Built-in Data Binding Converters

Avalonia UI includes a number of built-in data binding converters for common scenarios:

Converter	Description
Negation Operator	The ! operator can be placed in front of the data binding path to return the inversion of a Boolean value. See also the note below.
StringConverters.IsNullOrEmpty	Returns true if the input string is null or empty
StringConverters.IsNotNullOrEmpty	Returns false if the input string is null or empty
ObjectConverters.IsNull	Returns true if the input is null
ObjectConverters.IsNotNull	Returns false if the input is null
BoolConverters.And	A multi-value converter that returns true if all inputs are true.
BoolConverters.Or	A multi-value converter that returns true if any input is true.

Negation Operator Examples

This example shows the TextBlock when the bound value is false:

<StackPanel>
  <TextBox Name="input" IsEnabled="{Binding AllowInput}"/>
  <TextBlock IsVisible="{Binding !AllowInput}">Input is not allowed</TextBlock>
</StackPanel>

Negation also works when you bind to a non-Boolean value. This works because the bound value is first converted to a Boolean (using the function Convert.ToBoolean ) and then the result is negated.

For example, as the integer zero is converted to false (by the function Convert.ToBoolean) and all other integer values are converted to true, you can use the negation operator to show a message when a collection is empty, like this:

<Panel>
  <ListBox ItemsSource="{Binding Items}"/>
  <TextBlock IsVisible="{Binding !Items.Count}">No results found</TextBlock>
</Panel>

You can also use the negation operator twice. For example, where you want to perform the conversion from integer to Boolean, and then negate that value.

You can use this to hide a control when a collection is empty (count is zero), like this:

<Panel>
  <ListBox ItemsSource="{Binding Items}" IsVisible="{Binding !!Items.Count}"/>
</Panel>

Other Conversion Examples

This example binding will hide the text block if its bound text is null or empty:

<TextBlock Text="{Binding MyText}"
           IsVisible="{Binding MyText, 
                       Converter={x:Static StringConverters.IsNotNullOrEmpty}}"/>

And this example will hide the content control if the bound object is null or empty:

<ContentControl Content="{Binding MyContent}"
                IsVisible="{Binding MyContent, 
                            Converter={x:Static ObjectConverters.IsNotNull}}"/>

More Information

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You can follow the Avalonia UI value converter sample, here.