step 2, save the canvas' layers
        int paddingLeft = mPaddingLeft;

        final boolean offsetRequired = isPaddingOffsetRequired();
        if (offsetRequired) {
            paddingLeft += getLeftPaddingOffset();
        }

        int left = mScrollX + paddingLeft;
        int right = left + mRight - mLeft - mPaddingRight - paddingLeft;
        int top = mScrollY + getFadeTop(offsetRequired);
        int bottom = top + getFadeHeight(offsetRequired);

        if (offsetRequired) {
            right += getRightPaddingOffset();
            bottom += getBottomPaddingOffset();
        }

        final ScrollabilityCache scrollabilityCache = mScrollCache;
        final float fadeHeight = scrollabilityCache.fadingEdgeLength;
        int length = (int) fadeHeight;

        // clip the fade length if top and bottom fades overlap
        // overlapping fades produce odd-looking artifacts
        if (verticalEdges && (top + length > bottom - length)) {
            length = (bottom - top) / 2;
        }

        // also clip horizontal fades if necessary
        if (horizontalEdges && (left + length > right - length)) {
            length = (right - left) / 2;
        }

        if (verticalEdges) {
            topFadeStrength = Math.max(0.0f, Math.min(1.0f, getTopFadingEdgeStrength()));
            drawTop = topFadeStrength * fadeHeight > 1.0f;
            bottomFadeStrength = Math.max(0.0f, Math.min(1.0f, getBottomFadingEdgeStrength()));
            drawBottom = bottomFadeStrength * fadeHeight > 1.0f;
        }

        if (horizontalEdges) {
            leftFadeStrength = Math.max(0.0f, Math.min(1.0f, getLeftFadingEdgeStrength()));
            drawLeft = leftFadeStrength * fadeHeight > 1.0f;
            rightFadeStrength = Math.max(0.0f, Math.min(1.0f, getRightFadingEdgeStrength()));
            drawRight = rightFadeStrength * fadeHeight > 1.0f;
        }

        saveCount = canvas.getSaveCount();

        int solidColor = getSolidColor();
        if (solidColor == 0) {
            if (drawTop) {
                canvas.saveUnclippedLayer(left, top, right, top + length);
            }

            if (drawBottom) {
                canvas.saveUnclippedLayer(left, bottom - length, right, bottom);
            }

            if (drawLeft) {
                canvas.saveUnclippedLayer(left, top, left + length, bottom);
            }

            if (drawRight) {
                canvas.saveUnclippedLayer(right - length, top, right, bottom);
            }
        } else {
            scrollabilityCache.setFadeColor(solidColor);
        }

        // Step 3, draw the content
        if (!dirtyOpaque) onDraw(canvas);

        // Step 4, draw the children
        dispatchDraw(canvas);

        // Step 5, draw the fade effect and restore layers
        final Paint p = scrollabilityCache.paint;
        final Matrix matrix = scrollabilityCache.matrix;
        final Shader fade = scrollabilityCache.shader;

        if (drawTop) {
            matrix.setScale(1, fadeHeight * topFadeStrength);
            matrix.postTranslate(left, top);
            fade.setLocalMatrix(matrix);
            p.setShader(fade);
            canvas.drawRect(left, top, right, top + length, p);
        }

        if (drawBottom) {
            matrix.setScale(1, fadeHeight * bottomFadeStrength);
            matrix.postRotate(180);
            matrix.postTranslate(left, bottom);
            fade.setLocalMatrix(matrix);
            p.setShader(fade);
            canvas.drawRect(left, bottom - length, right, bottom, p);
        }

        if (drawLeft) {
            matrix.setScale(1, fadeHeight * leftFadeStrength);
            matrix.postRotate(-90);
            matrix.postTranslate(left, top);
            fade.setLocalMatrix(matrix);
            p.setShader(fade);
            canvas.drawRect(left, top, left + length, bottom, p);
        }

        if (drawRight) {
            matrix.setScale(1, fadeHeight * rightFadeStrength);
            matrix.postRotate(90);
            matrix.postTranslate(right, top);
            fade.setLocalMatrix(matrix);
            p.setShader(fade);
            canvas.drawRect(right - length, top, right, bottom, p);
        }

        canvas.restoreToCount(saveCount);

        drawAutofilledHighlight(canvas);

        // Overlay is part of the content and draws beneath Foreground
        if (mOverlay != null && !mOverlay.isEmpty()) {
            mOverlay.getOverlayView().dispatchDraw(canvas);
        }

        // Step 6, draw decorations (foreground, scrollbars)
        onDrawForeground(canvas);

        if (debugDraw()) {
            debugDrawFocus(canvas);
        }
    }

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