Android MeasureSpec 의 이해 와 소스 코드 분석
13531 단어 AndroidMeasureSpec
MeasureSpec 생 성 규칙:
실례 설명:
package cc.ww;
import android.view.View;
import android.view.View.MeasureSpec;
import android.view.ViewGroup.LayoutParams;
import android.view.ViewGroup.MarginLayoutParams;
import android.widget.LinearLayout;
/**
* @author http://blog.csdn.net/lfdfhl
*
* :
* MeasureSpec
*
* (1) MeasureSpec
* MeasureSpec " ", 32 int .
* 2 SpecMode , 32 SpecSize .
* :
* int specMode = MeasureSpec.getMode(measureSpec) specMode
int specSize = MeasureSpec.getSize(measureSpec) SpecSize
SpecMode :
MeasureSpec.EXACTLY
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.
View . View SpecSize.
(1) View LayoutParams ( ) ( 100px) MeasureSpec MeasureSpec.EXACTLY
MeasureSpec.AT_MOST MeasureSpec.UNSPECIFIED :
View specMode MeasureSpec.EXACTLY
View specSize View (childSize)
:
View LayoutParams ( ) ( 100px) , View , px
. specMode , View specMode MeasureSpec.EXACTLY,
View specSize View (childSize).
(2) View LayoutParams ( ) match_parent MeasureSpec MeasureSpec.EXACTLY :
View specMode MeasureSpec.EXACTLY
View specSize (parentLeftSize)
:
View LayoutParams ( ) match_parent MeasureSpec MeasureSpec.EXACTLY.
View : , View .
, MeasureSpec MeasureSpec.EXACTLY :
View specMode MeasureSpec.EXACTLY, .
View specSize (parentLeftSize), .
,MeasureSpec MeasureSpec.AT_MOST ？
View specMode MeasureSpec.AT_MOST, .
View specSize (parentLeftSize), .
MeasureSpec.AT_MOST
The child can be as large as it wants up to the specified size.
specSize, View .
(1) View LayoutParams ( ) match_parent MeasureSpec MeasureSpec.AT_MOST :
View specMode MeasureSpec.AT_MOST
View specSize (parentLeftSize)
MeasureSpec.EXACTLY .
(2) View LayoutParams ( ) wrap_content MeasureSpec MeasureSpec.EXACTLY :
View specMode MeasureSpec.AT_MOST
View specSize (parentLeftSize)
:
View LayoutParams ( ) wrap_content View , content .
MeasureSpec MeasureSpec.EXACTLY ;
View , ,
View specMode MeasureSpec.AT_MOST
View specSize (parentLeftSize)
(3) View LayoutParams ( ) wrap_content MeasureSpec MeasureSpec.AT_MOST :
View specMode MeasureSpec.AT_MOST
View specSize (parentLeftSize)
:
View LayoutParams ( ) wrap_content View , content .
MeasureSpec MeasureSpec.AT_MOST
View , ,
View specMode MeasureSpec.AT_MOST
View specSize (parentLeftSize)
MeasureSpec.UNSPECIFIED
The parent has not imposed any constraint on the child. It can be whatever size it wants.
View .
Android , ListView ScrollView. .
, .
* (2) onMeasure() View MeasureSpec
* , .
*
*/
public class UnderstandMeasureSpec {
/**
* :
* ViewGroup View measureChildWithMargins() , .
* :
* @param child
* View
* @param parentWidthMeasureSpec
* ( LinearLayout) MeasureSpec
* @param widthUsed
* ( LinearLayout)
* @param parentHeightMeasureSpec
* ( LinearLayout) MeasureSpec
* @param heightUsed
* ( LinearLayout)
*
* , getChildMeasureSpec()
* View MeasureSpec.
*/
protected void measureChildWithMargins(View child,int parentWidthMeasureSpec, int widthUsed,
int parentHeightMeasureSpec, int heightUsed) {
//1 View LayoutParams
final MarginLayoutParams lp = (MarginLayoutParams) child.getLayoutParams();
//2 View MeasureSpec
final int childWidthMeasureSpec = getChildMeasureSpec
(parentWidthMeasureSpec,mPaddingLeft + mPaddingRight + lp.leftMargin + lp.rightMargin + widthUsed, lp.width);
//3 View MeasureSpec
final int childHeightMeasureSpec = getChildMeasureSpec
(parentHeightMeasureSpec,mPaddingTop + mPaddingBottom + lp.topMargin + lp.bottomMargin + heightUsed, lp.height);
//4 View
child.measure(childWidthMeasureSpec, childHeightMeasureSpec);
}
/**
* getChildMeasureSpec() View MeasureSpec
* :
* @param spec
* ( LinearLayout) MeasureSpec
* @param padding
* ( LinearLayout) .
* measureChildWithMargins() getChildMeasureSpec() :
* :mPaddingLeft + mPaddingRight + lp.leftMargin + lp.rightMargin
* :
* mPaddingLeft mPaddingRight padding
* lp.leftMargin lp.rightMargin View margin
* View. :
*
* :
* mPaddingTop + mPaddingBottom + lp.topMargin + lp.bottomMargin
* :
* ( LinearLayout) .
* @param childDimension
* View LayoutParams View
*
*
* getChildMeasureSpec() :
* ( LinearLayout) MeasureSpec View LayoutParams View MeasureSpec！！！
*
*
*
*/
public static int getChildMeasureSpec(int spec, int padding, int childDimension) {
/**
* : specMode specSize
*/
int specMode = MeasureSpec.getMode(spec);
int specSize = MeasureSpec.getSize(spec);
/**
* : .
* padding
*/
int size = Math.max(0, specSize - padding);
int resultSize = 0;
int resultMode = 0;
/**
* : View specMode specSize.
* .
*/
switch (specMode) {
/**
* :
* EXACTLY
*
* :
* LayoutParams.MATCH_PARENT=-1
* LayoutParams.WRAP_CONTENT=-2
* :
* childDimension >= 0 View MATCH_PARENT WRAP_CONTENT
*/
case MeasureSpec.EXACTLY:
/**
* EXACTLY :
* View , 100px;
* :
* View size childDimension
* View mode MeasureSpec.EXACTLY
*/
if (childDimension >= 0) {
resultSize = childDimension;
resultMode = MeasureSpec.EXACTLY;
/**
* EXACTLY :
* View LayoutParams.MATCH_PARENT
* :
* View size size
* View mode MeasureSpec.EXACTLY
*/
} else if (childDimension == LayoutParams.MATCH_PARENT) {
// Child wants to be our size. So be it.
resultSize = size;
resultMode = MeasureSpec.EXACTLY;
/**
* EXACTLY :
* View LayoutParams.WRAP_CONTENT
* :
* View size size
* View mode 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;
/**
* :
* AT_MOST
*
* :pp
* LayoutParams.MATCH_PARENT=-1
* LayoutParams.WRAP_CONTENT=-2
* :
* childDimension >= 0 View MATCH_PARENT WRAP_CONTENT
*/
case MeasureSpec.AT_MOST:
/**
* AT_MOST :
* View , 100px;
* :
* View size childDimension
* View mode MeasureSpec.EXACTLY
*/
if (childDimension >= 0) {
// Child wants a specific size... so be it
resultSize = childDimension;
resultMode = MeasureSpec.EXACTLY;
/**
* AT_MOST :
* View LayoutParams.MATCH_PARENT
* :
* View size size
* View mode MeasureSpec.AT_MOST
*/
} 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;
/**
* AT_MOST :
* View LayoutParams.WRAP_CONTENT
* :
* View size size
* View mode 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;
/**
* :
* UNSPECIFIED
*
* :
* LayoutParams.MATCH_PARENT=-1
* LayoutParams.WRAP_CONTENT=-2
* :
* childDimension >= 0 View MATCH_PARENT WRAP_CONTENT
*/
case MeasureSpec.UNSPECIFIED:
/**
* UNSPECIFIED :
* View , 100px;
* :
* View size childDimension
* View mode MeasureSpec.EXACTLY
*/
if (childDimension >= 0) {
// Child wants a specific size... let him have it
resultSize = childDimension;
resultMode = MeasureSpec.EXACTLY;
/**
* UNSPECIFIED :
* View LayoutParams.MATCH_PARENT
* :
* View size 0
* View mode MeasureSpec.UNSPECIFIED
*/
} else if (childDimension == LayoutParams.MATCH_PARENT) {
// Child wants to be our size... find out how big it should be
resultSize = 0;
resultMode = MeasureSpec.UNSPECIFIED;
/**
* UNSPECIFIED :
* View LayoutParams.WRAP_CONTENT
* :
* View size 0
* View mode MeasureSpec.UNSPECIFIED
*/
} else if (childDimension == LayoutParams.WRAP_CONTENT) {
// Child wants to determine its own size.... find out how big it should be
resultSize = 0;
resultMode = MeasureSpec.UNSPECIFIED;
}
break;
}
return MeasureSpec.makeMeasureSpec(resultSize, resultMode);
}
}
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