EvalExpression
| EvalExpression | |
|---|---|
| 220px | |
| imagecaption | |
| Name | EvalExpression |
| Namespace | UBIK.WinX.Controls |
| Purpose | Evaluate a C# expression in XAML |
| Version | 3.2+ |
Contents
Usage
The EvalExpression control allows to evaluate a C# expression from within XAML markup. The Expression has to be a single-line, valid C# expression ("Lambda") and has to return a single value; expressions can also reference names of subordinate EvalExpressionParameter items.
Examples
Simple Calculation
The following example shows how to use the control with three parameters, where the first two are user input (Textbox Param0 and Param1) and the third one is a property from its DataContext (ViewModel). The evaluated Result is then bound to a Textblock for output in the UI.
HorizontalAlignment="Center"
Orientation="Vertical">
<TextBox x:Name="Expression" Width="200" />
<TextBox x:Name="Param0" Width="200" />
<TextBox x:Name="Param1" Width="200" />
<ctrls:EvalExpression x:Name="Evaluator" Expression="{Binding ElementName=Expression, Path=Text}">
<ctrls:EvalExpressionParameter Name="P0" Value="{Binding ElementName=Param0, Path=Text, Converter={StaticResource ToType}, ConverterParameter='System.Int32'}" />
<ctrls:EvalExpressionParameter Name="P1" Value="{Binding ElementName=Param1, Path=Text, Converter={StaticResource ToType}, ConverterParameter='System.Int32'}" />
<ctrls:EvalExpressionParameter Name="P2" Value="{Binding IsLoggedIn}" />
</ctrls:EvalExpression>
<TextBlock Foreground="White" Text="{Binding ElementName=Evaluator, Path=Result}" />
</StackPanel>
Lets assume that the Textbox Param0 contains a text of 42 and Param1 contains a text of 43. If Expression now contains (P0 + P1) *2 then the result would display 170.
Setting a calculated Property Value
The following example shows how to create a button that adds and stores +5 to a numeric property value named MP_EXAMPLE, every time it is pressed:
<ctrls:EvalExpression x:Name="Evaluator" Expression=""MP_EXAMPLE|" + (P0 + 5)">
<ctrls:EvalExpressionParameter Name="P0" Value="{Binding Values[MP_EXAMPLE], Converter={StaticResource ToType}, ConverterParameter='System.Int32'}" />
</ctrls:EvalExpression>
<Button Content="Tap for 5 more" Command="{Binding SetPropertyValueAndValidateCommand}" CommandParameter="{Binding ElementName=Evaluator, Path=Result}"/>
</Grid>
Parameters
EvalExpressionParameters can be added as child objects to an EvalExpression control. Each parameter object needs a unique Name and a Value, where the latter can be either a constant or dynamic value supplied through a binding.
