洛阳 网站建设公司,吉林省建设安全协会网站,招商网站,百度网站建设目标1. MeasureSpec类
MeasureSpec用来计算子视图的大小#xff0c;有三种类型#xff0c;UNSPECIFIED、EXACTLY和AT_MOST。
UNSPECIFIED表示未定义#xff0c;即父控件未做限制#xff0c;可以为任何值#xff0c;一般设置为0。EXACTLY表示实际值#xff0c;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 cant 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 cant 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);
}相关文章 Android 自定义流式布局 Android measure方法详解
