如何在Bunifu UI文本框中设置或编码占位符/水印属性

嘿，我懂你遇到的困扰了——想用Bunifu TextBox做登录凭证输入框，却找不到自带的水印属性，之前给原生TextBox用的SetCueText还不管用。别慌，这里有几个靠谱的解决办法，适配不同版本的Bunifu UI：

方法1：用Bunifu自带的PlaceholderText属性（推荐） #

如果你的Bunifu UI是较新版本（比如Bunifu Framework v5+），其实已经内置了占位符功能，直接用就行，不用折腾API：

Private Sub Login_Load(sender As Object, e As EventArgs) Handles MyBase.Load
    Me.CenterToParent()
    ' 设置密码框的掩码
    BunifuTextbox2._TextBox.PasswordChar = "*"
    
    ' 直接给Bunifu TextBox设置占位符
    BunifuTextbox1.PlaceholderText = "Username"
    BunifuTextbox2.PlaceholderText = "Password"
End Sub

要是在属性面板里找不到PlaceholderText，记得检查你的Bunifu UI版本，更新到最新版就能看到这个属性了。

方法2：适配Bunifu的SetCueText API调用 #

如果你的Bunifu版本比较旧，没有内置占位符属性，那可以调整原生API的调用方式——因为Bunifu TextBox内部包裹了一个原生TextBox，得拿到它的句柄再发送消息：

Imports System.Runtime.InteropServices

Public Class Login
    ' 声明Windows API函数
    <DllImport("user32.dll", CharSet:=CharSet.Auto)>
    Private Shared Function SendMessage(hWnd As IntPtr, Msg As Integer, wParam As Integer, lParam As String) As IntPtr
    End Function

    ' 设置提示文本的消息常量
    Private Const EM_SETCUEBanner As Integer = &H1501

    ' 给Bunifu TextBox设置占位符的自定义方法
    Private Sub SetCueText(bunifuTb As Bunifu.Framework.UI.BunifuTextbox, cueText As String)
        ' 注意：有些版本的Bunifu TextBox内部控件叫TextBox而不是_TextBox，报错的话改一下
        SendMessage(bunifuTb._TextBox.Handle, EM_SETCUEBanner, 0, cueText)
    End Sub

    Private Sub Login_Load(sender As Object, e As EventArgs) Handles MyBase.Load
        Me.CenterToParent()
        BunifuTextbox2._TextBox.PasswordChar = "*"
        
        ' 调用自定义方法设置占位符
        SetCueText(BunifuTextbox1, "Username")
        SetCueText(BunifuTextbox2, "Password")
    End Sub

如果编译时提示_TextBox不可访问，那大概率是Bunifu版本的问题，把bunifuTb._TextBox改成bunifuTb.TextBox试试。

方法3：自定义绘制占位符（万能适配） #

要是上面两种方法都不适用，还可以自己在Paint事件里绘制占位符文本，完全可控：

Private Sub BunifuTextbox1_Paint(sender As Object, e As PaintEventArgs) Handles BunifuTextbox1.Paint
    Dim innerTb As TextBox = BunifuTextbox1._TextBox
    ' 只有输入框为空且未获得焦点时才绘制占位符
    If String.IsNullOrEmpty(innerTb.Text) AndAlso Not innerTb.Focused Then
        Using grayBrush As New SolidBrush(Color.Gray)
            ' 对齐输入框的内边距，让文本位置更自然
            e.Graphics.DrawString("Username", innerTb.Font, grayBrush, 
                New PointF(innerTb.Padding.Left, innerTb.Padding.Top))
        End Using
    End If
End Sub

' 焦点变化时触发重绘，显示/隐藏占位符
Private Sub BunifuTextbox1_Enter(sender As Object, e As EventArgs) Handles BunifuTextbox1.Enter
    BunifuTextbox1.Invalidate()
End Sub

Private Sub BunifuTextbox1_Leave(sender As Object, e As EventArgs) Handles BunifuTextbox1.Leave
    BunifuTextbox1.Invalidate()
End Sub

密码框的逻辑和这个一样，复制事件处理代码改一下控件名和占位符文本就行。

内容的提问来源于stack exchange，提问作者Lucifer Rodstark