WPF: How to reuse XAML Fragment? - wpf

Question

I want to reuse an XAML fragment with substitution strings as parameters.
sort of like a #define with some function style arguments.
Can I do this?
If so, how is the best way to go around doing it?
So, here's invalid XAML of what I want to do
<Template Base="TextBox" key="ValidatedTextBox">
<TextBox.Text>
<Binding NotifyOnValidationError="True" UpdateSourceTrigger="PropertyChanged" Path="{SomeAttributeName}">
<Binding.ValidationRules>
<local:SomeRule></local:SomeRule>
</Binding.ValidationRules>
</Binding>
</TextBox.Text>
</Template>
...
and then elsewhere in XAML, instead of using a TextBox, I'd do
<ValidatedTextBox SomeAttributeName="MyPropertyToBeBound" AttributeNotOnTemplate="Value">
<ElementNotOnTemplate />
</ValidatedTextBox>
In particular, I want to be able to customize instances of this template.
I'm happy to read docs, but I don't know what to search for to find appropriate docs that aren't hilariously complicated for essentially a find-and-replace mechanism.

Answer 1

I'm not sure whether you're just trying to add validation to a TextBox or create a custom control. If you're struggling with the validation this post gives a very nice overview. In summary, you can do something like this
public class ViewModel : System.ComponentModel.IDataErrorInfo
{
public ViewModel()
{
/* Set default age */
this.Age = 30;
}
public int Age { get; set; }
public string Error
{
get { return null; }
}
public string this[string columnName]
{
get
{
switch (columnName)
{
case "Age":
if (this.Age < 10 || this.Age > 100)
return "The age must be between 10 and 100";
break;
}
return string.Empty;
}
}
}
And then use it like this
<TextBox Text="{Binding Path=Age, UpdateSourceTrigger=PropertyChanged, ValidatesOnDataErrors=True}"/>
If you'd like to create your own error template you can do it for an individual TextBox like this
<TextBox Text="{Binding Age, UpdateSourceTrigger=PropertyChanged}">
<Validation.ErrorTemplate>
<ControlTemplate>
<StackPanel>
<!-- Placeholder for the TextBox itself -->
<AdornedElementPlaceholder x:Name="textBox"/>
<TextBlock Text="{Binding [0].ErrorContent}" Foreground="Red"/>
</StackPanel>
</ControlTemplate>
</Validation.ErrorTemplate>
</TextBox>
Alternatively, you can define a style like this
<Style TargetType="x:TextBox">
<Setter Property="Validation.ErrorTemplate">
<Setter.Value>
<ControlTemplate>
<StackPanel>
<AdornedElementPlaceholder/>
<TextBlock Text="{Binding [0].ErrorContent}" Foreground="Red"/>
</StackPanel>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
If you're trying to create a custom control this post and this question are worth looking at. The key part is adding a DependencyProperty to your control like this
public string Text
{
get { return (string)GetValue(TextProperty); }
set { SetValue(TextProperty, value); }
}
// Using a DependencyProperty as the backing store for Text. This enables animation, styling, binding, etc...
public static readonly DependencyProperty TextProperty =
DependencyProperty.Register("Text", typeof(string), typeof(MyTextBox), new PropertyMetadata(string.Empty, OnTextChangedCallback));
private static void OnTextChangedCallback(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
// Validation in here
}
Then you could use it like this
<MyTextBox Text="My Text" .../>