我有一堂课:
public static class PictureBoxExtensions
{
public static Point ToCartesian(this PictureBox box, Point p)
{
return new Point(p.X, p.Y - box.Height);
}
public static Point FromCartesian(this PictureBox box, Point p)
{
return new Point(p.X, box.Height - p.Y);
}
}
我的问题是,与省略关键字相比,this
关键字前面PictureBox
的关键字有什么用?
扩展方法的调用类似于实例方法,但实际上是静态方法。实例指针“ this”是一个参数。
并且:您必须在要调用该方法的适当参数之前指定this-keyword。
public static class ExtensionMethods
{
public static string UppercaseFirstLetter(this string value)
{
// Uppercase the first letter in the string this extension is called on.
if (value.Length > 0)
{
char[] array = value.ToCharArray();
array[0] = char.ToUpper(array[0]);
return new string(array);
}
return value;
}
}
class Program
{
static void Main()
{
// Use the string extension method on this value.
string value = "dot net perls";
value = value.UppercaseFirstLetter(); // Called like an instance method.
Console.WriteLine(value);
}
}
有关更多信息,请参见http://www.dotnetperls.com/extension。
**编辑:尝试以下示例,并再次添加评论
pb.Location=pb.FromCartesian(new Point(20, 20));
查看结果**
using System;
using System.Drawing;
using System.Windows.Forms;
namespace WindowsFormsApplication1
{
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
private void Form1_Load(object sender, EventArgs e)
{
PictureBox pb = new PictureBox();
pb.Size = new Size(200, 200);
pb.BackColor = Color.Aqua;
pb.Location=pb.FromCartesian(new Point(20, 20));
Controls.Add(pb);
}
}
public static class PictureBoxExtensions
{
public static Point ToCartesian(this PictureBox box, Point p)
{
return new Point(p.X, p.Y - box.Height);
}
public static Point FromCartesian(this PictureBox box, Point p)
{
return new Point(p.X, box.Height - p.Y);
}
}
}
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