Difference between revisions of "EvalExpression"
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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 [[EvalExpression#Parameters|EvalExpressionParameter]] items. | 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 [[EvalExpression#Parameters|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. | 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. | ||
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</StackPanel> | </StackPanel> | ||
</source> | </source> | ||
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Lets assume that the Textbox ''Param0'' contains a text of 42 and ''Param1'' contains a text of 43. If ''Expression'' now contains <code>(P0 + P1) *2</code> then the result would display 170. | Lets assume that the Textbox ''Param0'' contains a text of 42 and ''Param1'' contains a text of 43. If ''Expression'' now contains <code>(P0 + P1) *2</code> 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: | ||
| + | |||
| + | <source lang = "xml"> | ||
| + | <Grid xmlns:ctrls="using:UBIK.WinX.Controls"> | ||
| + | <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="Test" Command="{Binding SetPropertyValueAndValidateCommand}" CommandParameter="{Binding ElementName=Evaluator, Path=Result}"/> | ||
| + | </Grid> | ||
| + | </source> | ||
[[Category:Pages with broken file links|EvalExpression]] | [[Category:Pages with broken file links|EvalExpression]] | ||
Revision as of 12:28, 7 August 2019
| 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="Test" 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.
