作用
类似于自定义布局
职责
ViewGroup相当于一个放置View的容器，并且我们在写布局xml的时候，会告诉容器（凡是以layout为开头的属性，都是为用于告诉容器的），我们的宽度（layout_width）、高度（layout_height）、对齐方式（layout_gravity）等；当然还有margin等；于是乎，ViewGroup的职能为：给childView计算出建议的宽和高和测量模式 ；决定childView的位置；为什么只是建议的宽和高，而不是直接确定呢，别忘了childView宽和高可以设置为wrap_content，这样只有childView才能计算出自己的宽和高。
步骤
- 决定该ViewGroup的LayoutParams
- 重写onMeasure方法
- 重写onLayout方法
- 使用该布局
完整代码实例
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| class ViewLayout(context: Context, attrs: AttributeSet?):ViewGroup(context,attrs) {
override fun generateLayoutParams(attrs: AttributeSet?): ViewGroup.LayoutParams {
return MarginLayoutParams(context,attrs)
}
override fun onMeasure(widthMeasureSpec: Int, heightMeasureSpec: Int) {
val widthMode = MeasureSpec.getMode(widthMeasureSpec)
val heightMode = MeasureSpec.getMode(heightMeasureSpec)
val sizeWidth = MeasureSpec.getSize(widthMeasureSpec)
val sizeHeight = MeasureSpec.getSize(heightMeasureSpec)
measureChildren(widthMeasureSpec, heightMeasureSpec)
var width = 0
var height = 0
val cCount = childCount
var cWidth = 0
var cHeight = 0
var cParams: MarginLayoutParams? = null
var lHeight = 0
var rHeight = 0
var tWidth = 0
var bWidth = 0
for (i in 0..<cCount) {
val childView = getChildAt(i)
cWidth = childView.measuredWidth
cHeight = childView.measuredHeight
cParams = childView.layoutParams as MarginLayoutParams
if (i == 0 || i == 1) {
tWidth += cWidth + cParams!!.leftMargin + cParams!!.rightMargin
}
if (i == 2 || i == 3) {
bWidth += cWidth + cParams!!.leftMargin + cParams!!.rightMargin
}
if (i == 0 || i == 2) {
lHeight += cHeight + cParams!!.topMargin + cParams!!.bottomMargin
}
if (i == 1 || i == 3) {
rHeight += cHeight + cParams!!.topMargin + cParams!!.bottomMargin
}
}
width = max(tWidth.toDouble(), bWidth.toDouble()).toInt()
height = max(lHeight.toDouble(), rHeight.toDouble()).toInt()
setMeasuredDimension(
if (widthMode == MeasureSpec.EXACTLY)
sizeWidth
else
width, if (heightMode == MeasureSpec.EXACTLY)
sizeHeight
else
height
)
}
override fun onLayout(changed: Boolean, l: Int, t: Int, r: Int, b: Int) {
val cCount = childCount
var cWidth = 0
var cHeight = 0
var cParams: MarginLayoutParams? = null
for (i in 0..<cCount) {
val childView = getChildAt(i)
cWidth = childView.measuredWidth
cHeight = childView.measuredHeight
cParams = childView.layoutParams as MarginLayoutParams
var cl = 0
var ct = 0
var cr = 0
var cb = 0
when (i) {
0 -> {
cl = cParams!!.leftMargin
ct = cParams!!.topMargin
}
1 -> {
cl = (width - cWidth - cParams!!.rightMargin)
ct = cParams!!.topMargin
}
2 -> {
cl = cParams!!.leftMargin
ct = height - cHeight - cParams!!.bottomMargin
}
3 -> {
cl = (width - cWidth - cParams!!.rightMargin)
ct = height - cHeight - cParams!!.bottomMargin
}
}
cr = cl + cWidth
cb = cHeight + ct
childView.layout(cl, ct, cr, cb)
}
}
}
|
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| <com.example.studyviewgrope.ViewLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="#AA333333" >
<TextView
android:layout_width="150dp"
android:layout_height="150dp"
android:background="#E5ED05"
android:gravity="center"
android:text="0"
android:textColor="#FFFFFF"
android:textSize="22sp"
android:textStyle="bold" />
<TextView
android:layout_width="50dp"
android:layout_height="50dp"
android:background="#00ff00"
android:gravity="center"
android:text="1"
android:textColor="#FFFFFF"
android:textSize="22sp"
android:textStyle="bold" />
<TextView
android:layout_width="50dp"
android:layout_height="50dp"
android:background="#ff0000"
android:gravity="center"
android:text="2"
android:textColor="#FFFFFF"
android:textSize="22sp"
android:textStyle="bold" />
<TextView
android:layout_width="150dp"
android:layout_height="150dp"
android:background="#0000ff"
android:gravity="center"
android:text="3"
android:textColor="#FFFFFF"
android:textSize="22sp"
android:textStyle="bold" />
</com.example.studyviewgrope.ViewLayout>
|
