Vertically expand textbox automatically when text is too long

I am trying to mimic the Sticky Notes application in Windows 7. In the original application, if you type text into a Sticky Note and the text becomes too large (vertically, as in number of lines) to fit in the window, the window automatically expands vertically, one line at a time, to allow for more room. In other words, where in a normal Textbox a vertical scrollbar would appear and the text would scroll down (so that the first line becomes invisible), in the Sticky Notes the textbox expands exactly enough to fit the text so that no scrollbar appears. The scrollbar still appears when you manually resize the window afterwards, of course.

If you have Windows 7 just open the Sticky Notes application and type a few lines in the sticky note until it enlarges.

I am trying to mimic this effect but I'm having no luck. The problem seems that the actual Window should resize, not just the Textbox (I don't think WPF works this way, that a resize of a child element can开发者_如何学运维 'force' the parent element to become larger? At least not for a Window, right?).

The contents of the Window at this point are such:

<Window Background="Transparent" BorderBrush="Transparent"> 
    <!-- Transparent border to draw dropshadow on -->
    <Border Background="Transparent" BorderBrush="Transparent">
        <!-- Grid with UI elements -->
        <Grid Margin="5" Background="Transparent">
            <Grid.RowDefinitions>
                <RowDefinition Height="27" />       
                <RowDefinition Height="*" />
            </Grid.RowDefinitions> 

            <!-- Stickynote header -->
            <Border ... />

            <!-- Content -->
            <Border Grid.Row="1">

                <TextBox Text="{Binding ContentText}" ... />

            </Border>
        </Grid>
    </Border>
</Window>

Does anybody know how I can achieve this effect? Thanks!

---

Try the Window Property SizeToContent="Height"

Sample

<Window ...
        MaxHeight="500"
        SizeToContent="Height">
    <Border Background="Transparent" BorderBrush="Transparent">
        <Grid Margin="5" Background="Transparent">
            <Grid.RowDefinitions>
                <RowDefinition Height="27" />
                <RowDefinition Height="*" />
            </Grid.RowDefinitions>
            <Border Grid.Row="1">
                <TextBox AcceptsReturn="True" MinHeight="100"/>
            </Border>
        </Grid>
    </Border>
</Window>

---

Edit To use it with the TransparentWindow you posted, add transparentWindow.SizeToContent = SizeToContent.Manual in OnDragDelta (TransparentWindow.cs)

private static void OnDragDelta(object sender, DragDeltaEventArgs e)
{
    TransparentWindow transparentWindow = (TransparentWindow)sender;
    Thumb thumb = e.OriginalSource as Thumb;
    transparentWindow.SizeToContent = SizeToContent.Manual;
    if (thumb != null && transparentWindow.WindowState == WindowState.Normal)
    {
        //...
    }
}