接上篇, android自定義View&自定義ViewGroup(上) 上篇主要是自定義View，本篇來看看自定義ViewGroup。
先來複習一下一般自定義ViewGroup中需要複寫的方法：
void onMeasure(int widthMeasureSpec, int heightMeasureSpec)
void onSizeChanged(int w, int h, int oldw, int oldh)
void onLayout(boolean changed, int left, int top, int right, int bottom)
void onDraw(Canvas canvas)
複製程式碼注：ViewGroup的onLayout方法是必須重寫的，而onDraw方法預設是不會呼叫的，如果想執行onDraw方法，可以通過下面兩種方法： 1.設定透明背景： 在建構函式中：setBackgroundColor(Color.TRANSPARENT); 或者在xml中：android:background="@color/transparent" 2.或者可以在建構函式中新增setWillNotDraw(false); 自定義ViewGroup中如果需要獲得自定義屬性，方法和上篇自定義View中獲取方法是一樣的，請參照上篇。
###ViewGroup常用重寫方法:
- #####onMeasure measureChildren方法觸發所有子View的onMeasure方法測量自己並把測量結果回傳給ViewGroup(ViewGroup傳遞給子View建議寬高和測量模式，如果子View的寬高是wrap_content，那麼只有子View測量出自己的寬和高)，當所有子View測量完畢後，再呼叫setMeasuredDimension將ViewGroup自身的寬和高傳給它的父View。
- #####onSizeChanged 在onMeasure()後執行，只有大小發生了變化才會執行onSizeChange
- #####onLayout 排列所有子View的位置 通過getChildCount()獲取所有子view，getChildAt獲取childview呼叫各自的layout(int, int, int, int)方法來排列自己。
- #####onDraw 上面已經提到，自定義ViewGroup預設不會觸發onDraw方法，需要設定背景色或者setWillNotDraw(false)來手動觸發。
自定義ViewGroup例子，先上圖：
思路：首先是5個自定義圓環，在自定義ViewGroup的onLayout中排列他們，在onDraw中寫文字。 核心程式碼：
public class CustomFiveRings extends ViewGroup {
private Context mContext;
private TextPaint mPaint;
private int startX;//圓環起始X軸
private int startY;//圓環起始Y軸
private int mWidth;//ViewGroup的寬
private int mHeight;//ViewGroup的高
public CustomFiveRings(Context context) {
this(context, null);
}
public CustomFiveRings(Context context, AttributeSet attrs) {
this(context, attrs, 0);
}
public CustomFiveRings(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
setBackgroundColor(Color.TRANSPARENT);
mContext = context;
mPaint = new TextPaint();
mPaint.setAntiAlias(true);
mPaint.setDither(true);
mPaint.setTextSize(50);
mPaint.setColor(Color.BLACK);
}
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
//觸發所有子View的onMeasure函式去測量寬高
measureChildren(widthMeasureSpec, heightMeasureSpec);
//MeasureSpec封裝了父View傳遞給子View的佈局要求
int wMode = MeasureSpec.getMode(widthMeasureSpec);
int wSize = MeasureSpec.getSize(widthMeasureSpec);
int hMode = MeasureSpec.getMode(heightMeasureSpec);
int hSize = MeasureSpec.getSize(heightMeasureSpec);
switch (wMode) {
case MeasureSpec.EXACTLY:
mWidth = wSize;
break;
case MeasureSpec.AT_MOST:
//這裡應該先計算所有子view的寬度，暫時先寫死
mWidth = wSize;
break;
case MeasureSpec.UNSPECIFIED:
break;
}
switch (hMode) {
case MeasureSpec.EXACTLY:
mHeight = hSize;
break;
case MeasureSpec.AT_MOST:
//這裡應該先計算所有子view的高度，暫時先寫死
mHeight = hSize;
// mHeight = getCircleHeight() / 2 * 3;
break;
case MeasureSpec.UNSPECIFIED:
break;
}
setMeasuredDimension(mWidth, mHeight);
}
@Override
protected void onSizeChanged(int w, int h, int oldw, int oldh) {
super.onSizeChanged(w, h, oldw, oldh);
}
@Override
protected void onLayout(boolean changed, int l, int t, int r, int b) {
int childNum = getChildCount();
startX = startY = 0;
int gap = 10;//同一行圓圈之間的間隔
int screenWidth = DpUtil.getScreenSizeWidth(mContext);
int firstTotalWidth = 0;//第一行子View的總寬度
int secondTotalWidth = 0;//第二行子View的總寬度
for (int i = 0; i < childNum; i++) {
View childView = getChildAt(i);
int childWidth = childView.getMeasuredWidth();
if (i <= 2) {
//前三個總寬度
firstTotalWidth += childWidth;
} else {
//後兩個總寬度
secondTotalWidth += childWidth;
}
}
int leftFMargin = (screenWidth - firstTotalWidth - gap * 2) / 2;
int leftSMargin = (screenWidth - secondTotalWidth - gap) / 2;
for (int i = 0; i < childNum; i++) {
View childView = getChildAt(i);
int childWidth = childView.getMeasuredWidth();
int childHeight = childView.getMeasuredHeight();
if (i <= 2) {
//排列前三個圓圈
if (i == 0) {
childView.layout(leftFMargin + startX, startY, leftFMargin + startX + childWidth, startY + childHeight);
startX += childWidth;
} else {
childView.layout(leftFMargin + startX + gap, startY, leftFMargin + startX + gap + childWidth, startY + childHeight); startX += (childWidth + gap);
}
if (i == 2) {
startX = 0;
startY += childHeight / 2;
}
} else {
//排列後兩個圓圈
if (i == 3) {
childView.layout(leftSMargin + startX, startY, leftSMargin + startX + childWidth, startY + childHeight);
startX += childWidth;
} else {
childView.layout(leftSMargin + startX + gap, startY, leftSMargin + startX + gap + childWidth, startY + childHeight); startX += (childWidth + gap);
}
}
}
}
@Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
int screenWidth = DpUtil.getScreenSizeWidth(mContext);
String upStr = "同一個世界，同一個夢想";
String downStr = "One World,One Dream";
canvas.drawText(upStr, (screenWidth - mPaint.measureText(upStr)) / 2, getCircleHeight() / 2 * 3 + 60, mPaint);
canvas.drawText(downStr, (screenWidth - mPaint.measureText(downStr)) / 2, getCircleHeight() / 2 * 3 + 120, mPaint);
}
/**
* 獲得圓環高度
*
* @return 圓環高度
*/
private int getCircleHeight() {
//5個圓環大小是一樣的，這裡就直接取第一個了
View childView = getChildAt(0);
return childView.getMeasuredHeight();
}}
複製程式碼