private static void 泛型接口的抗变()
{
IDisplay <Shape> shapeDisplay = new ShapeDisplay();
IDisplay <Rectangle> rectangleDisplay = shapeDisplay;
IIndex <Rectangle> rectangles = RectangleCollection.GetRectangles();
shapeDisplay.Show(rectangles[0]);
rectangleDisplay.Show(rectangles[0]);
}
private static void 泛型接口的协变()
{
IIndex <Rectangle> rectangles = RectangleCollection.GetRectangles();
//如果IIndex<out T> 去掉out IIndex<Shape> shapes = rectangles; 编译错误，
//Rectangle是Shape的子类 由子类泛型转换成基类泛型 需要协变（out T）？
//IIndex<out T> 约定返回类型只能是T 在具体实现类中IIndex<Rectangle> 返回类型只能是Rectangle
//Rectangle 是 Shape的子类 可以用父类的实例指向子类的引用进行编程
IIndex <Shape> shapes = rectangles;
for (int i = 0; i < shapes.Count; i++)
{
WriteLine(shapes[i]);
}
}
public void TestRectangleCollection()
{
// 协变
IIndex <Rectangle> rectangles = RectangleCollection.GetRectangles();
IIndex <Shape> shapes = rectangles;
for (int i = 0; i < shapes.Count; i++)
{
Debug.WriteLine(shapes[i]);
}
// 抗变
IDisplay <Shape> shapeDisplay = new ShapeDisplay();
IDisplay <Rectangle> rectangleDisplay = shapeDisplay;
Debug.WriteLine(rectangleDisplay.Show(rectangles[0]));
}
private DesignerGlyph GlyphFromPoint(Point point, out ActivityDesigner activityDesigner)
{
activityDesigner = null;
WorkflowView parentView = base.ParentView;
if (parentView != null)
{
RectangleCollection rectangles = new RectangleCollection();
foreach (ActivityDesigner designer in this.GetActivityDesigners(parentView.ClientRectangleToLogical(new Rectangle(Point.Empty, parentView.ViewPortSize))))
{
if (!rectangles.IsPointInsideAnyRectangle(point))
{
foreach (DesignerGlyph glyph in this.GetDesignerGlyphs(designer))
{
if (glyph.GetBounds(designer, false).Contains(point) && glyph.CanBeActivated)
{
activityDesigner = designer;
return glyph;
}
}
}
rectangles.AddRectangle(designer.Bounds);
}
}
return null;
}
