How to binding the DataContext of an user-control? - data-binding

Question

I have a user-control like this:
<UserControl x:Class="IPAddressWPFUserControl.IPAddressControl"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
mc:Ignorable="d" BorderThickness="0" OverridesDefaultStyle="False" BorderBrush="{x:Null}">
<Grid>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="auto" />
<ColumnDefinition Width="auto" />
<ColumnDefinition Width="auto" />
<ColumnDefinition Width="auto" />
<ColumnDefinition Width="auto" />
<ColumnDefinition Width="auto" />
<ColumnDefinition Width="auto" />
</Grid.ColumnDefinitions>
<TextBox Grid.Column="0" x:Name="txtboxFirstPart" TextChanged="txtbox_TextChanged" MaxLength="3" BorderThickness="0" TabIndex="1" PreviewKeyDown="txtboxFirstPart_PreviewKeyDown" PreviewKeyUp="txtboxFirstPart_PreviewKeyUp" Width="31" />
<Label Content="." Grid.Column="1" x:Name="label1" VerticalContentAlignment="Bottom" HorizontalAlignment="Left" Background="White" />
<TextBox Grid.Column="2" x:Name="txtboxSecondPart" MaxLength="3" TextChanged="txtbox_TextChanged" BorderThickness="0" TabIndex="2" KeyDown="txtboxSecondPart_KeyDown" PreviewKeyUp="txtboxSecondPart_PreviewKeyUp" Margin="0" HorizontalAlignment="Left" Width="31"/>
<Label Content="." Grid.Column="3" Grid.Row="0" x:Name="label2" VerticalContentAlignment="Bottom" HorizontalAlignment="Left" Background="White" />
<TextBox Grid.Column="4" x:Name="txtboxThridPart" MaxLength="3" TextChanged="txtbox_TextChanged" BorderThickness="0" TabIndex="3" VerticalContentAlignment="Bottom" KeyDown="txtboxThridPart_KeyDown" PreviewKeyUp="txtboxThridPart_PreviewKeyUp" Width="31" HorizontalContentAlignment="Center" />
<Label Content="." Grid.Column="5" x:Name="label3" VerticalContentAlignment="Bottom" HorizontalAlignment="Left" Background="White" />
<TextBox Grid.Column="6" x:Name="txtboxFourthPart" MaxLength="3" TextChanged="txtbox_TextChanged" BorderThickness="0" TabIndex="4" VerticalContentAlignment="Bottom" HorizontalAlignment="Left" Width="31" HorizontalContentAlignment="Center" />
</Grid>
Added Text property to it in the code behind:
public static readonly DependencyProperty TextProperty = DependencyProperty.Register("Text", typeof(string), typeof(IPAddressControl),
new PropertyMetadata("0.0.0.0", new PropertyChangedCallback(OnTextPropertyChanged)));
private static void OnTextPropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
IPAddressControl o = d as IPAddressControl;
try
{
var value = e.NewValue as string;
var splitValues = new string[4];
if (value != null)
{
var splits = value.Split(new char[] { '.' }, StringSplitOptions.None);
Array.Copy(splits, splitValues, splits.Length);
}
o.txtboxFirstPart.Text = splitValues[0];
o.txtboxSecondPart.Text = splitValues[1];
o.txtboxThridPart.Text = splitValues[2];
o.txtboxFourthPart.Text = splitValues[3];
}
catch (Exception ex)
{
throw new Exception("Error in IP control see inner exception!", ex);
}
o.RaiseTextChanged(e);
}
public string Text
{
get { return (string)this.GetValue(IPAddressControl.TextProperty); }
set { this.SetValue(IPAddressControl.TextProperty, value); }
}
public event DependencyPropertyChangedEventHandler TextChanged;
protected virtual void RaiseTextChanged(DependencyPropertyChangedEventArgs e)
{
if (this.TextChanged != null)
{
this.TextChanged(this, e);
}
}
When I am using it in the MainWindow like this:
<GroupBox Name="gb_Tcp" DataContext="{Binding TcpCollection}">
<my:IPAddressControl x:Name="tb_IpAddress" Text="{Binding Path=IpAddress, ElementName=gb_tcp}"/>
<TextBox x:Name="tb_Test" Text={Binding Path=IpAddress, ElementName=gb_tcp}" />
</GroupBox>
The problem is when I try to set the value in a button click event:
private void btn_IpReset_Click(object sender, RoutedEventArgs e)
{
tb_IpAddress.Text = source.IpAddress; //This failed to change
tb_Test.Text= source.IpAddress; //This changed successfully
}
I suppose this is because the user-control didn't change the datacontext to the MainWindow's? Or what could be the problem is? Thanks in advance!

Answer 1

It's because you didn't use a BindingMode that will update source like TwoWay or OneWayToSource. So, after tb_IpAddress.Text = source.IpAddress, the binding you have set will be overwrite by the local value. tb_Test.Text= source.IpAddress work because TextBox.Text's default binding mode is TwoWay.