Regular (not attached) properties in XAML can be assigned either as an attribute or as child element.
Example:
<TextBlock Foreground="Blue">Some text</TextBlock>
Or:
<TextBlock>
<TextBlock.Foreground>
<SolidColorBrush>Blue</SolidColorBrush>
</TextBlock.Foreground>
Some text
</TextBlock>
Since attached properties are usually simple, I only see examples of assigning to them using an attribute, example:
<TextBlock Grid.Row="1">Some text</TextBlock>
But is it possible to assign to an attached property using a child element?
I have a custom control that has an attached property of a complex (class) type. Since I can't specify the value in an attribute, I'm not sure how to assign to it from XAML.
This feature is called the property element syntax and yes, you can set attached properties using the element attribute syntax:
<TextBlock>
<Grid.Column>1</Grid.Column>
ABC
</TextBlock>
Related
in WPF one can bind to static properties. Now I know 2 ways of doing this:
Content="{x:Static stat:Statics.CurrentUser}"
Or:
Content="{Binding Source={x:Static stat:Statics.CurrentUser}}"
Are there any differences between these 2 methods?
Main difference in this case is that x:Static does not perform additional conversion
From x:Static Markup Extension
Use caution when you make x:Static references that are not directly the type of a property's value. In the XAML processing sequence, provided values from a markup extension do not invoke additional value conversion. This is true even if your x:Static reference creates a text string, and a value conversion for attribute values based on text string typically occurs either for that specific member or for any member values of the return type.
So lets say you do
<TextBlock Text="{x:Static SystemColors.ActiveBorderBrush}"/>
this will cause runtime error:
'#FFB4B4B4' is not a valid value for property 'Text'.
because SolidColorBrush is not String whilst
<TextBlock Text="{Binding Source={x:Static SystemColors.ActiveBorderBrush}}"/>
will work fine and display #FFB4B4B4 because it will perform ToString() conversion. Also without Binding you are not able to access instance properties of static object so for example you would not be able to get Color property of that brush
<TextBlock Text="{Binding Source={x:Static SystemColors.ActiveBorderBrush}, Path=Color}"/>
I create a datatemplate for a combobox as follows:
<DataTemplate x:Key="AircraftTypeTemplate">
<StackPanel Orientation="Horizontal" Width="340">
<ComboBox>
<ComboBoxItem>CJ1</ComboBoxItem>
<ComboBoxItem>CJ3</ComboBoxItem>
<ComboBoxItem>Bravo</ComboBoxItem>
<ComboBoxItem>Excel</ComboBoxItem>
<ComboBoxItem>Sovereign</ComboBoxItem>
</ComboBox>
</StackPanel>
</DataTemplate>
It renders fine, but I would like to be able to associate a value with each of the items without having to bind it to some data context. For example I would like the CJ1 comboboxitem to have a value of 5. How would I set those in XAML?
Like:
<ComboBoxItem Value="5">CJ1</ComboBoxItem>
Thanks!
You can set the Name property to be any arbitrary string and use that. For more flexibility, you can use the Tag property, which according to MSDN:
Gets or sets an arbitrary object value that can be used to store custom information about this object.
You can read more about Tag here. I'd say Tag is probably better as opposed to bending Name to your will, and you can stick a string into Tag just as easily as Name.
I'm trying to databind to a listbox like so:
<ListBox x:Name="MyListBox" Margin="0,0,0,65">
<ListBox.ItemTemplate>
<DataTemplate>
<TextBlock Text="{Binding Converter={StaticResource MyConverter}}" />
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
The reason I am binding to the whole object and not a property is because my converter will need multiple properties of the object to build the string that it returns.
This works and my string is returned. But then when I change the ObservableCollection that this is based on the value doesn't change on the screen. If I bind to just a single property and change it, then the value does change.
What can I do differently? I can't bind to a single property since I need the entire object in the converter... And the ConverterParameter is already being used.
Remember, if you bind to the "main" property and the value of the main property itself isn't changed, the binding will have no reason to refresh itself. It has no clue that your converter is actually based off of a sub-property. What you can do is use a MultiBinding where you bind not only the "main" property, but also a specific sub-property. This gives your IMultiValueConverter implementation access to the main data object, but because you're also binding to the sub-property that's changing, will also be refreshed when that sub-property's value changes.
You can try using a MultiBinding which I believe updates whenever any of its Bindings are triggered. You can also use an IMultiValueConverter or just take advantage of the StringFormat of the binding.
For example, I have a simple textbox bound to a property:
<TextBox Text="{Binding FirstName, Mode=TwoWay, ValidatesOnExceptions=True, NotifyOnValidationError=True}" />
The property looks something like this:
[Display(Name="Last Name")]
public string LastName { ... }
So, given the textbox, I would like to get the Display Name property from the attribute. This will be used in a composite control that includes a fieldlabel and some other niceties.
Thanks in advance.
I am not able to attempt this at the moment so this may not be accurate or even possible. As soon as I get to a computer that I can try this I will...until then, this is just theory.
I'm guessing in your composite control you'll have something like this for each data bound field:
<TextBlock Text="{Binding FirstName, Mode=OneWay}" />
<TextBox Text="{Binding FirstName, Mode=TwoWay, ...}" />
What you'll probably need to do in order to create a converter that will look at the binding data for the Display attribute, and convert the value to the attribute value instead. This would cause the above block to look like this:
<TextBlock Text="{Binding FirstName, Mode=OneWay, Converter={StaticResource AttributeConverter}, ConverterParameter=Display}" />
<TextBox Text="{Binding FirstName, Mode=TwoWay, ...}" />
Here I passed in the Display as the parameter in case you wanted to access a different attribute.
Again this is just theory since I'm not able to currently test this and cannot recall if IValueConverter.Convert(object value, ...) passes the object in question or just the string value in this case. If it's just the string value, it probably isn't possible, though if it's the object instead, it will depend on how much access you have to the reflection namespace to evaluate the attributes.
As soon as I am able to, I'll throw the scenario together and try it out.
EDIT:
For some reason the sytax highlighter is giving me the finger when I try to paste code in this edit
Anyways, after trying this out in a little project, it don't think you can do this.
Based on my suggestion of making 2 data bound controls and using a converter for the one that consumes the attribute, I did the following:
Created the xaml for the databound control.
Create the Custom Attribute for testing
Created the Model with the decorated property for testing.
Created the converter to attempt to read the attribute from the property.
Here's where I got caught up. I wasn't able to obtain the data bound type from the IValueConverter.Convert(...) method. The value parameter came through as String as did the targetType parameter. While that was the primary hangup, the second was that I was unable to dynamically identify the property name that the control was data bound to. This could be remedied through a converter parameter possibly.
Now, I WAS able to read the attribute value if I supplied the type of my test Model with the decorated property so that much is possible but I wasn't able to dynamically identify the type on the fly.
The only other way I can think of is create some form of observer or converter prior to the data truly being bound to your custom control.
Good Luck
Adding an x:Name attribute to a XAML element normally results in a member variable being added to the backing class that can then be accessed using normal code. When the element in question is part of the DataTemplate, the field does not get created.
I can sort of understand that the DataTemplate is making this a special case but can anyone explain the underlying principle to me? Also what are the options for getting access to the object within .NET Code?
<dataControls:DataForm x:Name="CompanyDetail" CurrentItem="{Binding CurrentItem}" AutoGenerateFields="False">
<dataControls:DataForm.EditTemplate>
<DataTemplate>
<StackPanel dataControls:DataField.IsFieldGroup="True">
<dataControls:DataField Label="About">
<Border Height="150" Style="{StaticResource HtmlPlaceHolderBorderStyle}" Width="298" VerticalAlignment="Top">
<telerik:RadHtmlPlaceholder x:Name="uxAboutHtml" x:FieldModifier="Public" HtmlSource="{Binding About, Mode=TwoWay}"/>
</Border>
</dataControls:DataField>
</StackPanel>
</DataTemplate>
</dataControls:DataForm.EditTemplate>
</dataControls:DataForm>
You can use the FrameworkElement.FindName("objectName") method on the parent of the DataTemplate e.g. var uxAboutHtml = CompanyDetail.FindName("uxAboutHtml"); to get a reference to the object. The downside to this is that paramater passed to FindName does not end up being strongly typed with the XAML x:Name"objectName" attribute.
I have changed tack on this and am now referencing the underlying object that the control is being bound to, which is probably a better way to go.
var htmlContent = (CompanyViewModel)CompanyDetail.CurrentItem;