Android View 默認的onMeasure

lp 其實就是上個博客提到的Window Attribute 只不過是VIEwRoot的。

　　Java代碼

　　childWidthMeasureSpec = getRootMeasureSpec(desiredWindowWidth, lp.width);

　　childHeightMeasureSpec = getRootMeasureSpec(desiredWindowHeight, lp.height);

　　desiredWindowWidth 根據代碼可知，一般情況就是屏幕的寬度;desiredWindowHeight 根據代碼可知，一般情況就是屏幕的寬度-狀態欄高度;

　　/**

　　* Figures out the measure spec for the root vIEw in a window based on it's

　　* layout params.

　　*

　　* @param Windowsize

　　* The available width or height of the window

　　*

　　* @param rootDimension

　　* The layout params for one dimension (width or height) of the

　　* window.

　　*

　　* @return The measure spec to use to measure the root vIEw.

　　*/

　　private int getRootMeasureSpec(int Windowsize, int rootDimension) {

　　int measureSpec;

　　switch (rootDimension) {

　　case VIEwGroup.LayoutParams.MATCH_PARENT:

　　// Window can't resize. Force root vIEw to be Windowsize.

　　measureSpec = MeasureSpec.makeMeasureSpec(Windowsize, MeasureSpec.EXACTLY);

　　break;

　　case VIEwGroup.LayoutParams.WRAP_CONTENT:

　　// Window can resize. Set max size for root vIEw.

　　measureSpec = MeasureSpec.makeMeasureSpec(Windowsize, MeasureSpec.AT_MOST);

　　break;

　　default:

　　// Window wants to be an exact size. Force root vIEw to be that size.

　　measureSpec = MeasureSpec.makeMeasureSpec(rootDimension, MeasureSpec.EXACTLY);

　　break;

　　}

　　return measureSpec;

　　}

　　host.measure(childWidthMeasureSpec, childHeightMeasureSpec);

　　childWidthMeasureSpec = getRootMeasureSpec(desiredWindowWidth, lp.width);

　　childHeightMeasureSpec = getRootMeasureSpec(desiredWindowHeight,

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lp.height);

　　desiredWindowWidth 根據代碼可知，一般情況就是屏幕的寬度;desiredWindowHeight 根據代碼可知，一般情況就是屏幕的寬度-狀態欄高度;

　　/**

　　* Figures out the measure spec for the root vIEw in a window based on it's

　　* layout params.

　　*

　　* @param Windowsize

　　* The available width or height of the window

　　*

　　* @param rootDimension

　　* The layout params for one dimension (width or height) of the

　　* window.

　　*

　　* @return The measure spec to use to measure the root vIEw.

　　*/

　　private int getRootMeasureSpec(int Windowsize, int rootDimension) {

　　int measureSpec;

　　switch (rootDimension) {

　　case VIEwGroup.LayoutParams.MATCH_PARENT:

　　// Window can't resize. Force root vIEw to be Windowsize.

　　measureSpec = MeasureSpec.makeMeasureSpec(Windowsize, MeasureSpec.EXACTLY);

　　break;

　　case VIEwGroup.LayoutParams.WRAP_CONTENT:

　　// Window can resize. Set max size for root vIEw.

　　measureSpec = MeasureSpec.makeMeasureSpec(Windowsize, MeasureSpec.AT_MOST);

　　break;

　　default:

　　// Window wants to be an exact size. Force root vIEw to be that size.

　　measureSpec = MeasureSpec.makeMeasureSpec(rootDimension, MeasureSpec.EXACTLY);

　　break;

　　}

　　return measureSpec;

　　}

　　host.measure(childWidthMeasureSpec, childHeightMeasureSpec);

　　注意ViewRoot並不是View，不過是ViewParent。刷新屏幕都是在這個類中，host就是PhoneWindow的DecorVIEw。

　　Java代碼

　　protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {

　　setMeasuredDimension(getDefaultSize(getSuggestedMinimumWidth(), widthMeasureSpec),

　　getDefaultSize(getSuggestedMinimumHeight(), heightMeasureSpec));

　　}

　　/**

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　　* Utility to return a default size. Uses the supplIEd size if the

　　* MeasureSpec imposed no contraints. Will get larger if allowed

　　* by the MeasureSpec.

　　*

　　* @param size Default size for this vIEw

　　* @param measureSpec Constraints imposed by the parent

　　* @return The size this vIEw should be.

　　*/

　　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;

　　}

　　protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {

　　setMeasuredDimension(getDefaultSize(getSuggestedMinimumWidth(), widthMeasureSpec),

　　getDefaultSize(getSuggestedMinimumHeight(), heightMeasureSpec));

　　}

　　/**

　　* Utility to return a default size. Uses the supplIEd size if the

　　* MeasureSpec imposed no contraints. Will get larger if allowed

　　* by the MeasureSpec.

　　*

　　* @param size Default size for this vIEw

　　* @param measureSpec Constraints imposed by the parent

　　* @return The size this vIEw should be.

　　*/

　　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;

　　}