我用C#做了一个屏保，代码如下，为什么我运行的时候按什么键都无法退出？

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace 屏保
{
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}

    private void label1_Click(object sender, EventArgs e)
    {

    }

    int deltX = 10;
    int deltY = 8;

    private void timer1_Tick(object sender, EventArgs e)
    {
        this.label1.Left += deltX;
        this.label1.Top += deltY;
        if (this.label1.Top < 0 ||
           this.label1.Top + this.label1.Height > this.Height)
            deltY = -deltY;
        if (this.label1.Left < 0 ||
            this.label1.Left + this.label1.Width > this.Width)
            deltX = -deltX;
    }
    private void Form1_KeyDown(object sender, System.Windows.Forms.KeyEventArgs e)
    {
        Application.Exit();
    }
}

}

窗体的keypreview设置为true