Android View measure（三）常用方法

 

ViewGroup.measureChildren()
ViewGroup.measureChild()
ViewGroup.measureChildWithMargins()

 

 

 

    /**
     * Ask one of the children of this view to measure itself, taking into
     * account both the MeasureSpec requirements for this view and its padding
     * and margins. The child must have MarginLayoutParams The heavy lifting is
     * done in getChildMeasureSpec.
     *
     * @param child The child to measure
     * @param parentWidthMeasureSpec The width requirements for this view
     * @param widthUsed Extra space that has been used up by the parent
     *        horizontally (possibly by other children of the parent)
     * @param parentHeightMeasureSpec The height requirements for this view
     * @param heightUsed Extra space that has been used up by the parent
     *        vertically (possibly by other children of the parent)
     */
    protected void measureChildWithMargins(View child,
            int parentWidthMeasureSpec, int widthUsed,
            int parentHeightMeasureSpec, int heightUsed) {
		// 1 類型轉換
        final MarginLayoutParams lp = (MarginLayoutParams) child.getLayoutParams();


		// 2 getChildMeasureSpec方法
        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);
    }
	

 

此方法針對第一個參數傳遞的子視圖進行Measure操作。
1. 傳遞的子視圖LayoutParams必須是或者繼承自MarginLayoutParams，否者會拋出轉換異常

    /**
     * Does the hard part of measureChildren: figuring out the MeasureSpec to
     * pass to a particular child. This method figures out the right MeasureSpec
     * for one dimension (height or width) of one child view.
     *
     * The goal is to combine information from our MeasureSpec with the
     * LayoutParams of the child to get the best possible results. For example,
     * if the this view knows its size (because its MeasureSpec has a mode of
     * EXACTLY), and the child has indicated in its LayoutParams that it wants
     * to be the same size as the parent, the parent should ask the child to
     * layout given an exact size.
     *
     * @param spec The requirements for this view
     * @param padding The padding of this view for the current dimension and
     *        margins, if applicable
     * @param childDimension How big the child wants to be in the current
     *        dimension
     * @return a MeasureSpec integer for the child
     */
    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) {
        // Parent has imposed an exact size on us
        case MeasureSpec.EXACTLY:
            if (childDimension >= 0) {
                resultSize = childDimension;
                resultMode = MeasureSpec.EXACTLY;
            } else if (childDimension == LayoutParams.FILL_PARENT) {
                // Child wants to be our size. So be it.
                resultSize = size;
                resultMode = MeasureSpec.EXACTLY;
            } else if (childDimension == LayoutParams.WRAP_CONTENT) {
                // Child wants to determine its own size. It can't be
                // bigger than us.
                resultSize = size;
                resultMode = MeasureSpec.AT_MOST;
            }
            break;


        // Parent has imposed a maximum size on us
        case MeasureSpec.AT_MOST:
            if (childDimension >= 0) {
                // Child wants a specific size... so be it
                resultSize = childDimension;
                resultMode = MeasureSpec.EXACTLY;
            } else if (childDimension == LayoutParams.FILL_PARENT) {
                // Child wants to be our size, but our size is not fixed.
                // Constrain child to not be bigger than us.
                resultSize = size;
                resultMode = MeasureSpec.AT_MOST;
            } else if (childDimension == LayoutParams.WRAP_CONTENT) {
                // Child wants to determine its own size. It can't be
                // bigger than us.
                resultSize = size;
                resultMode = MeasureSpec.AT_MOST;
            }
            break;


        // Parent asked to see how big we want to be
        case MeasureSpec.UNSPECIFIED:
            if (childDimension >= 0) {
                // Child wants a specific size... let him have it
                resultSize = childDimension;
                resultMode = MeasureSpec.EXACTLY;
            } else if (childDimension == LayoutParams.FILL_PARENT) {
                // Child wants to be our size... find out how big it should
                // be
                resultSize = 0;
                resultMode = MeasureSpec.UNSPECIFIED;
            } else if (childDimension == LayoutParams.WRAP_CONTENT) {
                // Child wants to determine its own size.... find out how
                // big it should be
                resultSize = 0;
                resultMode = MeasureSpec.UNSPECIFIED;
            }
            break;
        }
        return MeasureSpec.makeMeasureSpec(resultSize, resultMode);
    }	

 

 

 

    protected void measureChildWithMargins(View child,
            int parentWidthMeasureSpec, int widthUsed,
            int parentHeightMeasureSpec, int heightUsed) {


		// 1 ....	
			
		// 2 getChildMeasureSpec方法
        final int childWidthMeasureSpec = getChildMeasureSpec(parentWidthMeasureSpec,
                mPaddingLeft + mPaddingRight + lp.leftMargin + lp.rightMargin
                        + widthUsed, lp.width);
	}		

 

調用此方法處，看看這三個參數的具體含義。
1. spec ： 此視圖要求的規格 【parentWidthMeasureSpec】
2. padding ： 當前ViewGroup視圖的padding值與傳入子視圖的margin值 【mPaddingLeft + mPaddingRight + lp.leftMargin + lp.rightMargin + widthUsed】？widthUsed
3. childDimension : 傳入參數的視圖，期望展示多大【lp.width】

** 舉一個例子

擴展：MeasureSpec方法與拼接方式

 

 

 

    /**
     * Utility to reconcile a desired size with constraints imposed by a MeasureSpec.
     * Will take the desired size, unless a different size is imposed by the constraints.
     *
     * @param size How big the view wants to be
     * @param measureSpec Constraints imposed by the parent
     * @return The size this view should be.
     */
    public static int resolveSize(int size, int measureSpec) {
        int result = size;
        int specMode = MeasureSpec.getMode(measureSpec);
        int specSize =  MeasureSpec.getSize(measureSpec);
        switch (specMode) {
        case MeasureSpec.UNSPECIFIED:
            result = size;
            break;
        case MeasureSpec.AT_MOST:
            result = Math.min(size, specSize);
            break;
        case MeasureSpec.EXACTLY:
            result = specSize;
            break;
        }
        return result;
    }

 

 

 

        /**
         * Creates a measure specification based on the supplied size and mode.
         *
         * The mode must always be one of the following:
         * 

• *
• {@link android.view.View.MeasureSpec#UNSPECIFIED}
• *
• {@link android.view.View.MeasureSpec#EXACTLY}
• *
• {@link android.view.View.MeasureSpec#AT_MOST}
• *

* * @param size the size of the measure specification * @param mode the mode of the measure specification * @return the measure specification based on size and mode */ public static int makeMeasureSpec(int size, int mode) { return size + mode; }

 

 

    /**
     * 

This mehod must be called by {@link #onMeasure(int, int)} to store the * measured width and measured height. Failing to do so will trigger an * exception at measurement time.

* * @param measuredWidth the measured width of this view * @param measuredHeight the measured height of this view */ protected final void setMeasuredDimension(int measuredWidth, int measuredHeight) { mMeasuredWidth = measuredWidth; mMeasuredHeight = measuredHeight; mPrivateFlags |= MEASURED_DIMENSION_SET; } /** * The width of this view as measured in the most recent call to measure(). * This should be used during measurement and layout calculations only. Use * {@link #getWidth()} to see how wide a view is after layout. * * @return The measured width of this view. */ public final int getMeasuredWidth() { return mMeasuredWidth; } /** * The height of this view as measured in the most recent call to measure(). * This should be used during measurement and layout calculations only. Use * {@link #getHeight()} to see how tall a view is after layout. * * @return The measured height of this view. */ public final int getMeasuredHeight() { return mMeasuredHeight; }

 

 

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