VB中如何编写自己的进度条控件

简介

进度条控件是一个非常有用的控件，可以用来显示任务的进度。在VB中，可以使用内置的ProgressBar控件来实现这个功能。但是，ProgressBar控件的功能非常有限，只能显示一个简单的进度条。如果需要更复杂的进度条，如带百分比的进度条、带动画的进度条等，就需要自己编写一个进度条控件。

控件代码

Public Class ProgressBar

    Private _value As Integer = 0
    Private _maximum As Integer = 100
    Private _showPercentage As Boolean = True

    Public Sub New()

        Me.SetStyle(ControlStyles.UserPaint, True)

    End Sub

    Public Property Value As Integer
        Get
            Return _value
        End Get
        Set(ByVal value As Integer)
            If value < 0 Then
                _value = 0
            ElseIf value > _maximum Then
                _value = _maximum
            Else
                _value = value
            End If

            Me.Invalidate()

        End Set
    End Property

    Public Property Maximum As Integer
        Get
            Return _maximum
        End Get
        Set(ByVal value As Integer)
            If value < 1 Then
                _maximum = 1
            Else
                _maximum = value
            End If

            Me.Invalidate()

        End Set
    End Property

    Public Property ShowPercentage As Boolean
        Get
            Return _showPercentage
        End Get
        Set(ByVal value As Boolean)
            _showPercentage = value

            Me.Invalidate()

        End Set
    End Property

    Protected Overrides Sub OnPaint(ByVal e As PaintEventArgs)

        Dim g As Graphics = e.Graphics

        Dim width As Integer = Me.Width - 2
        Dim height As Integer = Me.Height - 2

        Dim percentage As String = String.Empty

        If _showPercentage Then
            percentage = String.Format("{0}%", Math.Round((_value / _maximum) * 100))
        End If

        g.FillRectangle(Brushes.LightGray, 1, 1, width, height)

        Dim progressWidth As Integer = Math.Round((_value / _maximum) * width)

        g.FillRectangle(Brushes.DarkBlue, 1, 1, progressWidth, height)

        g.DrawRectangle(Pens.Black, 0, 0, width, height)

        If _showPercentage Then
            g.DrawString(percentage, Me.Font, Brushes.Black, width / 2 - g.MeasureString(percentage, Me.Font).Width / 2, height / 2 - g.MeasureString(percentage, Me.Font).Height / 2)
        End If

    End Sub

End Class

使用控件

将控件添加到项目中后，即可在代码中使用它。例如，以下代码将创建一个进度条控件并将其添加到窗体中：

Dim progressBar As New ProgressBar()

progressBar.Location = New Point(10, 10)
progressBar.Size = New Size(200, 20)

Me.Controls.Add(progressBar)

然后，可以使用Value属性来设置进度条的值。例如，以下代码将进度条的值设置为50：

progressBar.Value = 50

结语

本文介绍了如何使用VB编写自己的进度条控件。该控件非常简单，但功能却非常强大，可以满足各种不同任务的需要。希望本文能对大家有所帮助。