2017-06-25-自定义ViewGroup

自定义ViewGroup，一般分为四步走

1，继承自ViewGroup

public class CustomLayout extends ViewGroup {
    public CustomLayout(Context context, AttributeSet attr) {
    this(context, attr, 0);
}

    public CustomLayout(Context context, AttributeSet attr, int defStyle) {
    super(context, attr, defStyle);
    }
}

2，自定义的ViewGroup的属性-在value文件下的attrs.xml声明如下代码

<declare-styleable name="CustomLayout">
    <attr name="custom" format="integer" />
</declare-styleable>

然后在CustomLayout初始化的时候，获取自定义属性的值

TypedArray typedArray = context.obtainStyledAttributes(attrs, R.styleable.CustomLayout);
final int len = typedArray.getIndexCount();
for (int i = 0; i < len; i++) {
int styledAttr = typedArray.getIndex(i);
    switch (styledAttr) {
        case R.styleable.CustomLayout_custom:
            custom = typedArray.getInteger(i, 0);
            break;
        default:
            break;
    }
}

怎么使用这个自定义属性就不在此赘述了，相信大家都懂。。。

3，覆盖onMeasure方法，测量值+测量模式来确定ViewGroup的大小

@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
    final int len = getChildCount();
    final int width = MeasureSpec.getSize(widthMeasureSpec);
    int height = getPaddingTop();
    .....
    for (int i = 0; i < len; ++i) {
        View child = getChildAt(i);
        final ViewGroup.LayoutParams lp = child.getLayoutParams();
        int mode;
        if (lp.width > 0) {
            mode = MeasureSpec.EXACTLY;
        } else {
            if (lp.width == LayoutParams.MATCH_PARENT) {
                mode = MeasureSpec.EXACTLY;
            } else {
                mode = MeasureSpec.AT_MOST;
            }
        }
        final int childWidthSpec = MeasureSpec.makeMeasureSpec(numWidth, mode);
        final int childHeightSpec = MeasureSpec.makeMeasureSpec(0, MeasureSpec.UNSPECIFIED);
        
    }
    .....
    setMeasuredDimension(width, height + getPaddingBottom());
}

onMeasure的主要作用

• 确定子view的宽和高，

• 确定自己的宽和高。

• 根据子View 的布局文件，为子view设置测量模式和测量值
  测量 = 测量模式+测量值
  测量模式由三种：

  EXCTLY:指定大小
  
  AT_MOST:指定最大的大小
  
  UNSPCIFIED：不指定大小，要多大就是多大。一般用于ScroolView中

4，覆盖onLayout方法，指定每个子view的布局规则

@Override
protected void onLayout(boolean changed, int l, int t, int r, int b) {
    final int len = getChildCount();
    final int width = r - l;
    .....
    int maxRowHeight = 0;
    for (int i = 0; i < len; ++i) {
        View child = getChildAt(i);
        final int childWidth = child.getMeasuredWidth();
        final int childHeight = child.getMeasuredHeight();
        .....
        child.layout(left, top, left + childWidth, top + childHeight);
        .....
    }
}

这样就是自定义viewGroup的流程，具体的逻辑需要根据自身的业务逻辑来确定，因此这里的代码作为参考