概述
本文描述了如何建立一個簡單的、自定義的用戶控件——一個平滑的進度條。
在早先的進度條控件版本中,例如在 Microsoft Windows Common Controls ActiveX 控件中提供的版本,您可以看到進度條有兩種不同的視圖。您可以通過設定 Scrolling 屬性來設定 Standard 視圖或是 Smooth 視圖。 Smooth 視圖提供了一個區域來平滑的顯示進度, Standard 試圖則看上去是由一個一個方塊來表示進度的。
在 Visual C# .NET 中提供的進度條控件只支持 Standard 視圖。
本文的代碼樣例揭示了如何建立一個有如下屬性的控件:
Minimum。該屬性表示了進度條的最小值。默認情況下是 0 ;您不能將該屬性設為負值。
Maximum。該屬性表示了進度條的最大值。默認情況下是 100 。
Value。該屬性表示了進度條的當前值。該值必須介於 Minimum 和 Maximum 之間。
ProgressBarColor。該屬性表示了進度條的顏色。
建立一個自定義的進度條控件
1、按著下面的步驟,在 Visual C# .NET 中建立一個 Windows Control Library 項目:
a、打開 Microsoft Visual Studio .NET。
b、點擊 File 菜單,點擊 New ,再點擊 Project 。
c、在 New Project 對話框中,在 Project Types 中選擇 Visual C# Projects,然後在 Templates 中選擇 Windows Control Library 。
d、在 Name 框中,填上 SmoothProgressBar ,並點擊 OK 。
e、在 Project Explorer 中,重命名缺省的 class module ,將 UserControl1.cs 改為 SmoothProgressBar.cs 。
f、在該 UserControl 對象的 Property 窗口中,將其 Name 屬性從 UserControl1 改為 SmoothProgressBar 。
2、此時,您已經從 control 類繼承了一個新類,並可以添加新的功能。但是,ProgressBar累是密封(sealed)的,不能再被繼承。因此,您必須從頭開始建立這個控件。
將下面的代碼添加到UserControl模塊中,就在“Windows Form Designer generated code”之後:
int min = 0; // Minimum value for progress range int max = 100; // Maximum value for progress range int val = 0; // Current progress Color BarColor = Color.Blue; // Color of progress meter protected override void OnResize(EventArgs e) { // Invalidate the control to get a repaint. this.Invalidate(); } protected override void OnPaint(PaintEventArgs e) { Graphics g = e.Graphics; SolidBrush brush = new SolidBrush(BarColor); float percent = (float)(val - min) / (float)(max - min); Rectangle rect = this.ClientRectangle; // Calculate area for drawing the progress. rect.Width = (int)((float)rect.Width * percent); // Draw the progress meter. g.FillRectangle(brush, rect); // Draw a three-dimensional border around the control. Draw3DBorder(g); // Clean up. brush.Dispose(); g.Dispose(); } public int Minimum { get { return min; } set { // Prevent a negative value. if (value < 0) { min = 0; } // Make sure that the minimum value is never set higher than the maximum value. if (value > max) { min = value; min = value; } // Ensure value is still in range if (val < min) { val = min; } // Invalidate the control to get a repaint. this.Invalidate(); } } public int Maximum { get { return max; } set { // Make sure that the maximum value is never set lower than the minimum value. if (value < min) { min = value; } max = value; // Make sure that value is still in range. if (val > max) { val = max; } // Invalidate the control to get a repaint. this.Invalidate(); } } public int Value { get { return val; } set { int oldValue = val; // Make sure that the value does not stray outside the valid range. if (value < min) { val = min; } else if (value > max) { val = max; } else { val = value; } // Invalidate only the changed area. float percent; Rectangle newValueRect = this.ClientRectangle; Rectangle oldValueRect = this.ClientRectangle; // Use a new value to calculate the rectangle for progress. percent = (float)(val - min) / (float)(max - min); newValueRect.Width = (int)((float)newValueRect.Width * percent); // Use an old value to calculate the rectangle for progress. percent = (float)(oldValue - min) / (float)(max - min); oldValueRect.Width = (int)((float)oldValueRect.Width * percent); Rectangle updateRect = new Rectangle(); // Find only the part of the screen that must be updated. if (newValueRect.Width > oldValueRect.Width) { updateRect.X = oldValueRect.Size.Width; updateRect.Width = newValueRect.Width - oldValueRect.Width; } else { updateRect.X = newValueRect.Size.Width; updateRect.Width = oldValueRect.Width - newValueRect.Width; } updateRect.Height = this.Height; // Invalidate the intersection region only. this.Invalidate(updateRect); } } public Color ProgressBarColor { get { return BarColor; } set { BarColor = value; // Invalidate the control to get a repaint. this.Invalidate(); } } private void Draw3DBorder(Graphics g) { int PenWidth = (int)Pens.White.Width; g.DrawLine(Pens.DarkGray, new Point(this.ClientRectangle.Left, this.ClientRectangle.Top), new Point(this.ClientRectangle.Width - PenWidth, this.ClientRectangle.Top)); g.DrawLine(Pens.DarkGray, new Point(this.ClientRectangle.Left, this.ClientRectangle.Top), new Point(this.ClientRectangle.Left, this.ClientRectangle.Height - PenWidth)); g.DrawLine(Pens.White, new Point(this.ClientRectangle.Left, this.ClientRectangle.Height - PenWidth), new Point(this.ClientRectangle.Width - PenWidth, this.ClientRectangle.Height - PenWidth)); g.DrawLine(Pens.White, new Point(this.ClientRectangle.Width - PenWidth, this.ClientRectangle.Top), new Point(this.ClientRectangle.Width - PenWidth, this.ClientRectangle.Height - PenWidth)); }