1.在方法onMeasure中调用setMeasuredDimension方法
setMeasuredDimension(int measuredWidth, int measuredHeight)
在onMeasure(int, int)中,必须调用setMeasuredDimension(int width, int height)来存储测量得到的宽度和高度值,如果没有这么去做会触发异常IllegalStateException。
2.在方法onMeasure中调用孩子的measure方法
measure(int widthMeasureSpec, int heightMeasureSpec)
这个方法用来测量出view的大小。父view使用width参数和height参数来提供constraint信息。实际上,view的测量工作在onMeasure(int, int)方法中完成。因此,只有onMeasure(int, int)方法可以且必须被重写。参数widthMeasureSpec提供view的水平空间的规格说明,参数heightMeasureSpec提供view的垂直空间的规格说明。
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
int width = MeasureSpec.getSize(widthMeasureSpec);
int height = MeasureSpec.getSize(heightMeasureSpec);
setMeasuredDimension(width, height);
for (int i = 0; i < getChildCount(); i++) {
getChildAt(i).measure(widthMeasureSpec, heightMeasureSpec);
}
}
3.解析onLayout(boolean, int, int, int, int)方法
onLayout(boolean changed, int l, int t, int r, int b)
调用场景:在view给其孩子设置尺寸和位置时被调用。子view,包括孩子在内,必须重写onLayout(boolean, int, int, int, int)方法,并且调用各自的layout(int, int, int, int)方法。
参数说明:参数changed表示view有新的尺寸或位置;参数l表示相对于父view的Left位置;参数t表示相对于父view的Top位置;参数r表示相对于父view的Right位置;参数b表示相对于父view的Bottom位置。.
@Override
protected void onLayout(boolean changed, int l, int t, int r, int b) {
int cWidth = 0;
int cHeight = 0;
MarginLayoutParams params = null;
for (int i = 0; i < getChildCount(); i++) {
View childView = getChildAt(i);
cWidth = childView.getMeasuredWidth();
cHeight = childView.getMeasuredHeight();
params = (MarginLayoutParams) childView.getLayoutParams();
int cl = 0;
int ct = 0;
int cr = 0;
int cb = 0;
switch (i) {
case 0:
cl = params.leftMargin;
ct = params.topMargin;
break;
case 1:
cl = getWidth() - cWidth - params.leftMargin - params.rightMargin;
ct = params.topMargin;
break;
case 2:
cl = params.leftMargin;
ct = getHeight() - cHeight - params.topMargin - params.bottomMargin;
break;
case 3:
cl = getWidth() - cWidth - params.leftMargin - params.rightMargin;
ct = getHeight() - cHeight - params.topMargin - params.bottomMargin;
break;
}
cr = cl + cWidth;
cb = ct + cHeight;
childView.layout(cl, ct, cr, cb);
}
}