浅谈WPF之控件拖拽与拖动

使用过office的visio软件画图的小伙伴都知道，画图软件分为两部分，左侧图形库，存放各种图标，右侧是一个画布，将左侧图形库的图标控件拖拽到右侧画布，就会生成一个新的控件，并且可以自由拖动。那如何在WPF程序中，实现类似的功能呢？今天就以一个简单的小例子，简述如何在WPF中实现控件的拖拽和拖动，仅供学习分享使用，如有不足之处，还请指正。

涉及知识点

WPF控件的拖拽与拖动，主要涉及知识点如下所示：

容器布局，本示例采用左右布局，主容器采用Grid并分成两列进行布局，左侧图标库采用UniformGrid布局，右侧画布采用Canvas布局。
控件拖拽，当图标库中的图标控件被鼠标按下时，通过调用 DragDrop.DoDragDrop方法实现拖拽功能，并且设置画布的AllowDrop属性为true，并触发拖拽松开事件。
控件拖动，当图标库中的图标拖拽到新画布容器后，就会生成一个新的控件，通过属性按下事件，鼠标移动事件，鼠标升起事件，来实现控件的拖动。

实现步骤

1. 页面布局

根据布局说明，页面分为左右两部分【Grid容器】，左侧图标库【UniformGrid】，右侧画布【Canvas】，如下所示：

<Window x:Class="DemoDragAndDrop.MainWindow"xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"xmlns:i="http://schemas.microsoft.com/xaml/behaviors"xmlns:d="http://schemas.microsoft.com/expression/blend/2008"xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"xmlns:local="clr-namespace:DemoDragAndDrop"mc:Ignorable="d"Title="MainWindow" Height="450" Width="800"><i:Interaction.Triggers><i:EventTrigger EventName="Loaded"><i:InvokeCommandAction Command="{Binding WinLoadedCommand}" CommandParameter="{Binding RelativeSource={RelativeSource Mode=FindAncestor, AncestorType=Window}}"/></i:EventTrigger></i:Interaction.Triggers><Grid><Grid.ColumnDefinitions><ColumnDefinition Width="Auto"></ColumnDefinition><ColumnDefinition Width="*"></ColumnDefinition></Grid.ColumnDefinitions><Border Grid.Column="0" BorderBrush="LightGray" BorderThickness="1"></Border><Border Grid.Column="1" BorderBrush="LightGray" BorderThickness="1"></Border><UniformGrid Grid.Column="0" Columns="2" VerticalAlignment="Top"><UniformGrid.Resources><Style TargetType="TextBlock"><Setter Property="Width" Value="100"></Setter><Setter Property="Height" Value="40"></Setter><Setter Property="FontSize" Value="18"></Setter><Setter Property="TextAlignment" Value="Center"></Setter><Setter Property="Padding" Value="10"></Setter><Setter Property="Margin" Value="5"></Setter><Setter Property="Background" Value="Blue"></Setter><Setter Property="FontWeight" Value="Bold"></Setter><Setter Property="Foreground" Value="White"></Setter></Style></UniformGrid.Resources><TextBlock Text="文本" Tag="Text"><i:Interaction.Triggers><i:EventTrigger EventName="MouseLeftButtonDown"><i:InvokeCommandAction Command="{Binding IconMouseLeftDownCommand}" CommandParameter="{Binding RelativeSource={RelativeSource Mode=FindAncestor, AncestorType=TextBlock}}"/></i:EventTrigger></i:Interaction.Triggers></TextBlock><TextBlock Text="按钮" Tag="Button"><i:Interaction.Triggers><i:EventTrigger EventName="MouseLeftButtonDown"><i:InvokeCommandAction Command="{Binding IconMouseLeftDownCommand}" CommandParameter="{Binding RelativeSource={RelativeSource Mode=FindAncestor, AncestorType=TextBlock}}"/></i:EventTrigger></i:Interaction.Triggers></TextBlock><TextBlock Text="单选按钮"></TextBlock><TextBlock Text="复选按钮"></TextBlock><TextBlock Text="圆形"></TextBlock><TextBlock Text="长方形"></TextBlock><TextBlock Text="直线"></TextBlock><TextBlock Text="三角形"></TextBlock></UniformGrid><Canvas x:Name="container" Grid.Column="1" AllowDrop="True" Background="White"><i:Interaction.Triggers><i:EventTrigger EventName="Drop"><i:InvokeCommandAction Command="{Binding CanvasDropCommand}" PassEventArgsToCommand="True"/></i:EventTrigger></i:Interaction.Triggers></Canvas></Grid>
</Window>

注意，在页面布局中，为图标库中的图标绑定了MouseLeftButtonDown事件命令，当鼠标左键按下时触发对应的事件，并开始拖拽。如下所示：

private ICommand  iconMouseLeftDownCommand;public ICommand IconMouseLeftDownCommand
{get {if (iconMouseLeftDownCommand == null){iconMouseLeftDownCommand = new RelayCommand<object>(IconMouseLeftDown);}return iconMouseLeftDownCommand; }
}private void IconMouseLeftDown(object sender)
{var tag = (sender as TextBlock)?.Tag?.ToString();if (tag == null){return;}var data = new DragDropData() { Tag = tag };//开启准备拖动操作DragDrop.DoDragDrop((DependencyObject)sender, data, DragDropEffects.Copy);
}

注意，在调用DragDrop.DoDragDrop方法开始拖拽时，此方法有三个参数【DoDragDrop(DependencyObject dragSource, object data, DragDropEffects allowedEffects)】，说明如下：

第一个参数是拖拽源控件。
第二个参数用于传递数据，可以传递参数，用于区分详细信息。
第三个参数是拖拽效果

在画布容器中松开拖拽的鼠标左键时，触发画布Drop事件，在此事件中创建新的控件，如下所示：

private ICommand canvasDropCommand;public ICommand CanvasDropCommand
{get {if (canvasDropCommand == null){canvasDropCommand = new RelayCommand<DragEventArgs>(CanvasDrop);}return canvasDropCommand; }
}private void CanvasDrop(DragEventArgs e)
{var data = e.Data.GetData(typeof(DragDropData)) as DragDropData;if (data != null){var position = e.GetPosition(this.containerCanvas);if (data.Tag == "Text"){//创建文本Border border = new Border();border.BorderThickness = new Thickness(1);border.BorderBrush = Brushes.Black;TextBlock text = new TextBlock(){Width = 120,Height = 30,Text = "文本1",FontSize = 14,Background = Brushes.LightGray,TextAlignment = TextAlignment.Center,Padding = new Thickness(5)};border.Child = text;border.MouseDown += Container_Control_MouseDown;border.MouseMove += Container_Control_MouseMove;border.MouseUp += Container_Control_MouseUp;this.containerCanvas.Children.Add(border);Canvas.SetLeft(border, position.X - 60);Canvas.SetTop(border, position.Y - 15);}if (data.Tag == "Button"){Button button = new Button(){Width = 120,Height = 30,Content = "按钮1",FontSize = 14,Background = Brushes.LightGray,HorizontalContentAlignment = HorizontalAlignment.Center,VerticalContentAlignment = VerticalAlignment.Center,Padding = new Thickness(5),BorderBrush = Brushes.Black,BorderThickness = new Thickness(1)};button.AddHandler(Button.MouseDownEvent,new MouseButtonEventHandler( Container_Control_MouseDown),true);button.AddHandler(Button.MouseMoveEvent, new MouseEventHandler(Container_Control_MouseMove), true);button.AddHandler(Button.MouseUpEvent, new MouseButtonEventHandler(Container_Control_MouseUp), true);this.containerCanvas.Children.Add(button);Canvas.SetLeft(button, position.X - 60);Canvas.SetTop(button, position.Y - 15);}}
}

注意：在此事件中，以下几点需要注意：

通过e.Data.GetData方法获取传递的参数。
通过e.GetPosition方法获取鼠标相对位置。参数是相对的对象，如Canvas容器等。
容器的Drop事件中，根据传递的内容创建控件对象，并为新创建的控件对象绑定MouseDown，MouseMove，MouseUp方法。其中Button按钮，由于鼠标按下事件和本省自带的Click事件相冲突，所以需要通过AddHandler方法添加鼠标事件。
通过Canvas.SetLeft，Canvas.SetTop方法设置控件对象在画布容器中的位置。

2. 控件拖动

在控件对象的MouseDown，MouseMove，MouseUp三个事件中，实现控件的拖动效果。即在MouseDown时开始，MouseMove中不断设置控件的Left，Top的值随鼠标而动，在MouseUp时停止。

private void Container_Control_MouseUp(object sender, MouseButtonEventArgs e)
{if(e.LeftButton== MouseButtonState.Released){Mouse.Capture(null);}
}private void Container_Control_MouseMove(object sender, MouseEventArgs e)
{if (e.LeftButton == MouseButtonState.Pressed){var position = e.GetPosition(this.containerCanvas);Canvas.SetLeft((UIElement)sender,position.X-60);Canvas.SetTop((UIElement)sender,position.Y-15);}
}private void Container_Control_MouseDown(object sender, MouseButtonEventArgs e)
{if(e.LeftButton ==MouseButtonState.Pressed){Mouse.Capture((IInputElement)sender);}
}

注意，启动Mouse.Capture功能是为了捕获鼠标的焦点，使其在鼠标移动期间一直保持焦点，防止鼠标与控件分离。