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1
定义函数时注意
void类型无返回值，可以对外界的变量进行操作
对于有返回值的变量尽量不要对外界的变量进行操作，因为后来可能会考虑多种情况（比如drawState = State.move;外界也在使用drawState，那么返回的结果是不确定的）
2
全局变量
尽量少定义全局变量，因为其他地方会不会使用到他
3
编写程序时要注意此处变量使用对其他位置的影响。
4 三个自定义函数
bool JudgingState(List<Shape> shapeList, int X, int Y) { var shape = JudgingShape(shapeList, X, Y); return shape == null ? false : true; } //功能函数，当鼠标在指定区域内，判断是哪个元素发生改变 Shape JudgingShape(List<Shape> shapeList, int X, int Y) { Shape shapeItem=null; foreach (Shape item in shapeList) { if (item != null) { if (item is Line) { double bianC = CountDistance(item.P1.X, item.P1.Y, item.P2.X, item.P2.Y); double bianA = CountDistance(item.P1.X, item.P1.Y, X, Y); double bianB = CountDistance(item.P2.X, item.P2.Y, X, Y); if (bianA + bianB < bianC + rongChaZhi) { shapeItem = item; break; } } else if (item is MyRectangle) { double bianC1 = CountDistance(item.P1.X, item.P1.Y, item.P2.X, item.P1.Y); double bianC2 = CountDistance(item.P2.X, item.P1.Y, item.P2.X, item.P2.Y); double bianC3 = CountDistance(item.P2.X, item.P2.Y, item.P1.X, item.P2.Y); double bianC4 = CountDistance(item.P1.X, item.P2.Y, item.P1.X, item.P1.Y); double bianC1A = CountDistance(X, Y, item.P1.X, item.P1.Y); double bianC1B = CountDistance(X, Y, item.P2.X, item.P1.Y); double bianC2A = CountDistance(X, Y, item.P2.X, item.P1.Y); double bianC2B = CountDistance(X, Y, item.P2.X, item.P2.Y); double bianC3A = CountDistance(X, Y, item.P2.X, item.P2.Y); double bianC3B = CountDistance(X, Y, item.P1.X, item.P2.Y); double bianC4A = CountDistance(X, Y, item.P1.X, item.P2.Y); double bianC4B = CountDistance(X, Y, item.P1.X, item.P1.Y); if (bianC1A + bianC1B < bianC1 + rongChaZhi || bianC2A + bianC2B < bianC2 + rongChaZhi || bianC3A + bianC3B < bianC3 + rongChaZhi || bianC4A + bianC4B < bianC4 + rongChaZhi) { shapeItem = item; break; } } else if (item is Ellipse) { } else { shapeItem = null; } } } return shapeItem; } //计算距离公式 private double CountDistance(double pAx, double pAy, double pBx, double pBy) { return Math.Sqrt(Math.Abs(pAx - pBx) * Math.Abs(pAx - pBx) + Math.Abs(pAy - pBy) * Math.Abs(pAy - pBy)); }
GDI绘图程序：
在paint函数中只进行绘画
在mouseDown,mouseMove，mouseUp进行各种状态的判断
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原文地址：http://www.cnblogs.com/lv-sally/p/4699994.html
