WPF using ResizeGrip to resize controls

Question

I want that the user can resize a control by draging a resize-grip on the lower right border. With the ResizeGrip there seems to exists the perfect control for achieving this, but I don't see what is the plan to use this control. It does not derive from Thumb (however in msdn is written that it is an "implementation" of it), and does also not support the routed events of Thumb.

What is it correct usage of the ResizeGrip-control.

Update:

I've played around with ResizeGrip and I have experienced a lot of weird problems using it.

The most hard problem was that, using the ResizeGrip in a window that shows also a native ResizeGrip in the bottom right corner (ResizeMode="CanResizeWithGrip"), the window has begun to react really strange on mouse-input. In the end, I have disclaimed to use it. As a simple alternative, you can use the Thumb-control and attach it an appropriate Template.

Answer 1

Ok, I got bored last night and wrote a little sample for you using Thumb. You should be able to Copy/Paste/Compile/Run.

But basically, I created a UserControl named DialogReplica, just something that looks like a dialog with a grip, you can see it thrown in the main window.

<Window x:Class="ResizeGrip.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:ResizeGrip="clr-namespace:ResizeGrip"
    Title="MainWindow" Height="350" Width="525">
<Canvas>
    <ResizeGrip:DialogReplica Canvas.Top="25" Canvas.Left="100"/>
</Canvas>

Here's the xaml for the UserControl (you mostly interested in the Thumb part):

<UserControl x:Class="ResizeGrip.DialogReplica"
         xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
<Border x:Name="Border" HorizontalAlignment="Center" VerticalAlignment="Center" BorderBrush="#FF626161" BorderThickness="2" CornerRadius="3">

    <DockPanel x:Name="sizableContent" Background="LightGray" Focusable="False" LastChildFill="True" MinHeight="100" MinWidth="100">

        <Border DockPanel.Dock="Top" Background="Gray" Height="30">
            <DockPanel>
                <Button DockPanel.Dock="Right" Width="16" Height="16" 
                    VerticalAlignment="Center" HorizontalAlignment="Center"
                    VerticalContentAlignment="Top" HorizontalContentAlignment="Center"
                    Margin="0,0,4,0" Background="Transparent">
                    <Button.Content>
                        <Grid>
                            <Line X1="1" Y1="1" X2="8" Y2="8" Stroke="White" StrokeThickness="1"/>
                            <Line X1="1" Y1="8" X2="8" Y2="1" Stroke="White" StrokeThickness="1"/>
                        </Grid>
                    </Button.Content>
                </Button>
                <TextBlock Text="Pretend Dialog" Foreground="White" HorizontalAlignment="Center" VerticalAlignment="Center"/>
            </DockPanel>
        </Border>

        <DockPanel DockPanel.Dock="Bottom" HorizontalAlignment="Stretch">

            <Thumb DockPanel.Dock="Right" VerticalAlignment="Bottom" Margin="0,0,1,1"
                   DragDelta="OnResizeThumbDragDelta" 
                   DragStarted="OnResizeThumbDragStarted" 
                   DragCompleted="OnResizeThumbDragCompleted">
                <Thumb.Style>
                    <Style TargetType="{x:Type Thumb}" BasedOn="{x:Null}">
                        <Style.Setters>
                            <Setter Property="Template">
                                <Setter.Value>
                                    <ControlTemplate>
                                        <Grid x:Name="resizeVisual" DockPanel.Dock="Right" VerticalAlignment="Bottom"  >
                                            <Line X1="6" Y1="18" X2="18" Y2="6" Stroke="DarkGray" StrokeThickness="1.5"/>
                                            <!--smallest/right|bottom most -->
                                            <Line X1="10" Y1="18" X2="18" Y2="10" Stroke="DarkGray" StrokeThickness="1.5"/>
                                            <Line X1="14" Y1="18" X2="18" Y2="14" Stroke="DarkGray" StrokeThickness="1.5"/>
                                            <!--longers/left|top most-->
                                            <Grid.Style>
                                                <Style TargetType="{x:Type Grid}">
                                                    <Style.Triggers>
                                                        <Trigger Property="IsMouseOver" Value="True">
                                                            <Setter Property="Cursor" Value="SizeNWSE"/>
                                                        </Trigger>
                                                    </Style.Triggers>
                                                </Style>
                                            </Grid.Style>
                                        </Grid>
                                    </ControlTemplate>
                                </Setter.Value>
                            </Setter>
                        </Style.Setters>
                    </Style>
                </Thumb.Style>
            </Thumb>

            <StackPanel Orientation="Horizontal" HorizontalAlignment="Center">
                <Button Margin="12" Width="75" TabIndex="1" Content="Ok"/>
            </StackPanel>
        </DockPanel>

        <StackPanel HorizontalAlignment="Center" Margin="16,16,16,4">
            <TextBlock Text="Drag the lower right corner to resize."/>
        </StackPanel>
    </DockPanel>
</Border>

finally, here's the code behind for the UserControl

public partial class DialogReplica : UserControl
{
    private Cursor _cursor;

    public DialogReplica()
    {
        InitializeComponent();
    }

    private void OnResizeThumbDragStarted(object sender, DragStartedEventArgs e)
    {
        _cursor = Cursor;
        Cursor = Cursors.SizeNWSE;
    }

    private void OnResizeThumbDragCompleted(object sender, DragCompletedEventArgs e)
    {
        Cursor = _cursor;
    }

    private void OnResizeThumbDragDelta(object sender, DragDeltaEventArgs e)
    {
        double yAdjust = sizableContent.Height + e.VerticalChange;
        double xAdjust = sizableContent.Width + e.HorizontalChange;

        //make sure not to resize to negative width or heigth            
        xAdjust = (sizableContent.ActualWidth + xAdjust) > sizableContent.MinWidth ? xAdjust : sizableContent.MinWidth;
        yAdjust = (sizableContent.ActualHeight + yAdjust) > sizableContent.MinHeight ? yAdjust : sizableContent.MinHeight;

        sizableContent.Width = xAdjust;
        sizableContent.Height = yAdjust;
    }
}