Difference between revisions of "EvalExpression"
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In this case, if the result of the P0 expression is zero or null, P1 will be effected. Otherwise, P2 will be. | In this case, if the result of the P0 expression is zero or null, P1 will be effected. Otherwise, P2 will be. | ||
<tab name="Xamarin"> | <tab name="Xamarin"> | ||
| + | <source lang = "xml"> | ||
<Controls:EvalExpression x:Name="WFcolors_Issued" Expression="(P0==0 || P0==null) ? P1 : P2"> | <Controls:EvalExpression x:Name="WFcolors_Issued" Expression="(P0==0 || P0==null) ? P1 : P2"> | ||
<Controls:EvalExpressionParameter Name="P0" Value="{Binding Values[SC_STATUS]}" /> | <Controls:EvalExpressionParameter Name="P0" Value="{Binding Values[SC_STATUS]}" /> | ||
| Line 106: | Line 107: | ||
<Controls:EvalExpressionParameter Name="P2" Value="{StaticResource MATAP_Priority_Green}" /> | <Controls:EvalExpressionParameter Name="P2" Value="{StaticResource MATAP_Priority_Green}" /> | ||
</Controls:EvalExpression> | </Controls:EvalExpression> | ||
| + | </source> | ||
| + | |||
</tab> | </tab> | ||
</tabs> | </tabs> | ||
Revision as of 13:53, 7 January 2021
| EvalExpression | |
|---|---|
| 220px | |
| imagecaption | |
| Name | EvalExpression |
| Namespace | "using:UBIK.WinX.Controls" in UBIK.UWP "clr-namespace:UBIK.CPL.Controls;assembly=UBIK.CPL" in UBIK.Xamarin |
| Purpose | Evaluate a C# expression in XAML |
| Version | 3.2+ in UBIK.UWP 1.0+ in UBIK.Xamarin |
Contents
Concept
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
 | When writing expressions in XAML code, you have to avoid (escape) special characters. There are useful online tools for this. |
Evaluation without parameters
UWP
The following example shows how to evaluate a simple expression without using any parameters and then use the result for visibility binding.
<ctrls:EvalExpression
x:Name="ExpressionEvaluator"
Context="{Binding Self}"
Expression="Context.Values["LK_OFFLINE"]!=null || Context.Values["GUIDREF"]!=null" />
<TextBlock Foreground="White" Visibility="{Binding ElementName=ExpressionEvaluator, Path=Result, Converter={StaticResource BoolToVisConverter}}" />
</StackPanel>
The TextBlock should be visible as long as at least one of the context object's two named properties has a value.
Xamarin
Simple Calculation
UWP
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.
Xamarin
Setting a calculated Property Value
UWP
The following example shows how to create a button that adds and stores +5 to the value of a a numeric property 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>
Xamarin
Conditional Statement
If / Or statements can be evaluated using the C# syntax P0 ? P1 : P2. In this case, if the result of the P0 expression is True, P1 will be effected. Otherwise, P2 will be.
UWP
<Controls:EvalExpressionParameter Name="P0" Value="{Binding StoredProfileParameters[WPType1]}" />
<Controls:EvalExpressionParameter Name="P1" Value="WPType1=1" />
<Controls:EvalExpressionParameter Name="P2" Value="{Binding ElementName=InitialiseParameter, Path=Result}" />
</Controls:EvalExpression>
If / Or statements are being evaluated using the C# syntax (P0==0 || P0==null) ? P1 : P2. In this case, if the result of the P0 expression is zero or null, P1 will be effected. Otherwise, P2 will be.
Xamarin
<Controls:EvalExpressionParameter Name="P0" Value="{Binding Values[SC_STATUS]}" />
<Controls:EvalExpressionParameter Name="P1" Value="LightGray" />
<Controls:EvalExpressionParameter Name="P2" Value="{StaticResource MATAP_Priority_Green}" />
</Controls:EvalExpression>
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.
