Android ScrollView嵌套ListView显示不全问题
未嵌套ScrollView的ListView显示正常显示全
一旦嵌套了ScrollView
只显示了一行item的高度，显示不全
通过查看源码发现
因为ScrollView和ListView的heightMeasureSpec都是MeasureSpec.UNSPECIFIED
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
// MeasureSpec有父级传进来，因为ScrollView为MeasureSpec.UNSPECIFIED所以这里的heightMode == MeasureSpec.UNSPECIFIED
final int widthMode = MeasureSpec.getMode(widthMeasureSpec);
final int heightMode = MeasureSpec.getMode(heightMeasureSpec);
int widthSize = MeasureSpec.getSize(widthMeasureSpec);
int heightSize = MeasureSpec.getSize(heightMeasureSpec);
int childWidth = 0;
int childHeight = 0;
int childState = 0;
mItemCount = mAdapter == null ? 0 : mAdapter.getCount();
if (mItemCount > 0 && (widthMode == MeasureSpec.UNSPECIFIED
|| heightMode == MeasureSpec.UNSPECIFIED)) {
final View child = obtainView(0, mIsScrap);
measureScrapChild(child, 0, widthMeasureSpec, heightSize);
childWidth = child.getMeasuredWidth();
childHeight = child.getMeasuredHeight();
childState = combineMeasuredStates(childState, child.getMeasuredState());
if (recycleOnMeasure() && mRecycler.shouldRecycleViewType(
((LayoutParams) child.getLayoutParams()).viewType)) {
mRecycler.addScrapView(child, 0);
}
}
if (widthMode == MeasureSpec.UNSPECIFIED) {
widthSize = mListPadding.left + mListPadding.right + childWidth +
getVerticalScrollbarWidth();
} else {
widthSize |= (childState & MEASURED_STATE_MASK);
}
// 因为ListView的模式也是MeasureSpec.UNSPECIFIED，所以导致进入if
if (heightMode == MeasureSpec.UNSPECIFIED) {
// 高度就为一个的高度childHeight
heightSize = mListPadding.top + mListPadding.bottom + childHeight +
getVerticalFadingEdgeLength() * 2;
}
if (heightMode == MeasureSpec.AT_MOST) {
heightSize = measureHeightOfChildren(widthMeasureSpec, 0, NO_POSITION, heightSize, -1);
}
setMeasuredDimension(widthSize, heightSize);
mWidthMeasureSpec = widthMeasureSpec;
}
所以导致显示不全是因是heightMode == MeasureSpec.UNSPECIFIED进入了
if (heightMode == MeasureSpec.UNSPECIFIED) {
// 高度就为一个的高度childHeight
heightSize = mListPadding.top + mListPadding.bottom + childHeight +
getVerticalFadingEdgeLength() * 2;
}
导致heightSize 被重新赋值为了一个childHeight 的高度
解决方法：
自己继承一个ListView重写onMeasure，通过MeasureSpec.makeMeasureSpec()方法来设置heightMode使他设置为MeasureSpec.AT_MOST
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
// 将模式设置为MeasureSpec.AT_MOST
heightMeasureSpec = MeasureSpec.makeMeasureSpec(Integer.MAX_VALUE>>2,MeasureSpec.AT_MOST);
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
}
Integer.MAX_VALUE>>2 ：
因为MeasureSpec 一个值表示了两个值，最高两位代表模式，后面代表的是尺寸
而这边makeMeasureSpec传的第一个参数是给子级的最大尺寸，所以右移两位就是能给子级最大的高度，所以解决了显示不全的问题
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