I have a collection databound to a ListBox. What I would like to do is show some UI based on whether or not some property of the member of the collection exists.
E.g.:
public class Widget
{
public string foo;
public string bar;
}
public ObservableCollection<Widget> Stuff;
XAML:
<ListBox ItemsSource="{Binding Stuff}">
<ListBox.ItemTemplate>
<DataTemplate>
<TextBlock Text="{Binding foo}"
Visiblity="{Binding
(foo != null ? Visibility.Visible : Visibility.Collapsed)
}"/>
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
Note the Visibility attribute on the TextBlock. Clearly this isn't supported, but it should give you an idea of what I want to do.
One possible solution is that I could add a property to widget that looks like this:
public Visibility has_foo;
And then:
... Visibility="{Binding has_foo}" ...
But it seems awkward to have to generate these additional properties.
I suspect there is a much better way. Is there? How would you do it?
Thanks.
Create a value converter. Something like
public class NullToVisibilityConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
return value != null ? Visibility.Visible : Visibility.Collapsed;
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
throw new NotImplementedException();
}
}
Then add it something like
<YourUserControl.Resources>
<NullToVisibilityConverter x:Key="NullToVisibilityConverter" />
</YourUserControl.Resources>
<ListBox ItemsSource="{Binding Stuff}">
<ListBox.ItemTemplate>
<DataTemplate>
<TextBlock Text="{Binding foo}"
Visiblity="{Binding foo,
Converter={StaticResource NullToVisibilityConverter}"/>
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
Obviously I've not implemented ConvertBack (not really sure if you will be able to convert back) but you shouldn't need it in this instance.
Related
I've a combobox, which allows me to select a type. When I select a type, i'm able to fill a component. But I'd like that my component corresponding to my type. So, if it's a date, i'd like to display a datepicker, and if it's a string, i'd like to display a textbox.
How can I do that ?
I don't want to change things around DataTemplate, because this row is a part of a datagrid :)
<DataGridTemplateColumn Header="SQLValue" Width="0.55*" CanUserResize="False" CanUserReorder="False">
<DataGridTemplateColumn.CellTemplate>
<DataTemplate>
<!-- HERE ! HOW CAN I CHOOSE ONE BY A CONDITION ? -->
<DatePicker/>
<TextBox Text="{Binding SqlValue, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"/>
</DataTemplate>
</DataGridTemplateColumn.CellTemplate>
</DataGridTemplateColumn>
The idea here is: you should a property in data context call DispType (int)
Then in each control you binding Visibility with above property, include a Converter convert number to Visible or not, Converter have parameter is number.
You can see my eg:
<Grid>
<Button Visibility="{Binding DispType, Converter={StaticResource VisibilityTypeConverter}, ConverterParameter=1}"/>
<TextBox Visibility="{Binding DispType, Converter={StaticResource VisibilityTypeConverter}, ConverterParameter=2}"/>
<DatePickerTextBox Visibility="{Binding DispType, Converter={StaticResource VisibilityTypeConverter}, ConverterParameter=3}"/>
</Grid>
You see the hard code for ConverterParameter.
And Converter class
public class VisibilityTypeConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
int actualType = parameter == null ? 0 : System.Convert.ToInt32(parameter);
int compareType = value == null ? 0 : System.Convert.ToInt32(value);
if (actualType == compareType)
{
return Visibility.Visible;
}
return Visibility.Collapsed;
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
throw new NotImplementedException();
}
}
Please not that code is only demo, you should change code to meet your expectation.
I would like to use static texts fetched from a web service in my WP7 app. Each text has a Name (the indetifier) and a Content property.
For example a text could look like this:
Name = "M43";
Content = "This is the text to be shown";
I would then like to pass the Name (i.e. the identifier) of the text to an IValueConverter, which would then look up the the Name and return the text.
I figured the converter to look something like this:
public class StaticTextConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
if (value != null)
{
return App.StaticTexts.Items.SingleOrDefault(t => t.Name.Equals(value)).Content;
}
return null;
}
}
Then in the XAML:
<phone:PhoneApplicationPage.Resources>
<Helpers:StaticTextConverter x:Name="StaticTextConverter" />
</phone:PhoneApplicationPage.Resources>
...
<TextBlock Text="{Binding 'M43', Converter={StaticResource StaticTextConverter}}"/>
However, this does not seem to work and I am not sure that I pass in the value to the converter correctly.
Does anyone have some suggestions?
I finally found the answer. The answer was a mix between that of #Shawn Kendrot and another question I asked here: IValueConverter not getting invoked in some scenarios
To summarize the solution for using the IValueConverter I have to bind my control in the following manor:
<phone:PhoneApplicationPage.Resources>
<Helpers:StaticTextConverter x:Name="TextConverter" />
</phone:PhoneApplicationPage.Resources>
<TextBlock Text="{Binding Converter={StaticResource TextConverter}, ConverterParameter=M62}" />
Since the ID of the text is passed in with the converter parameter, the converter looks almost the same:
public class StaticTextConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
if (parameter != null && parameter is string)
{
return App.StaticTexts.Items.SingleOrDefault(t => t.Name.Equals(parameter)).Content;
}
return null;
}
}
However, as it turns out, the binding and thus the converter is not invoked if it does not have a DataContext. To solve this, the DataContext property of the control just has to be set to something arbitrary:
<TextBlock DataContext="arbitrary"
Text="{Binding Converter={StaticResource TextConverter}, ConverterParameter=M62}" />
And then everything works as intended!
The problem lies in your binding. It will check the DataContext, and on this object, it will try to evaluate the properties M62 and ValueboxConsent on that object.
You might want to add static keys somewhere in your application where you can bind to:
<TextBlock Text="{Binding Source="{x:Static M62.ValueboxConsent}", Converter={StaticResource StaticTextConverter}}" />
Where M62 is a static class where your keys are located.. like so:
public static class M62
{
public static string ValueboxConsent
{
get { return "myValueBoxConsentKey"; }
}
}
If you want to use a value converter, you'll need to pass the string to the parameter of value converter
Xaml:
<TextBlock Text="{Binding Converter={StaticResource StaticTextConverter}, ConverterParameter=M43}"/>
Converter:
public class StaticTextConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
if (parameter != null)
{
return App.StaticTexts.Items.SingleOrDefault(t => t.Name.Equals(parameter)).Content;
}
return null;
}
}
xmlns:prop="clr-namespace:MyProj.Properties;assembly=namespace:MyProj"
<TextBlock Text="{Binding Source={x:Static prop:Resources.MyString}, Converter={StaticResource StringToUpperCaseConverter}}" />
I have the following converter defined (C#):
class BodyValueConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
string s = value.ToString();
int prefixLength;
if (!int.TryParse(parameter.ToString(), out prefixLength))
return s;
return s.Substring(0, prefixLength);
}
public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
throw new NotSupportedException();
}
}
This will start at the start of the string being passed and will return the amount of characters I specify as a parameter.
In my XAML I have instanced the converter:
<local:BodyValueConverter x:Key="BodyValueConverter"/>
In attempting to use this converter in a textblock I get an error:
<DataTemplate x:Key="AppointmentTemplate">
<StackPanel Orientation="Horizontal">
<TextBlock Text="{Binding Subject}"></TextBlock>
<TextBlock Text="{Binding Path=Subject, Converter={StaticResource BodyValueConverter}, ConverterParameter=1}"></TextBlock>
</StackPanel>
</DataTemplate>
The error is:
XAMLParseException: Provide value on 'System.Windows.Markup.StaticResourceHolder' threw an exception.
The first textblock works fine to display subject. The 2nd line is what gives me the exception.
What's the order of your objects in your XAML?
The Converter has to be defined prior to actually being used, so be sure your <Converter> is above your <DataTemplate> in your Resources
Another alternative is to switch to using a DynamicResource instead of a StaticResource, since a DynamicResource is evaluated when it is needed, not when the XAML is loaded
That error is usually thrown when it can't find the static resource you are looking for. You'll need to define that in your static resources.
<Window
.... snip ...
xmlns:local="clr-namespace:YourLocalNamespace"
<Window.Resources>
<local:BodyValueConverter x:Key="BodyValueConverter"/>
</Window.Resources>
.... snip ....
<DataTemplate x:Key="AppointmentTemplate">
<StackPanel Orientation="Horizontal">
<TextBlock Text="{Binding Subject}"></TextBlock>
<TextBlock Text="{Binding Path=Subject, Converter={StaticResource BodyValueConverter}, ConverterParameter=1}"></TextBlock>
</StackPanel>
</DataTemplate>
</Window>
Note: This is when you are defining it in Window. You could define it elsewhere.
If this isn't the issue.... to find a more detailed explanation of what the parse error is... check the inner exception text.
Is it possible to display this TextBlock, only if the Address.Length > 0 ? I'd like to do this directly into the xaml, I know I could put all my controls programmatically
<TextBlock Text="{Binding Path=Address}" />
Basically, you're going to need to write an IValueConverter so that you can bind the Visibility property of your TextBox to either the Address field, or a new field that you create.
If you bind to the Address field, here's how the binding might look like::
<TextBlock Text="{Binding Path=Address}"
Visibility="{Binding Path=Address, Converter={StaticResource StringLengthVisibilityConverter}}" />
And then StringLengthVisiblityConverter could look something like this:
public class StringLengthVisiblityConverter: IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
if (value == null || value.ToString().Length == 0)
{
return Visibility.Collapsed;
}
else
{
return Visibility.Visible;
}
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
// Don't need to implement this
}
}
Then you'd just need to add your converter as a resource, using syntax like this (where src is mapped to the namespace where the converter is defined):
<src:StringLengthVisiblityConverter x:Key="StringLengthVisiblityConverter" />
I would do this with another boolean property called HasAddress which returns Address.Length > 0.
<!-- In some resources section -->
<BooleanToVisibilityConverter x:Key="Bool2VisibilityConverter" />
<TextBlock
Text="{Binding Address}"
Visibility="{Binding HasAddress, Converter={StaticResource Bool2VisibilityConverter}}"
/>
You should also remember to notify the property change for HasAddress in the setter of Address.
You can create a StringToVisibility converter.
It will return Visibility.Visible if bound string is not null or empty and Visibility.Collapsed if it is.
Use this converter while binding Address with Visibility property of your TextBlock.
Example:
<TextBlock Text="{Binding Path=Address}" Visibility="{Binding Address, Converter={StaticResource StringToVisibilityConverter}}" />
I have two elements: a listbox and a "this list is empty" message. I'd like to bind their visibility to the list box's ItemsSource being empty. However, I'm not sure how to do this:
<TextBlock Text="No favorite searches yet. Add some by searching, then clicking 'Add to Favorites'"
Padding="10,0"
VerticalAlignment="Center"
Visibility="{Binding Path=FavoriteFilters.IsEmpty, Converter={StaticResource visibilityConverter}}"
/>
<ListBox ItemsSource="FavoriteFilters"
x:Name="favoriteFiltersList"
Visibility="{Binding Path=FavoriteFilters.IsEmpty, Converter={StaticResource visibilityConverter}}">
<ListBox.ItemTemplate>
<DataTemplate>
<my:FavoriteFilterLink />
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
They are both visible, although the ItemsSource is empty. Also, I'm not sure how to invert the condition for the ListBox.
The visibility converter:
public class VisibilityConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
if (value is bool?)
{
if (string.IsNullOrEmpty((string)parameter))
{
return (value as bool?).Value ? Visibility.Visible : Visibility.Collapsed;
} else
{
return (value as bool?).Value ? Visibility.Collapsed : Visibility.Visible;
}
}
throw new ArgumentException();
}
public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
throw new NotImplementedException();
}
}
You might be better off writing two converters, one for the ListBox the other for the TextBlock. The logic of each would be simpler and you wouldn't need to pass a parameter to get the correct result.
While it might not be as elegant as a single converter solution it will be far more maintainable.
If you really want to pass a parameter then you need to use the ConverterParameter.
There's an example here but I'm not 100% sure it'll meet your requirements. The simplified XAML syntax is:
<TextBlock Visibility="{Binding FavoriteFilters.IsEmpty,
Converter={StaticResource visibilityConverter}, ConverterParameter=false}"/>
<ListBox Visibility="{Binding FavoriteFilters.IsEmpty,
Converter={StaticResource visibilityConverter}, ConverterParameter=true}"/>
Then in your converter (simplified):
bool show = (bool)value;
bool visible = (bool)parameter;
if (visible)
{
return show ? Visibility.Visible : Visibility.Collapsed;
}
else
{
return show ? Visibility.Collapsed : Visibility.Visible;
}