怎么查网站是否被k/上海还能推seo吗

前言

在上一篇我们了解了Activity的构成后，开始了解一下View的工作流程，就是measure、layout和draw。measure用来测量View的宽高，layout用来确定View的位置，draw则用来绘制View。这一讲我们来看看measure流程，measure流程分为View的measure流程和ViewGroup的measure流程，只不过ViewGroup的measure流程除了要完成自己的测量还要遍历去调用子元素的measure()方法。

1.View的measure流程

先来看看onMeasure()方法（View.java）：

protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {setMeasuredDimension(getDefaultSize(getSuggestedMinimumWidth(), widthMeasureSpec),getDefaultSize(getSuggestedMinimumHeight(), heightMeasureSpec));}

看看setMeasuredDimension()方法：

protected final void setMeasuredDimension(int measuredWidth, int measuredHeight) {boolean optical = isLayoutModeOptical(this);if (optical != isLayoutModeOptical(mParent)) {Insets insets = getOpticalInsets();int opticalWidth  = insets.left + insets.right;int opticalHeight = insets.top  + insets.bottom;measuredWidth  += optical ? opticalWidth  : -opticalWidth;measuredHeight += optical ? opticalHeight : -opticalHeight;}setMeasuredDimensionRaw(measuredWidth, measuredHeight);}

很显然是用来设置View的宽高的，先来看看getDefaultSize()方法处理了什么：

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:result = size;break;case MeasureSpec.AT_MOST:case MeasureSpec.EXACTLY:result = specSize;break;}return result;
}

specMode是View的测量模式，而specSize是View的测量大小，看到这里我们有必要先看看MeasureSpec类：

public static class MeasureSpec {private static final int MODE_SHIFT = 30;private static final int MODE_MASK  = 0x3 << MODE_SHIFT;/*** Measure specification mode: The parent has not imposed any constraint* on the child. It can be whatever size it wants.*/public static final int UNSPECIFIED = 0 << MODE_SHIFT;/*** Measure specification mode: The parent has determined an exact size* for the child. The child is going to be given those bounds regardless* of how big it wants to be.*/public static final int EXACTLY     = 1 << MODE_SHIFT;/*** Measure specification mode: The child can be as large as it wants up* to the specified size.*/public static final int AT_MOST     = 2 << MODE_SHIFT;...public static int getMode(int measureSpec) {return (measureSpec & MODE_MASK);}public static int getSize(int measureSpec) {return (measureSpec & ~MODE_MASK);}
...        
}

MeasureSpec类帮助我们来测量View，它是一个32位的int值，高两位为specMode （测量的模式），低30位为specSize （测量的大小），测量模式分为三种：

• UNSPECIFIED：未指定模式，View想多大就多大，父容器不做限制，一般用于系统内部的测量。
• AT_MOST：最大模式，对应于wrap_comtent属性，只要尺寸不超过父控件允许的最大尺寸就行。
• EXACTLY：精确模式，对应于match_parent属性和具体的数值，父容器测量出View所需要的大小，也就是specSize的值。

让我们回头看看getDefaultSize()方法，很显然在AT_MOST和EXACTLY模式下，都返回specSize这个值，也就是View测量后的大小，而在UNSPECIFIED模式返回的是getDefaultSize()方法的第一次个参数的值，这第一个参数从onMeasure()方法来看是getSuggestedMinimumWidth()方法和getSuggestedMinimumHeight()得到的，那我们来看看getSuggestedMinimumWidth()方法做了什么，我们只需要弄懂getSuggestedMinimumWidth()方法，因为这两个方法原理是一样的：

protected int getSuggestedMinimumWidth() {return (mBackground == null) ? mMinWidth : max(mMinWidth, mBackground.getMinimumWidth());}

如果View没有设置背景则取值为mMinWidth，mMinWidth是可以设置的，它对应于android:minWidth这个属性设置的值或者View的setMinimumWidth的值，如果不指定的话则默认为0：

public void setMinimumWidth(int minWidth) {mMinWidth = minWidth;requestLayout();
}

如果View设置了背景在取值为max(mMinWidth, mBackground.getMinimumWidth())，取值mMinWidth和mBackground.getMinimumWidth()的最大值，上面我们说过了mMinWidth，那来看看mBackground.getMinimumWidth()，这个mBackground是Drawable类型的，看一下Drawable类的getMinimumWidth()方法（Drawable.java）：

public int getMinimumWidth() {final int intrinsicWidth = getIntrinsicWidth();return intrinsicWidth > 0 ? intrinsicWidth : 0;
}

intrinsicWidth得到的是这个Drawable的固有的宽度，如果固有宽度大于0则返回固有宽度，否则返回0。
总结一下getSuggestedMinimumWidth()方法就是：如果View没有设置背景则返回mMinWidth ，如果设置了背景就返回mMinWidth 和Drawable最小宽度两个值的最大值。

2.ViewGroup的measure流程

ViewGroup的measure原理

讲完了View的measure流程，接下来看看ViewGroup的measure流程，对于ViewGroup，它不只要measure自己本身，还要遍历的调用子元素的measure()方法，ViewGroup中没有定义onMeasure()方法，但他定义了measureChildren()方法（ViewGroup.java）：

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);}}}

就是遍历子元素并调用measureChild()方法：

protected void measureChild(View child, int parentWidthMeasureSpec,int parentHeightMeasureSpec) {final LayoutParams lp = child.getLayoutParams();final int childWidthMeasureSpec = getChildMeasureSpec(parentWidthMeasureSpec,mPaddingLeft + mPaddingRight, lp.width);final int childHeightMeasureSpec = getChildMeasureSpec(parentHeightMeasureSpec,mPaddingTop + mPaddingBottom, lp.height);child.measure(childWidthMeasureSpec, childHeightMeasureSpec);}

调用child.getLayoutParams()方法来获得子元素的LayoutParams属性，并获取到子元素的MeasureSpec并调用子元素的measure()方法进行测量。getChildMeasureSpec()方法里写了什么呢？

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.MATCH_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.MATCH_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.MATCH_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);
}

很显然这是根据父容器的MeasureSpec的模式再结合子元素的LayoutParams属性来得出子元素的MeasureSpec属性，有一点需要注意的是如果父容器的MeasureSpec属性为AT_MOST，子元素的LayoutParams属性为WRAP_CONTENT，那根据代码我们会发现子元素的MeasureSpec属性也为AT_MOST，它的specSize值为父容器的specSize减去padding的值，也就是说跟这个子元素设置LayoutParams属性为MATCH_PARENT效果是一样的，为了解决这个问题需要在LayoutParams属性为WRAP_CONTENT时指定一下默认的宽和高。

LinearLayout的measure流程

ViewGroup并没有提供onMeasure()方法，而是让其子类来各自实现测量的方法，究其原因就是ViewGroup有不同的布局的需要很难统一，接下来我们来简单分析一下ViewGroup的子类LinearLayout的measure流程，先来看看它的onMeasure()方法（LinearLayout.java）：

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

来看看垂直measureVertical()方法的部分源码：

void measureVertical(int widthMeasureSpec, int heightMeasureSpec) {mTotalLength = 0;mTotalLength = 0;       ...for (int i = 0; i < count; ++i) {final View child = getVirtualChildAt(i);if (child == null) {mTotalLength += measureNullChild(i);continue;}if (child.getVisibility() == View.GONE) {i += getChildrenSkipCount(child, i);continue;}if (hasDividerBeforeChildAt(i)) {mTotalLength += mDividerHeight;}LinearLayout.LayoutParams lp = (LinearLayout.LayoutParams) child.getLayoutParams();totalWeight += lp.weight;if (heightMode == MeasureSpec.EXACTLY && lp.height == 0 && lp.weight > 0) {// Optimization: don't bother measuring children who are going to use// leftover space. These views will get measured again down below if// there is any leftover space.final int totalLength = mTotalLength;mTotalLength = Math.max(totalLength, totalLength + lp.topMargin + lp.bottomMargin);skippedMeasure = true;} else {int oldHeight = Integer.MIN_VALUE;if (lp.height == 0 && lp.weight > 0) {// heightMode is either UNSPECIFIED or AT_MOST, and this// child wanted to stretch to fill available space.// Translate that to WRAP_CONTENT so that it does not end up// with a height of 0oldHeight = 0;lp.height = LayoutParams.WRAP_CONTENT;}// Determine how big this child would like to be. If this or// previous children have given a weight, then we allow it to// use all available space (and we will shrink things later// if needed).
                measureChildBeforeLayout(child, i, widthMeasureSpec, 0, heightMeasureSpec,totalWeight == 0 ? mTotalLength : 0);if (oldHeight != Integer.MIN_VALUE) {lp.height = oldHeight;}final int childHeight = child.getMeasuredHeight();final int totalLength = mTotalLength;mTotalLength = Math.max(totalLength, totalLength + childHeight + lp.topMargin +lp.bottomMargin + getNextLocationOffset(child));
...if (useLargestChild &&(heightMode == MeasureSpec.AT_MOST || heightMode == MeasureSpec.UNSPECIFIED)) {mTotalLength = 0;for (int i = 0; i < count; ++i) {final View child = getVirtualChildAt(i);if (child == null) {mTotalLength += measureNullChild(i);continue;}if (child.getVisibility() == GONE) {i += getChildrenSkipCount(child, i);continue;}final LinearLayout.LayoutParams lp = (LinearLayout.LayoutParams)child.getLayoutParams();// Account for negative marginsfinal int totalLength = mTotalLength;mTotalLength = Math.max(totalLength, totalLength + largestChildHeight +lp.topMargin + lp.bottomMargin + getNextLocationOffset(child));}}// Add in our paddingmTotalLength += mPaddingTop + mPaddingBottom;int heightSize = mTotalLength;// Check against our minimum height

定义了mTotalLength用来存储LinearLayout在垂直方向的高度，然后遍历子元素，根据子元素的MeasureSpec模式分别计算每个子元素的高度，如果是wrap_content则将每个子元素的高度和margin垂直高度等值相加并赋值给mTotalLength得出整个LinearLayout的高度。如果布局高度设置为match_parent者具体数值则和View的测量方法一样。