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Difference between revisions of "EvalExpression"

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{{Hint|When writing expressions in XAML code, you have to avoid (escape) special characters. There are useful [https://www.freeformatter.com/xml-escape.html online tools] for this.}}
 
{{Hint|When writing expressions in XAML code, you have to avoid (escape) special characters. There are useful [https://www.freeformatter.com/xml-escape.html online tools] for this.}}
  
 +
==== Evaluation without parameters ====
 
<tabs>
 
<tabs>
 
<tab name="UWP">
 
<tab name="UWP">
−
 
−
==== Evaluation without parameters ====
 
 
The following example shows how to evaluate a simple expression without using any parameters and then use the result for visibility binding.
 
The following example shows how to evaluate a simple expression without using any parameters and then use the result for visibility binding.
−
 
 
<source lang = "xml">
 
<source lang = "xml">
 
<StackPanel xmlns:ctrls="using:UBIK.WinX.Controls">
 
<StackPanel xmlns:ctrls="using:UBIK.WinX.Controls">
Line 32: Line 30:
 
</StackPanel>
 
</StackPanel>
 
</source>
 
</source>
−
 
 
The TextBlock should be visible as long as at least one of the context object's two named properties has a value.
 
The TextBlock should be visible as long as at least one of the context object's two named properties has a value.
 +
</tab>
 +
 +
<tab name="Xamarin">
 +
</tab>
 +
</tabs>
  
 
==== Simple Calculation ====
 
==== Simple Calculation ====
 +
<tabs>
 +
<tab name="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.
 
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.
−
 
 
<source lang = "xml">
 
<source lang = "xml">
 
<StackPanel xmlns:ctrls="using:UBIK.WinX.Controls"
 
<StackPanel xmlns:ctrls="using:UBIK.WinX.Controls"
Line 53: Line 56:
 
</StackPanel>
 
</StackPanel>
 
</source>
 
</source>
−
 
 
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.
 +
</tab>
  
−
==== Setting a calculated Property Value ====
+
<tab name="Xamarin">
 +
{{Attention|Note that extra syntax is required to get the EvalExpression to work in Xamarin!}}
  
−
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:
+
<source lang = "xml">
 +
xmlns:controls="clr-namespace:UBIK.CPL.Controls;assembly=UBIK.CPL"
 +
...
 +
<controls:EvalExpression x:Name="UppercaseTitle" Expression="(P1.ToUpper())" Context="{Binding}">
 +
<controls:EvalExpressionParameter Name="P1" Value="{Binding PropertyItem.MetaProperty.Description}" />
 +
</controls:EvalExpression>
 +
</source>
  
 +
The above example converts a text (in this situation, the Description text of a property) to a capitalised version. Note that the text <b>Context="{Binding}"</b> is required for the expression to function in Xamarin.
 +
 +
To output the result of your expression, use the following syntax:
 +
<source lang = "xml">
 +
<Label Text="{Binding Path=Result, Source={x:Reference UppercaseTitle}}" />
 +
</source>
 +
Note that the correct way to reference elements in Xamarin is x:Reference (ie. the UWP equivalent of ElementName=), followed by the name given to your EvalExpression.
 +
</tab>
 +
</tabs>
 +
 +
==== Setting a calculated Property Value ====
 +
<tabs>
 +
<tab name="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:
 
<source lang = "xml">
 
<source lang = "xml">
 
<Grid xmlns:ctrls="using:UBIK.WinX.Controls">
 
<Grid xmlns:ctrls="using:UBIK.WinX.Controls">
Line 68: Line 92:
 
</Grid>
 
</Grid>
 
</source>
 
</source>
 +
</tab>
  
−
== Conditional Statement ==
+
<tab name="Xamarin">
 +
</tab>
 +
</tabs>
  
 +
== Conditional Statement ==
 
If / Or statements can be evaluated using the C# syntax P0 ? P1 : P2.  
 
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.
 
In this case, if the result of the P0 expression is True, P1 will be effected. Otherwise, P2 will be.
  
 +
<tabs>
 +
<tab name="UWP">
 
<source lang = "xml">
 
<source lang = "xml">
 
         <Controls:EvalExpression x:Name="InitialiseParameterWhenNull" Expression="(P0==null) ? P1 : P2">
 
         <Controls:EvalExpression x:Name="InitialiseParameterWhenNull" Expression="(P0==null) ? P1 : P2">
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         </Controls:EvalExpression>
 
         </Controls:EvalExpression>
 
</source>
 
</source>
 +
</tab>
  
 +
<tab name="Xamarin">
 +
</tab>
 +
</tabs>
  
 
== Parameters ==
 
== 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.
 
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.
−
 
+
<tabs>
 +
<tab name="UWP">
 
</tab>
 
</tab>
  
 
<tab name="Xamarin">
 
<tab name="Xamarin">
 +
</tab>
 +
</tabs>
 +
 
EvalExpressions are also available for usage with Xamarin customisations.  
 
EvalExpressions are also available for usage with Xamarin customisations.  
  
−
{{Attention|Note that extra syntax is required to get the EvalExpression to work in Xamarin!}}
 
  
−
<source lang = "xml">
 
−
xmlns:controls="clr-namespace:UBIK.CPL.Controls;assembly=UBIK.CPL"
 
−
...
 
−
<controls:EvalExpression x:Name="UppercaseTitle" Expression="(P1.ToUpper())" Context="{Binding}">
 
−
<controls:EvalExpressionParameter Name="P1" Value="{Binding PropertyItem.MetaProperty.Description}" />
 
−
</controls:EvalExpression>
 
−
</source>
 
  
−
The above example converts a text (in this situation, the Description text of a property) to a capitalised version. Note that the text <b>Context="{Binding}"</b> is required for the expression to function in Xamarin.
 
  
−
 
−
To output the result of your expression, use the following syntax:
 
−
<source lang = "xml">
 
−
<Label Text="{Binding Path=Result, Source={x:Reference UppercaseTitle}}" />
 
−
</source>
 
−
Note that the correct way to reference elements in Xamarin is x:Reference (ie. the UWP equivalent of ElementName=), followed by the name given to your EvalExpression.
 
−
 
−
</tab>
 
−
</tabs>
 
  
  

Revision as of 13:35, 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


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

IC Hint square.pngWhen 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.

<StackPanel xmlns:ctrls="using:UBIK.WinX.Controls">
        <ctrls:EvalExpression
               x:Name="ExpressionEvaluator"
               Context="{Binding Self}"
               Expression="Context.Values[&quot;LK_OFFLINE&quot;]!=null || Context.Values[&quot;GUIDREF&quot;]!=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.

<StackPanel xmlns:ctrls="using:UBIK.WinX.Controls"
        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

IC Attention.pngNote that extra syntax is required to get the EvalExpression to work in Xamarin!
xmlns:controls="clr-namespace:UBIK.CPL.Controls;assembly=UBIK.CPL"
...
<controls:EvalExpression x:Name="UppercaseTitle" Expression="(P1.ToUpper())" Context="{Binding}">
        <controls:EvalExpressionParameter Name="P1" Value="{Binding PropertyItem.MetaProperty.Description}" />
</controls:EvalExpression>

The above example converts a text (in this situation, the Description text of a property) to a capitalised version. Note that the text Context="{Binding}" is required for the expression to function in Xamarin.

To output the result of your expression, use the following syntax:

<Label Text="{Binding Path=Result, Source={x:Reference UppercaseTitle}}" />

Note that the correct way to reference elements in Xamarin is x:Reference (ie. the UWP equivalent of ElementName=), followed by the name given to your EvalExpression.

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:

<Grid xmlns:ctrls="using:UBIK.WinX.Controls">
    <ctrls:EvalExpression x:Name="Evaluator" Expression="&quot;MP_EXAMPLE|&quot; + (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:EvalExpression x:Name="InitialiseParameterWhenNull" Expression="(P0==null) ? P1 : P2">
            <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>

Xamarin

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.

UWP

Xamarin

EvalExpressions are also available for usage with Xamarin customisations.






See also

Retrieved from "https://wiki.augmensys.com/index.php?title=EvalExpression&oldid=22861"