ScrollView在测量子布局的时候会用UNSPECIFIED。

通过源码观察#xff0c;

Overrideprotected

heightMe…当我们在使用到ScrollView和ListView的时候可能会出现显示不全的问题。

那我们可以进行以下分析

ScrollView在测量子布局的时候会用UNSPECIFIED。

通过源码观察

Overrideprotected

{super.onMeasure(widthMeasureSpec,

(!mFillViewport)

MeasureSpec.getMode(heightMeasureSpec);if

(heightMode

getContext().getApplicationInfo().targetSdkVersion;final

(LayoutParams)

getChildMeasureSpec(widthMeasureSpec,

widthPadding,

MeasureSpec.makeMeasureSpec(desiredHeight,

MeasureSpec.EXACTLY);child.measure(childWidthMeasureSpec,

点击super.onMeasure()方法可以观察到进入了FrameLayout中

Overrideprotected

MeasureSpec.getMode(widthMeasureSpec)

MeasureSpec.EXACTLY

||MeasureSpec.getMode(heightMeasureSpec)

MeasureSpec.EXACTLY;mMatchParentChildren.clear();int

maxHeight

{measureChildWithMargins(child,

widthMeasureSpec,

child.getLayoutParams();maxWidth

Math.max(maxWidth,child.getMeasuredWidth()

lp.leftMargin

Math.max(maxHeight,child.getMeasuredHeight()

lp.topMargin

combineMeasuredStates(childState,

{if

{mMatchParentChildren.add(child);}}}}//

Account

getPaddingRightWithForeground();maxHeight

getPaddingBottomWithForeground();//

Check

getSuggestedMinimumHeight());maxWidth

Math.max(maxWidth,

drawable.getMinimumHeight());maxWidth

Math.max(maxWidth,

drawable.getMinimumWidth());}setMeasuredDimension(resolveSizeAndState(maxWidth,

widthMeasureSpec,

childState),resolveSizeAndState(maxHeight,

MEASURED_HEIGHT_STATE_SHIFT));count

(count

mMatchParentChildren.get(i);final

MarginLayoutParams

getPaddingRightWithForeground()-

lp.leftMargin

lp.rightMargin);childWidthMeasureSpec

MeasureSpec.makeMeasureSpec(width,

else

getChildMeasureSpec(widthMeasureSpec,getPaddingLeftWithForeground()

getPaddingRightWithForeground()

lp.leftMargin

lp.rightMargin,lp.width);}final

int

getPaddingBottomWithForeground()-

lp.topMargin

lp.bottomMargin);childHeightMeasureSpec

MeasureSpec.makeMeasureSpec(height,

else

getChildMeasureSpec(heightMeasureSpec,getPaddingTopWithForeground()

getPaddingBottomWithForeground()

lp.topMargin

lp.bottomMargin,lp.height);}child.measure(childWidthMeasureSpec,

childHeightMeasureSpec);}}}里面有个measureChildWithMargins方法

protected

getChildMeasureSpec(parentWidthMeasureSpec,mPaddingLeft

mPaddingRight

getChildMeasureSpec(parentHeightMeasureSpec,mPaddingTop

mPaddingBottom

lp.height);child.measure(childWidthMeasureSpec,

childHeightMeasureSpec);}这个时候发现ScrollView有重写这个方法

Overrideprotected

getChildMeasureSpec(parentWidthMeasureSpec,mPaddingLeft

mPaddingRight

MeasureSpec.makeSafeMeasureSpec(Math.max(0,

MeasureSpec.getSize(parentHeightMeasureSpec)

usedTotal),MeasureSpec.UNSPECIFIED);child.measure(childWidthMeasureSpec,

childHeightMeasureSpec);}其中childHeightMeasureSpec的模式是MeasureSpec.UNSPECIFIED。

这个表示尽可能的大很少能用到。

Overrideprotected

mListPaddingsuper.onMeasure(widthMeasureSpec,

int

MeasureSpec.getMode(widthMeasureSpec);final

int

MeasureSpec.getMode(heightMeasureSpec);int

widthSize

MeasureSpec.getSize(widthMeasureSpec);int

heightSize

MeasureSpec.getSize(heightMeasureSpec);int

childWidth

height.measureScrapChild(child,

widthMeasureSpec,

child.getMeasuredWidth();childHeight

child.getMeasuredHeight();childState

combineMeasuredStates(childState,

(recycleOnMeasure()

mRecycler.shouldRecycleViewType(((LayoutParams)

child.getLayoutParams()).viewType))

0);}}if

measureHeightOfChildren(widthMeasureSpec,

NO_POSITION,

-1);}setMeasuredDimension(widthSize,

widthMeasureSpec;}其中的heightMeasureSpec也就是我们在ScrollView中child.measure(childWidthMeasureSpec,

childHeightMeasureSpec);在传递过来的。

所以也是模式为MeasureSpec.UNSPECIFIED。

而当heightMode

(heightMode

所以要解决这个问题应该让listView进入heightMode

public

defStyleAttr);}Overrideprotected

void

{//解决显示不全的问题heightMeasureSpecMeasureSpec.makeMeasureSpec(Integer.MAX_VALUE2,MeasureSpec.AT_MOST);super.onMeasure(widthMeasureSpec,

heightMeasureSpec);}

网上有的博客换成MyListView这么做就实现了那么为什么呢

(heightMode

measureHeightOfChildren(widthMeasureSpec,

NO_POSITION,

-1);}调用ListView的measureHeightOfChildren

UnsupportedAppUsage(maxTargetSdk

trackingBug

isScrap);measureScrapChild(child,

widthMeasureSpec,

recycleBin.shouldRecycleViewType(((LayoutParams)

child.getLayoutParams()).viewType))

{recycleBin.addScrapView(child,

-1);}returnedHeight

returnedHeight;}因为returnedHeight一直在累加这样我们让maxHeight为最大值这样他就不会进入if

(returnedHeight

onMeasure方法中的widthMeasureSpec和heightMeasureSpec会包含两个信息第一个信息是模式2位第二个信息是值30位。

一共32位

要右移两位

MODE_MASK);}}因为Integer.MAX_VALUE右移两位等于一个30位的值这样执行makeMeasureSpec就可以构建成一个32位的值。

这样去替换ListView的heightMeasureSpec即可。

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