在實際工作中，WPF提供的控制元件並不能完全滿足不同的設計需求。這時，需要我們設計自定義控制元件。

這裡LZ總結一些自己的思路，特性如下：

• Coupling
• UITemplate
• Behaviour
• Function Package

下面舉例說說在專案中我們經常用到調音臺音量條，寫一個自定義控制元件模擬調音臺音量條。

自定義控制元件SingnalLight,實現功能

• 接收來自外部的範圍0~100的數值
• 實時顯示接收數值
• 數值範圍0~50顯示綠色，50~85顯示黃色，85~100顯示紅色，沒有數值顯示褐色
• 可在父控制元件上拖拽該控制元件

public class SingnalLight : ContentControl {
        public int ValueA {
            get { return (int)GetValue(ValueAProperty); }
            set { SetValue(ValueAProperty, value); }
        }
    

        public SingnalLight() {
            this.AllowDrop = true;
        }


        
 
static SingnalLight() {
            DefaultStyleKeyProperty.OverrideMetadata(typeof(SingnalLight), new FrameworkPropertyMetadata(typeof(SingnalLight)));
        }


    }

ValueA為接受外部數值的屬性

2.複寫控制元件UITemplate

 1  <Style TargetType="{x:Type control:SingnalLight}">
 2         <Setter Property="RenderTransform">
 3             <Setter.Value>
 4                 <TranslateTransform X="{Binding Path=X,RelativeSource={RelativeSource AncestorType={x:Type control:SingnalLight}}}"
 5                                     Y="{Binding Path=Y,RelativeSource={RelativeSource AncestorType={x:Type control:SingnalLight}}}"/>
 6             </Setter.Value>
 7         </Setter>
 8         <Setter Property="Template">
 9             <Setter.Value>
10                 <ControlTemplate>
11                     <ControlTemplate.Resources>
12                         <control:SingnalLightStatusConverter x:Key="colorconverter"></control:SingnalLightStatusConverter>
13                         <control:SingnalLightValueConverter x:Key="valueconverter"></control:SingnalLightValueConverter>
14                     </ControlTemplate.Resources>
15                     <StackPanel>
16                         <TextBlock Text="{Binding Path=ValueA,RelativeSource={RelativeSource AncestorType={x:Type control:SingnalLight}}}"></TextBlock>
17                         <TextBlock Text="100"></TextBlock>
18                         <Border   
19                             x:Name="bd1"
20                             Height="{Binding Path=LightHeight,RelativeSource={RelativeSource AncestorType={x:Type control:SingnalLight}}}"
21                             SnapsToDevicePixels="True"
22                             BorderBrush="Black" BorderThickness="1" Background="Transparent">
23                             <Rectangle Fill="{Binding Path=ValueA,
24                                                       RelativeSource={RelativeSource AncestorType={x:Type control:SingnalLight}},
25                                                       Converter={StaticResource ResourceKey=colorconverter}}" 
26                                        VerticalAlignment="Bottom">
27                                 <Rectangle.Height>
28                                     <MultiBinding Converter="{StaticResource ResourceKey=valueconverter}">
29                                         <Binding Path="ValueA" RelativeSource="{RelativeSource AncestorType={x:Type control:SingnalLight}}"></Binding>
30                                         <Binding Path="Height" ElementName="bd1"></Binding>
31                                     </MultiBinding>
32                                 </Rectangle.Height>
33                             </Rectangle>
34                         </Border>
35                         <TextBlock Text="0"></TextBlock>
36                     </StackPanel>
37                 </ControlTemplate>
38             </Setter.Value>
39         </Setter>
40     </Style>

3.接受值判斷，SingnalLight通過實現IValueConverter和Override Arrange & Measure Methods，實現了UI呈現的繫結，

 1     public class SingnalLightStatusConverter : IValueConverter {
 2         public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture) {
 3             SolidColorBrush result = Brushes.Transparent;
 4             if (value.GetType() == typeof(int)) {
 5                 var color = System.Convert.ToInt32(value);
 6                 if (color < 50) result = Brushes.Green;
 7                 else if (color < 85 && color >= 50) result = Brushes.Yellow;
 8                 else if (color <= 100 && color >= 85) result = Brushes.Red;
 9                 else result = Brushes.Gray;
10             }
11             return result;
12         }
13 
14         public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture) {
15             throw new NotImplementedException();
16         }
17     }
18 
19     public class SingnalLightValueConverter : IMultiValueConverter {
20         public object Convert(object[] values, Type targetType, object parameter, System.Globalization.CultureInfo culture) {
21             double result = 0;
22             if (values[0].GetType() == typeof(int) && values[1].GetType() == typeof(double)) {
23                 result = (double)values[1] / 100 * System.Convert.ToDouble(values[0]);
24             }
25             return result;
26         }
27 
28         public object[] ConvertBack(object value, Type[] targetTypes, object parameter, System.Globalization.CultureInfo culture) {
29             throw new NotImplementedException();
30         }
31     }

1         protected override Size MeasureOverride(Size constraint) {
2             if (ActualHeight > 0) LightHeight = ActualHeight * .7;
3             return base.MeasureOverride(constraint);
4         }
5 
6         protected override Size ArrangeOverride(Size arrangeBounds) {
7             return base.ArrangeOverride(arrangeBounds);
8         }

4.控制元件支援拖拽，覆寫MouseDown,MouseMove,MouseUp方法。這樣寫的好處是，如果在父控制元件的事件中實現Drag，父控制元件如果有多個物件，這樣邏輯會十分混亂。

 1         protected override void OnMouseMove(MouseEventArgs e) {
 2             base.OnMouseMove(e);
 3             if (e.LeftButton == MouseButtonState.Pressed) {
 4                 _currentPoint = e.GetPosition(this);
 5                 X += _currentPoint.X - _startPoint.X;
 6                 Y += _currentPoint.Y - _startPoint.Y;
 7             }
 8         }
 9 
10         protected override void OnMouseDown(MouseButtonEventArgs e) {
11             base.OnMouseDown(e);
12             _startPoint = e.GetPosition(this);
13             this.CaptureMouse();
14         }
15 
16         protected override void OnMouseUp(MouseButtonEventArgs e) {
17             base.OnMouseUp(e);
18             this.ReleaseMouseCapture();
19         }

自定義控制元件系列博文連結：

WPF自定義控制元件（一）の控制元件分類 
WPF自定義控制元件（二）の重寫原生控制元件樣式模板
WPF自定義控制元件（三）の擴充套件控制元件 
WPF自定義控制元件（四）の自定義控制元件
WPF自定義控制元件（五）の使用者控制元件