自定义ViewGroup实现要点

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1. 核心方法重写

必须重写以下方法：

@Override
protected LayoutParams generateLayoutParams(LayoutParams p) {return new MarginLayoutParams(p);
}@Override
public LayoutParams generateLayoutParams(AttributeSet attrs) {return new MarginLayoutParams(getContext(), attrs);
}

2. onMeasure测量流程

关键操作：

1. 解析父容器测量规格
2. 测量所有子View
3. 计算自身最终尺寸

@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {// 获取测量模式和尺寸int widthMode = MeasureSpec.getMode(widthMeasureSpec);int heightMode = MeasureSpec.getMode(heightMeasureSpec);int sizeWidth = MeasureSpec.getSize(widthMeasureSpec);int sizeHeight = MeasureSpec.getSize(heightMeasureSpec);// 测量所有子ViewmeasureChildren(widthMeasureSpec, heightMeasureSpec);// 遍历子View计算尺寸int tWidth = 0, bWidth = 0;for (int i = 0; i < getChildCount(); i++) {View child = getChildAt(i);int cWidth = child.getMeasuredWidth();MarginLayoutParams params = (MarginLayoutParams) child.getLayoutParams();// 根据子View位置分组计算if (i == 0 || i == 1) {tWidth += cWidth + params.leftMargin + params.rightMargin;} else if (i == 2 || i == 3) {bWidth += cWidth + params.leftMargin + params.rightMargin;}}// 确定最终宽度int width = Math.max(tWidth, bWidth);setMeasuredDimension((widthMode == MeasureSpec.EXACTLY) ? sizeWidth : width,(heightMode == MeasureSpec.EXACTLY) ? sizeHeight : ...);
}

3. onLayout布局流程

关键步骤：

1. 获取子View尺寸
2. 计算每个子View坐标
3. 调用子View的layout()

@Override
protected void onLayout(boolean changed, int l, int t, int r, int b) {for (int i = 0; i < getChildCount(); i++) {View child = getChildAt(i);int cWidth = child.getMeasuredWidth();int cHeight = child.getMeasuredHeight();MarginLayoutParams params = (MarginLayoutParams) child.getLayoutParams();// 计算子View的四个边界坐标（示例）int cl = ... // 根据布局逻辑计算leftint ct = ... // 根据布局逻辑计算topint cr = cl + cWidth;int cb = ct + cHeight;child.layout(cl, ct, cr, cb);}
}

4. 实战技巧

• 测量模式处理：

  switch(widthMode) {case MeasureSpec.EXACTLY: // 精确值模式case MeasureSpec.AT_MOST: // 最大值模式case MeasureSpec.UNSPECIFIED: // 未指定模式
  }
  

• 边距处理：
  使用MarginLayoutParams获取子View的leftMargin/topMargin等值
• 性能优化：
  避免在onMeasure/onLayout中创建新对象，复用已有变量

5. 常见问题解决方案

子View重叠问题：

• 检查坐标计算逻辑是否考虑其他子View的位置
• 确保每次布局时重置定位坐标

测量不准确：

• 检查是否处理了wrap_content模式
• 验证子View测量是否调用measureChild()或measureChildren()

布局效率优化：

// 使用预计算减少循环内计算量
int currentX = 0, currentY = 0;
for (View child : children) {child.layout(currentX, currentY, currentX + childWidth, currentY + childHeight);currentX += childWidth + margin;
}