如何在btnGo_Click事件中触发.NET Label的Paint事件？

要在btnGo_Click事件中触发Label1的Paint事件，直接调用控件的重绘方法即可，WinForms提供了两种常用实现方式：

方法1：调用Invalidate() #

Invalidate()会标记Label1为需要重绘状态，系统会在合适时机自动触发Paint事件，适合无需立即重绘的场景：

Private Sub btnGo_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnGo.Click
    Label1.Invalidate()
End Sub

方法2：调用Refresh() #

Refresh()会立即强制控件完成重绘（等效于Invalidate() + Update()的组合操作），适合需要立刻看到重绘效果的场景：

Private Sub btnGo_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnGo.Click
    Label1.Refresh()
End Sub

额外优化提示 #

你的原代码在每次Paint事件触发时都从磁盘读取图片，会产生频繁IO操作影响性能，还可能引发资源泄漏问题。建议提前加载图片并缓存，示例如下：

Private img As Image

Private Sub Form1_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles MyBase.Load
    img = Image.FromFile("f:/myImage.bmp")
End Sub

Private Sub Label1_Paint(ByVal sender As Object, ByVal e As System.Windows.Forms.PaintEventArgs) Handles Label1.Paint
    Dim g As Graphics = e.Graphics
    g.DrawImage(img, New Point(0, 0))
End Sub

' 窗体关闭时释放图片资源
Private Sub Form1_FormClosed(ByVal sender As Object, ByVal e As System.Windows.Forms.FormClosedEventArgs) Handles Me.FormClosed
    img.Dispose()
End Sub

内容的提问来源于stack exchange，提问作者LaLue