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 类型转换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);}此方法针对第一个参数传递的子视图进行Measure操作。1. 传递的子视图LayoutParams必须是或者继承自MarginLayoutParams，否者会抛出转换异常 /*** 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 uscase 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 uscase MeasureSpec.AT_MOST:if (childDimension >= 0) {// Child wants a specific size… so be itresultSize = 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 becase MeasureSpec.UNSPECIFIED:if (childDimension >= 0) {// Child wants a specific size… let him have itresultSize = childDimension;resultMode = MeasureSpec.EXACTLY;} else if (childDimension == LayoutParams.FILL_PARENT) {// Child wants to be our size… find out how big it should// beresultSize = 0;resultMode = MeasureSpec.UNSPECIFIED;} else if (childDimension == LayoutParams.WRAP_CONTENT) {// Child wants to determine its own size…. find out how// big it should beresultSize = 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);}调用此方法处，，看看这三个参数的具体含义。1. spec ： 此视图要求的规格 【parentWidthMeasureSpec】2. padding ： 当前ViewGroup视图的padding值与传入子视图的margin值 【mPaddingLeft + mPaddingRight + lp.leftMargin + lp.rightMargin + widthUsed】？widthUsed3. childDimension : 传入参数的视图，期望展示多大【lp.width】** 举一个例子
扩展：MeasureSpec方法与拼接方式
勤勉是通往胜利的必经之路。要是由于胆怯艰难而去另觅佳径，
