I was trying out some dummy application just to test binding modes. So, just curious to know how did the binding modes work. I have this xaml code-
<Button x:Name="btn"
Height="20"
Width="200"
VerticalAlignment="Top">
<Button.Style>
<Style TargetType="{x:Type Button}">
<Setter Property="IsEnabled"
Value="{Binding CanEnable, Mode=TwoWay}" />
<Style.Triggers>
<DataTrigger Binding="{Binding TextChanged}" Value="true">
<Setter Property="IsEnabled"
Value="true" />
</DataTrigger>
</Style.Triggers>
</Style>
</Button.Style>
</Button>
Here by button IsEanbled is binded to my viemodel property "CanEanble" whose default value is false. Now in my trigger i was listening to "TextChanged" property and setting button IsEnabled to true. Button gets enabled as it should be but the property "CanEnable" did not set to true even the biding mode is set to TwoWay..
Why this is happening??
By setting the value in the trigger you basically remove the binding you previously set in the style setter. Take a closer look at the style. You will notice that you basically you set the property IsEnabled twice. First in the style setter, second in the trigger. It is logical that the second value overrides the previous value.
The desired effect can be achieved from code if you set the value of the dependency property using SetCurrentValue method:
SetCurrentValue(Button.IsEnabledProperty, true);
This way the bindings set on this property will not be removed and it will work as expected.
Related
I want to show a StackPanel based on a particular condition. In this example I've used the BorderThickness property:
<ContentControl x:Name="gridDati" VirtualizingPanel.VirtualizationMode="Recycling" VirtualizingPanel.ScrollUnit="Item" HorizontalAlignment="Stretch" HorizontalContentAlignment="Stretch">
<ContentControl.Style>
<Style TargetType="ContentControl">
<Style.Triggers>
<DataTrigger Binding="{Binding Path=Items}" Value="{x:Null}">
<Setter Property="BorderThickness" Value="0" />
</DataTrigger>
<DataTrigger Binding="{Binding Path=Items.Count}" Value="0">
<Setter Property="BorderThickness" Value="12" />
</DataTrigger>
</Style.Triggers>
</Style>
</ContentControl.Style>
</ContentControl>
<StackPanel HorizontalAlignment="Center" VerticalAlignment="Center" x:Name="pnlLoading" Visibility="Visible">
<Label Content="">
<Label.Style>
<Style>
<Style.Triggers>
<DataTrigger Binding="{Binding Path=BorderThickness, ElementName=gridDati, UpdateSourceTrigger=PropertyChanged}" Value="0">
<Setter Property="TextBlock.Text" Value="" />
</DataTrigger>
<DataTrigger Binding="{Binding Path=BorderThickness, ElementName=gridDati, UpdateSourceTrigger=PropertyChanged}" Value="12">
<Setter Property="TextBlock.Text" Value="STAND BY" />
</DataTrigger>
</Style.Triggers>
</Style>
</Label.Style>
</Label>
</StackPanel>
Basically when in the code behind I apply a template on gridDati, while the item counter is still zero, the border is set correctly to 12. After that it turns to zero (item binded) and this behevior is what I want.
So, I also would like to show a StackPanel at the same condition, so I used a DataTrigger but seems that is not fired at all. How can I "link" these two condition? so show a stackpanel when I have items in the datagrid?
This is the proper way to declare the Label so you get the desired result.
<Label>
<Label.Style>
<Style TargetType="Label">
<Style.Triggers>
<DataTrigger Binding="{Binding Path=Items.Count}" Value="0">
<Setter Property="Content" Value="STAND BY"/>
</DataTrigger>
</Style.Triggers>
</Style>
</Label.Style>
</Label>
But there are a few points I need to explain to make sure you understand what I changed and why. I'm going to go through the XAML from the inside out.
First, I changed the Setter to use the right property name. You're using a Label, and your old Setter had Property="TextBlock.Text". TextBlock.Text is not a valid property name for a Label (no such property exists), so that wasn't going to work. The property you want is called Content.
Moving up one level to the DataTrigger. Instead of binding to gridDati that is binding to Items, I just bound directly to Items. You could do it the other way, but in my opinion it would be unusual and it might cause unforeseen bugs.
Next, you'll notice I removed the first DataTrigger. WPF dependency properties can be set in a number of different ways, and there is an order of precedence for which value will be taken over others. The default value (lowest precedence) for a Label's content is for it to be empty. When the DataTrigger applies the Setter, it overrides that value (it has higher precedence). When the DataTrigger condition is no longer fulfilled (Items.Count != 0), WPF stops applying the Setter and the value reverts back to the default, because there is no longer any value of higher precedence overriding it. So you don't need to add a second DataTrigger resetting to default, wit ill do that automatically.
Moving up further you'll see I changed the opening Style tag to <Style TargetType="Label">. It's common practice to set the TargetType of a Style. Doing this also gives you IntelliSense options for Setters in that Style, which might have helpped you catch the mistake you made by trying to use TextBlock.Text as a property name.
Finally, I removed Content="" from the opening Label tag. Setting the value of a property directly on an element in XAML has a very high precedence, which overrides all Styles and DataTriggers. As long as this was there, nothing you did in any Style would change anything for the Label's Content.
I'm trying to bind a button to a textbox's CanUndo property, except that I can't get it to work. I tried a direct binding like
IsEnabled="{Binding CanUndo, ElementName=txtDocument}"
But that didn't work. Button stayed disabled even after typing in textbox which would change the CanUndo property to true.
I also tried
<Button IsEnabled="False" >
<Button.Resources>
<Style TargetType="Button">
<Style.Triggers>
<DataTrigger Binding="{Binding CanUndo, ElementName=txtDocument}" Value="True">
<Setter Property="IsEnabled" Value="True" />
</DataTrigger>
</Style.Triggers>
</Style>
</Button.Resources>
<Image Source="/Images/32/undo.png" />
</Button>
I also tried with two separate datatriggers, one for enabled true and one for false, but still didn't work. Am I missing something fundamental? Like maybe this property doesn't raise the required events for binding changes?
Thanks
Set the Button's command property to the ApplicationCommands.Undo command and specify the CommandTarget property to be the TextBox.
The button will set the IsEnabled property based on ApplicationCommands.Undo command CanExecute state. The button will be disabled when CanExecute is false and enabled when CanExecute is true.
<StackPanel>
<TextBox x:Name="txtDocument">Test
</TextBox>
<Button Command="ApplicationCommands.Undo" CommandTarget="{Binding ElementName=txtDocument}" Content="Undo"/>
</StackPanel>
I have a ComboBox bound to a ViewModel property called Property.
Property is a TypeDescriptor.
When user changes the value in the ComboBox, the Property is updated.
On the UI i would like to either hide or make visible different controls: textbox, combobox, date picker etc.
Problem is, the DataTrigger is not working as expected.
<Style x:Key="textboxStyle"
TargetType="{x:Type TextBox}">
<Style.Triggers>
<DataTrigger Binding="{Binding Path=Property.PropertyType}"
Value="{x:Type Type={x:Type sys:String}}">
<Setter Property="Visibility"
Value="Visible" />
</DataTrigger>
</Style.Triggers>
</Style>
You might need to write a Converter which gets invoked when the value of 'Property' changes. The converter can be a 'TypeDescriptior to Visibility converter.
The reason why the above doesnt work is because 'PropertyType' doesnt trigger INotifyPropertyChanged.
I have a ComboBox, and i want to change its look when the ItemsSource property is null. When it is in that state, i want to show a TextPanel with the text "Retrieving data" in it, and give it a look kind of similar to the watermarked textbox.
I figure to do this i need a ControlTemplate, and a trigger. I have the ControlTemplate here:
<ControlTemplate x:Key="LoadingComboTemplate" TargetType="{x:Type ComboBox}">
<Grid>
<TextBlock x:Name="textBlock" Opacity="0.345" Text="Retrieving data..." Visibility="Hidden" />
</Grid>
<!--
<ControlTemplate.Triggers>
<Trigger Property="ComboBox.ItemsSource" Value="0">
<Setter Property="Visibility" Value="Visible" />
</Trigger>
</ControlTemplate.Triggers>
-->
</ControlTemplate>
but my issue is how do i set up the trigger to show this when the ItemsSource property is null? I have tried a couple of different ways, and each way has given me the error message "Value 'ItemsSource' cannot be assigned to property 'Property'. Invalid PropertyDescriptor value.". My ComboBox xaml is this (including the attempted trigger):
<ComboBox Margin="112,35,80,0"
Name="MyComboBox"
Height="22.723"
VerticalAlignment="Top"
DisplayMemberPath="FriendlyName"
SelectedValuePath="Path"
TabIndex="160"
>
<Trigger>
<Condition Property="ItemsSource" Value="0" />
<Setter Property="Template" Value="{StaticResource LoadingComboTemplate}" />
</Trigger>
</ComboBox>
now should the trigger go on the ComboBox, or on the ControlTemplate? How do i access the ComboBox's ItemsSource property? Should i even be using a trigger?
Thanks!
Try putting {x:Null} for the value of the condition instead of 0.
Also I got it working by moving the Trigger to a style and modifing it slightly, see below.
<Style TargetType="ComboBox" x:Key="LoadingComboStyle">
<Style.Triggers>
<Trigger Property="ItemsSource" Value="{x:Null}">
<Setter Property="Template" Value="{StaticResource LoadingComboTemplate}" />
</Trigger>
</Style.Triggers>
</Style>
<ComboBox Style="{StaticResource LoadingComboStyle}" .... >
The reason it only works in a style, is that only EventTriggers are allowed in the triggers collection directly on the Framework Element. For property triggers (like above) you need to use a style (I learn something every day).
See FrameworkElement.Triggers
Note that the collection of triggers established on an element only supports EventTrigger, not property triggers (Trigger). If you require property triggers, you must place these within a style or template and then assign that style or template to the element either directly through the Style property, or indirectly through an implicit style reference.
I have a checkbox in GridViewColumn which i use for show/change database value. The click event for the checkbox is used for change value in the database. For handling the state of property "IsChecked" I'm using datatrigger and a setter, se xaml code below:
<Style TargetType="CheckBox">
<Setter Property="IsEnabled" Value="True" />
<Style.Triggers>
<DataTrigger Binding="{Binding Path=ID, Converter={StaticResource Converter}}" Value="true">
<Setter Property="IsChecked" Value="True"/>
</DataTrigger>
</Style.Triggers>
</Style>
The binding works great until I click the checkbox. After I clicked the checkbox for the first time the state of the property "IsChecked" don't updates if a manually in the Database change the value which i mapped to the property "IsChecked".
If I map for example the same value to the property "Content" of the checkbox the trigger works fine even after I've clicked the checkbox.
Does anyone no whats the problem is?
Shouldn't
<Style TargetType="CheckBox">
instead be:
<Style TargetType="{x:Type CheckBox}">
Edit:
you could try this:
<Style TargetType="{x:Type CheckBox}" >
<Setter Property="IsChecked" Value="{Binding Path=ID, Converter={StaticResource Converter}}" />
</Style>
You can try to add a second data trigger to set the checkbox to false. As I can see from your code you set the IsChecked only to true, but never to false.
In stead of using Click to determine the changes, perhaps you can use the Checked and Unchecked events ?