淺談WPF之控件拖拽與拖動

使用過office的visio軟件畫圖的小伙伴都知道，畫圖軟件分為兩部分，左側圖形庫，存放各種圖標，右側是一個畫布，將左側圖形庫的圖標控件拖拽到右側畫布，就會生成一個新的控件，并且可以自由拖動。那如何在WPF程序中，實現類似的功能呢？今天就以一個簡單的小例子，簡述如何在WPF中實現控件的拖拽和拖動，僅供學習分享使用，如有不足之處，還請指正。

涉及知識點

WPF控件的拖拽與拖動，主要涉及知識點如下所示：

容器布局，本示例采用左右布局，主容器采用Grid并分成兩列進行布局，左側圖標庫采用UniformGrid布局，右側畫布采用Canvas布局。
控件拖拽，當圖標庫中的圖標控件被鼠標按下時，通過調用 DragDrop.DoDragDrop方法實現拖拽功能，并且設置畫布的AllowDrop屬性為true，并觸發拖拽松開事件。
控件拖動，當圖標庫中的圖標拖拽到新畫布容器后，就會生成一個新的控件，通過屬性按下事件，鼠標移動事件，鼠標升起事件，來實現控件的拖動。

實現步驟

1. 頁面布局

根據布局說明，頁面分為左右兩部分【Grid容器】，左側圖標庫【UniformGrid】，右側畫布【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="按鈕" 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="單選按鈕"></TextBlock><TextBlock Text="復選按鈕"></TextBlock><TextBlock Text="圓形"></TextBlock><TextBlock Text="長方形"></TextBlock><TextBlock Text="直線"></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，在頁面布局中，為圖標庫中的圖標綁定了MouseLeftButtonDown事件命令，當鼠標左鍵按下時觸發對應的事件，并開始拖拽。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 };//開啟準備拖動操作DragDrop.DoDragDrop((DependencyObject)sender, data, DragDropEffects.Copy);
}

注意，在調用DragDrop.DoDragDrop方法開始拖拽時，此方法有三個參數【DoDragDrop(DependencyObject dragSource, object data, DragDropEffects allowedEffects)】，說明如下：

第一個參數是拖拽源控件。
第二個參數用于傳遞數據，可以傳遞參數，用于區分詳細信息。
第三個參數是拖拽效果

在畫布容器中松開拖拽的鼠標左鍵時，觸發畫布Drop事件，在此事件中創建新的控件，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"){//創建文本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 = "按鈕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，以下幾點需要注意：

通過e.Data.GetData方法獲取傳遞的參數。
通過e.GetPosition方法獲取鼠標相對位置。參數是相對的對象，如Canvas容器等。
容器的Drop事件中，根據傳遞的內容創建控件對象，并為新創建的控件對象綁定MouseDown，MouseMove，MouseUp方法。其中Button按鈕，由于鼠標按下事件和本省自帶的Click事件相沖突，所以需要通過AddHandler方法添加鼠標事件。
通過Canvas.SetLeft，Canvas.SetTop方法設置控件對象在畫布容器中的位置。

2. 控件拖動

在控件對象的MouseDown，MouseMove，MouseUp三個事件中，實現控件的拖動效果。即在MouseDown時開始，MouseMove中不斷設置控件的Left，Top的值隨鼠標而動，在MouseUp時停止。

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，啟動Mouse.Capture功能是為了捕獲鼠標的焦點，使其在鼠標移動期間一直保持焦點，防止鼠標與控件分離。