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哪个网站可以做条形码,网络营销的现状及问题,更改wordpress所有的链接地址,怎样做网站 app教程1. MeasureSpec类 MeasureSpec用来计算子视图的大小，有三种类型，UNSPECIFIED、EXACTLY和AT_MOST。 UNSPECIFIED表示未定义，即父控件未做限制，可以为任何值，一般设置为0。EXACTLY表示实际值，即父容器已经指…

1. MeasureSpec类

MeasureSpec用来计算子视图的大小，有三种类型，UNSPECIFIED、EXACTLY和AT_MOST。

UNSPECIFIED表示未定义，即父控件未做限制，可以为任何值，一般设置为0。
EXACTLY表示实际值，即父容器已经指定了具体的值。
AT_MOST表示父容器提供了最大值，但子控件可以选择自己的范围。

使用静态方法来获取实际的mode和size

public static int getMode(int measureSpec)
public static int getSize(int measureSpec)

2. View的measure方法

measure(int, int)方法计算高宽，调用onMeasure(int, int)方法计算或setMeasuredDimensionRaw(int, int)方法设置。

public final void measure(int widthMeasureSpec, int heightMeasureSpec) {... ...int cacheIndex = forceLayout ? -1 : mMeasureCache.indexOfKey(key);if (cacheIndex < 0 || sIgnoreMeasureCache) {// measure ourselves, this should set the measured dimension flag backonMeasure(widthMeasureSpec, heightMeasureSpec);mPrivateFlags3 &= ~PFLAG3_MEASURE_NEEDED_BEFORE_LAYOUT;} else {long value = mMeasureCache.valueAt(cacheIndex);// Casting a long to int drops the high 32 bits, no mask neededsetMeasuredDimensionRaw((int) (value >> 32), (int) value);mPrivateFlags3 |= PFLAG3_MEASURE_NEEDED_BEFORE_LAYOUT;}... ...
}

onMeasure(int, int)方法，调用setMeasuredDimension(int, int)方法来设置实际的宽和高，getDefaultSize(int, int)方法获取默认的宽高。

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

在getDefaultSize(int, int)方法中，使用MeasureSpec来获取mode和size，并返回计算后的值。当mode为UNSPECIFIED时，返回默认值，否则返回建议值。

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;
}

setMeasuredDimension(int, int)方法同样调用setMeasuredDimensionRaw(int, int)方法设置宽高

protected final void setMeasuredDimension(int measuredWidth, int measuredHeight) {... ...setMeasuredDimensionRaw(measuredWidth, measuredHeight);
}

3. ViewGroup的measureChild方法

ViewGroup除了需要计算自身的宽高以外，还要计算子控件的宽高，系统提供了measureChildren(int, int)、measureChild(View, int, int)和getChildMeasureSpec(int, int, int)来支持一般的操作。

measureChildren(int, int)方法，只要child的Visibility不是GONE，就计算child的宽高，调用measureChild方法

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);}}
}

measureChild(View, int, int)方法，使用getChildMeasureSpec(int, int, int)方法获得宽高，最后调用View.measure(int, int)方法设置。

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);
}

getChildMeasureSpec(int, int, int)方法，根据ViewGroup的mode分为三种情况，如果childDimension大于0，则直接指定。

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 = View.sUseZeroUnspecifiedMeasureSpec ? 0 : size;resultMode = MeasureSpec.UNSPECIFIED;} else if (childDimension == LayoutParams.WRAP_CONTENT) {// Child wants to determine its own size.... find out how// big it should beresultSize = View.sUseZeroUnspecifiedMeasureSpec ? 0 : size;resultMode = MeasureSpec.UNSPECIFIED;}break;}//noinspection ResourceTypereturn MeasureSpec.makeMeasureSpec(resultSize, resultMode);
}