设计模式-代理模式

创建具有现有对象的对象，以便向外界提供功能接口。用于解决直接访问对象时带来的问题

示例

interface IImage
{
    void Display();
}

public class RealImage : IImage
{
    private string fileName;
    public RealImage(string fileName)
    {
        this.fileName = fileName;
        LoadFromDisk(fileName);
    }
    public void Display()
    {
        //display
    }
    private void LoadFromDisk(string fileName)
    {
        //Load Image From Disk
    }
}

public class ProxyImage : IImage
{
    private RealImage realImage;
    private string fileName;
    public ProxyImage(string fileName)
    {
        this.fileName = fileName;
    }
    public void Display()
    {
        if(realImage == null)
            realImage = new RealImage(fileName);
        realImage.Diaplay();
    }
}

IImage image = new ProxyImage("test.jpg");
// 图像将从磁盘加载
image.display(); 
// 图像不需要从磁盘加载
image.display();