I have a grid with 2 columns, a listbox in column 0 and a number of other controls in the a secondary grid in the main grids column 1.
I want this controls only to be enabled (or perhaps visible) if an items is selected in the listbox through binding. I tried on a combo box:
IsEnabled="{Binding myList.SelectedIndex}"
But that does not seem to work.
Am I missing something? Should something like this work?
thanks
You'll need a ValueConverter for this. This article describes it in detail, but the summary is you need a public class that implements IValueConverter. In the Convert() method, you could do something like this:
if(!(value is int)) return false;
if(value == -1) return false;
return true;
Now, in your XAML, you need to do:
<Window.Resources>
<local:YourValueConverter x:Key="MyValueConverter">
</Window.Resources>
And finally, modify your binding to:
IsEnabled="{Binding myList.SelectedIndex, Converter={StaticResource MyValueConverter}"
Are you sure you didn't mean
IsEnabled="{Binding ElementName=myList, Path=SelectedIndex, Converter={StaticResource MyValueConverter}"
though? You can't implicitly put the element's name in the path (unless the Window itself is the DataContext, I guess). It might also be easier to bind to SelectedItem and check for not null, but that's really just preference.
Oh, and if you're not familiar with alternate xmlns declarations, up at the top of your Window, add
xmlns:local=
and VS will prompt you for the various possibilities. You need to find the one that matches the namespace you put the valueconverter you made in.
Copy-paste solution:
Add this class to your code:
public class HasSelectedItemConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
return value is int && ((int) value != -1);
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
throw new NotImplementedException();
}
}
Add converter as StaticResource to App.xml in <Application.Resources> section:
<local:HasSelectedItemConverter x:Key="HasSelectedItemConverter" />
And now you can use it in your XAML:
<Button IsEnabled="{Binding ElementName=listView1, Path=SelectedIndex,
Converter={StaticResource HasSelectedItemConverter}"/>
Hmm, perhaps it works with a BindingConverter, which converts explicitly all indexes > 0 to true.
Related
I have this listBox that gets populated, each item can be either male or female depending on the 'SEX' property that is binded to the listBox. (Could be either 'M' for male and 'F' for female)...
For each item i would like to display either a male or female symbol based on the list items SEX property.
for instance if "{Binding SEX}" equals 'M':
<Image Source="../Images/male48.png" Visibility="Visible" />
and if "{Binding SEX}" equals 'F':
<Image Source="../Images/female48.png" Visibility="Visible" />
How exactly would I go about getting this to work?
A common approach to this problem is to create a value converter, this converts the value returned by a binding into some other value that relates to the property of a UI control.
You can create a converter that takes the sex and maps it to an image source:
public class SexToSourceConverter : IValueConverter
{
public object Convert(object value, string typeName, object parameter, string language)
{
string url = ((string)value == "M") ? "../Images/male48.png" : "../Images/female48.png";
return new BitmapImage(new Uri(url , UriKind.Relative));
}
public object ConvertBack(object value, string typeName, object parameter, string language)
{
throw new NotImplementedException();
}
}
Using it in your XAML as follows:
<Image Source="{Binding Path=Sex, Converter={StaticResource SexToSourceConverter }" />
If someone is interested in how this could work, I've made a solution based on ColinE's answer. First, you've to create a new class which contain the conditions you'll like to add to the XAML code:
public class MyNiceConverterName : IValueConverter {
public object Convert(object value, Type targetType, object parameter, CultureInfo culture) {
// Your conditions here!
return value_you_want_to_return; // E.g., a string, an integer and so on
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture) {
throw new NotImplementedException(); // Leave this like here, don't worry
}
}
Call the class whatever you want (right now it's called MyNiceConverterName) and implement the Convert() method with the conditions you'd like to add to the XAML file. Remember to cast the object value to the type you're using (e.g., (int)value if it's an integer).
This is almost done! But not yet, first declare the converter in your XAML as a resource. You can paste this code below the namespaces declaration:
<Control.Resources>
<converter:MyNiceConverterName xmlns:converter="clr-namespace:My_Namespace" x:Key="MyNiceConverterName" />
</Control.Resources>
You've to declare the namespace where you defined the class (i.e., remove My_Namespace with yours') and also rename MyNiceConverterName to your class name. The key will be the name defined to reference the converter within the XAML document, here I've used the same class name but you can freely change it.
Finally, it's time to use the converter. Put this and you're done:
{Binding variable_with_value, Converter={StaticResource MyNiceConverterName}}
Remember to change variable_with_value with the one you'd like to use within your binding.
I hope it helps!
Either use a binding converter or use two triggers.
For Siverlight this is the correct IValueConverter link, I am not sure if triggers are supported.
I have 3 textblocks in a stackpanel in a DataTemplate.
the idea is that the format should be like "a b c" with spaces between the textblocks but it may happen that textblocks "a" and "b" might be empty, so i end up with something like this " c" ( two spaces before textblock c). How can i ensure that i have a margin but only if there is content?
If the TextBlock's Visibility is set to Collapsed, the Margin will not be shown. So I guess you can use a StringToVisibilityConverter to set its Visibility to Collapsed if the Text is empty.
Example
First you need to create a converter like this.
public class StringToVisibilityConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
if (value == null)
return Visibility.Collapsed;
if (value != null && string.IsNullOrWhiteSpace(value.ToString()))
return Visibility.Collapsed;
return Visibility.Visible;
}
public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
throw new NotImplementedException();
}
}
Then you need to include this converter into your xaml.
<converters:StringToVisibilityConverter x:Key="StringToVisibilityConverter " />
Finally, use it inside your TextBlock.
<TextBlock x:Name="MyTextBlock" Text="{Binding SomeText}"
Visibility="{Binding SomeText, Converter={StaticResource StringToVisibilityConverter}}" />
For more info regarding how to use a converter, please take a look at this post.
Hope it helps. :)
Add a converter to the Margin and bind it to the Text property. Have the converter sent the margin to a uniform thickness of 0 if the text content is blank.
Put the textblocks in a grid so that their locations are fixed. Add a converter to the martin and bind it to the text property, and if the length of that text is zero, then set the margin to zero.
I have a data source ('SampleAppearanceDefinitions'), which holds a single collection ('Definitions'). Each item in the collection has several properties, including Color, which is what I'm interested in here.
I want, in XAML, to display the Color of a particular item in the collection as text. I can do this just fine using this code below...
Text="{Binding Source={StaticResource SampleAppearanceDefinitions}, Path=Definitions[0].Color}"
The only problem is, this requires me to hard-code the index of the item in the Definitions collection (I've used 0 in the example above). What I want to do in fact is to get that value from a property in my current DataContext ('AppearanceID'). One might imagine the correct code to look like this....
Text="{Binding Source={StaticResource SampleAppearanceDefinitions}, Path=Definitions[{Binding AppearanceID}].Color}"
...but of course, this is wrong.
Can anyone tell me what the correct way to do this is? Is it possible in XAML only? It feels like it ought to be, but I can't work out or find how to do it.
Any help would be greatly appreciated!
Thanks!
AT
MultiBinding is your friend here:
Assuming you have a TextBlock:
<TextBlock>
<TextBlock.Text>
<MultiBinding Converter="{StaticResource AppearanceIDConverter}">
<Binding Source="{StaticResource SampleAppearanceDefinitions}" />
<Binding Path="AppearanceID" />
</MultiBinding>
</TextBlock.Text>
</TextBlock>
And define a MultiValueConverter to return what you wish to see:
public class AppearanceIDConverter : IMultiValueConverter
{
#region IMultiValueConverter Members
public object Convert(object[] values, System.Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
List<item> items = (List<item>)values[0]; //Assuming its items in a List
int id = (int)values[1]; //Assuming AppearanceID is an integer
return items.First(i => i.ID == id).Color; //Select your item based on the appearanceID.. I used LINQ, but a foreach will work just fine as well
}
public object[] ConvertBack(object value, System.Type[] targetTypes, object parameter, System.Globalization.CultureInfo culture)
{
throw new System.NotImplementedException();
}
#endregion
}
Of course, you will need to set the converter as a resource in your Resource dictionary, like you did SampleAppearanceDefinitions. You can also ditch the multibinding and use a regular binding to AppearanceID with a IValueConverter, if you can get to the SampleAppearanceDefinitions collection through code ;).
Hope this helps
Even if it could be possible you'd better not do that this way, but instead use a dedicated property in your view model or in the code behind of your view if it has only a pure graphical meaning.
This property, say "CurrentAppearance", would expose a Color property you could bind from your Xaml :
Text="{Binding CurrentAppearance.Color}"
which is more understandable.
As a general advice : avoid to spoil your Xaml with plumbing code : Xaml should be as readable as possible,
particularly if you work with a team of designers that have no coding skills and do not want to be concerned with the way you are managing the data.
Moreover, if later you decide to change the way data are managed you would not have to change your Xaml.
MultiBinding might actually work if your list is on a viewmodel instead of a staticresource. I was suprised myself to see that the object passed on to the view is actually a pointer to the object on the model, so changing the object in the view (eg. typing in new test in the textbox) directly affects the model object.
This worked for me. The ConvertBack method is never useed.
public class PropertyIdToPropertyConverter : IMultiValueConverter
{
public object Convert(object[] values, Type targetType, object parameter, CultureInfo culture)
{
if (values.Length == 2)
{
var properties = values[0] as ObservableCollection<PropertyModel>;
if (properties != null)
{
var id = (int)values[1];
return properties.Where(model => model.Id == id).FirstOrDefault();
}
}
return null;
}
public object[] ConvertBack(object value, Type[] targetTypes, object parameter, CultureInfo culture)
{
throw new NotImplementedException();
}
}
I want to do something like this:
<combobox x:Name="cboCustomers" ItemsSource="{Binding Path=Data.Customers}"/>
<combobox x:Name="cboInvoices"ItemsSource="{cboCustomers.SelectedItem.Invoices}"/>
Anyone know of a way to do something like this in Silverlight 3? I am sure there is some information about it out there, but I am having bad luck with Google in forming the question.
You need to specify ElementName on the second binding:
<combobox x:Name="cboCustomers" ItemsSource="{Binding Data.Customers}"/>
<combobox x:Name="cboInvoices"ItemsSource="{Binding SelectedItem.Invoices, ElementName=cboCustomers}"/>
If you also want the second combobox to be disabled until something has been selected in the first combobox you can bind the IsEnabled property of the second combobox to the SelectedItem property of the first combobox through a converter.
Add this class to your project:
public class NullToBooleanConverter : IValueConverter {
public Object Convert(Object value, Type targetType, Object parameter, CultureInfo culture) {
if (targetType == typeof(Boolean))
return value != null;
throw new NotSupportedException("Value converter can only convert to Boolean type.");
}
public Object ConvertBack(Object value, Type targetType, Object parameter, CultureInfo culture) {
throw new NotSupportedException("Value converter cannot convert back.");
}
}
Add an instance of this class to the resource dictionary of your user control (local is the namespace tag for the namespace of the converter):
<UserControl.Resources>
<local:NullToBooleanConverter x:Key="NullToBooleanConverter"/>
</UserControl.Resources>
Then you can add this to the second combobox:
IsEnabled="{Binding SelectedItem, ElementName=cboCustomers, Converter={StaticResource NullToBooleanConverter}}"
You'd be looking at a Cascading Combobox
http://weblogs.asp.net/manishdalal/archive/2008/10/22/cascading-combobox.aspx
In WPF, it seems to be impossible to select (with the mouse) a "null" value from a ComboBox. Edit To clarify, this is .NET 3.5 SP1.
Here's some code to show what I mean. First, the C# declarations:
public class Foo
{
public Bar Bar { get; set; }
}
public class Bar
{
public string Name { get; set; }
}
Next, my Window1 XAML:
<Window x:Class="WpfApplication1.Window1"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="Window1" Height="300" Width="300">
<StackPanel>
<ComboBox x:Name="bars"
DisplayMemberPath="Name"
Height="21"
SelectedItem="{Binding Bar}"
/>
</StackPanel>
</Window>
And lastly, my Window1 class:
public partial class Window1 : Window
{
public Window1()
{
InitializeComponent();
bars.ItemsSource = new ObservableCollection<Bar>
{
null,
new Bar { Name = "Hello" },
new Bar { Name = "World" }
};
this.DataContext = new Foo();
}
}
With me? I have a ComboBox whose items are bound to a list of Bar instances, one of which is null. I have bound the window to an instance of Foo, and the ComboBox is displaying the value of its Bar property.
When I run this app, the ComboBox starts with an empty display because Foo.Bar is null by default. That's fine. If I use the mouse to drop the ComboBox down and select the "Hello" item, that works too. But then if I try to re-select the empty item at the top of the list, the ComboBox closes and returns to its previous value of "Hello"!
Selecting the null value with the arrow keys works as expected, and setting it programatically works too. It's only selecting with a mouse that doesn't work.
I know an easy workaround is to have an instance of Bar that represents null and run it through an IValueConverter, but can someone explain why selecting null with the mouse doesn't work in WPF's ComboBox?
Well I recently ran into the same problem with null value for ComboBox.
I've solved it by using two converters:
For ItemsSource property: it replaces null values in the collection by any value passed inside converter's parameter:
class EnumerableNullReplaceConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
var collection = (IEnumerable)value;
return
collection
.Cast<object>()
.Select(x => x ?? parameter)
.ToArray();
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
throw new NotSupportedException();
}
}
For SelectedValue property: this one does the same but for the single value and in two ways:
class NullReplaceConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
return value ?? parameter;
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
return value.Equals(parameter) ? null : value;
}
}
Example of use:
<ComboBox
ItemsSource="{Binding MyValues, Converter={StaticResource EnumerableNullReplaceConverter}, ConverterParameter='(Empty)'}"
SelectedValue="{Binding SelectedMyValue, Converter={StaticResource NullReplaceConverter}, ConverterParameter='(Empty)'}"
/>
Result:
Note:
If you bind to ObservableCollection then you will lose change notifications. Also you don't want to have more than one null value in the collection.
The null "item" is not being selected by the keyboard at all - rather the previous item is being unselected and no subsequent item is (able to be) selected. This is why, after "selecting" the null item with the keyboard, you are thereafter unable to re-select the previously selected item ("Hello") - except via the mouse!
In short, you can neither select nor deselect a null item in a ComboBox. When you think you are doing so, you are rather deselecting or selecting the previous or a new item.
This can perhaps best be seen by adding a background to the items in the ComboBox. You will notice the colored background in the ComboBox when you select "Hello", but when you deselect it via the keyboard, the background color disappears. We know this is not the null item, because the null item actually has the background color when we drop the list down via the mouse!
The following XAML, modified from that in the original question, will put a LightBlue background behind the items so you can see this behavior.
<Window x:Class="WpfApplication1.Window1"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="Window1" Height="300" Width="300">
<StackPanel>
<ComboBox x:Name="bars" Height="21" SelectedItem="{Binding Bar}">
<ComboBox.ItemTemplate>
<DataTemplate>
<Grid Background="LightBlue" Width="200" Height="20">
<TextBlock Text="{Binding Name}" />
</Grid>
</DataTemplate>
</ComboBox.ItemTemplate>
</ComboBox>
</StackPanel>
</Window>
If you want further validation, you can handle the SelectionChanged event on the ComboBox and see that "selecting the null item" actually gives an empty array of AddedItems in its SelectionChangedEventArgs, and "deselecting the null item by selecting 'Hello' with the mouse" gives an empty array of RemovedItems.
I got a new solution for this question. "USING Mahapps"
xmlns:controls="http://metro.mahapps.com/winfx/xaml/controls"
<ComboBox x:Name="bars" **controls:TextBoxHelper.ClearTextButton="True"**
DisplayMemberPath="Name"
Height="21"
SelectedItem="{Binding Bar}"/>
You can use the close button to clear the content.
Thanks.
I know this answer isn't what you asked for (an explanation of why it doesn't work with the mouse), but I think the premise is flawed:
From my perspective as a programmer and user (not .NET), selecting a null value is a bad thing. "null" is supposed to be the absence of a value, not something you select.
If you need the ability explicitly not to select something, I would suggest either the work-around you mentioned ("-", "n.a." or "none" as a value), or better
wrap the combobox with a checkbox that can be unchecked to disable the combobox. This strikes me as the cleanest design both from a user's perspective and programmatically.
I spent one day to find a solution about this problem of selecting a null value in combobox and finally, yeah finally I found a solution in an article written at this url:
http://remyblok.tweakblogs.net/blog/7237/wpf-combo-box-with-empty-item-using-net-4-dynamic-objects.html
public class ComboBoxEmptyItemConverter : IValueConverter
{
/// <summary>
/// this object is the empty item in the combobox. A dynamic object that
/// returns null for all property request.
/// </summary>
private class EmptyItem : DynamicObject
{
public override bool TryGetMember(GetMemberBinder binder, out object result)
{
// just set the result to null and return true
result = null;
return true;
}
}
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
// assume that the value at least inherits from IEnumerable
// otherwise we cannot use it.
IEnumerable container = value as IEnumerable;
if (container != null)
{
// everything inherits from object, so we can safely create a generic IEnumerable
IEnumerable<object> genericContainer = container.OfType<object>();
// create an array with a single EmptyItem object that serves to show en empty line
IEnumerable<object> emptyItem = new object[] { new EmptyItem() };
// use Linq to concatenate the two enumerable
return emptyItem.Concat(genericContainer);
}
return value;
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
throw new NotImplementedException();
}
}
<ComboBox ItemsSource="{Binding TestObjectCollection, Converter={StaticResource ComboBoxEmptyItemConverter}}"
SelectedValue="{Binding SelectedID}"
SelectedValuePath="ID"
DisplayMemberPath="Name" />
this might not address your answer completely, but hopefully its a hit in the right direction:
Have you installed SP1?
From Scott Gu's Blog:
NET 3.5 SP1 includes several data binding and editing improvements to
WPF. These include:
StringFormat support within {{ Binding }} expressions to enable easy
formatting of bound values
New alternating rows support within controls derived
from ItemsControl, which makes
it easier to set alternating properties on rows (for example: alternating background colors)
Better handling and conversion support for null values
in editable controls Item-level
validation that applies validation rules to an entire bound item
MultiSelector support to handle multi-selection and bulk
editing scenarios
IEditableCollectionView support to interface data controls
to data sources and enable editing/adding/removing items in a transactional way
Performance improvements when binding to IEnumerable data
sources
Sorry if I wasted your time and this was not even close..but I think the problem is inherited from:
constraints of the strongly typed dataset
NullValueDataSet Explained here
But now the SP1 for .Net 3.5 should have addressed this issue..
I had the same kind of problem we did some work around like adding a value property to the collection item like this :
public class Bar
{
public string Name { get; set; }
public Bar Value
{
get { return String.IsNullOrEmpty(Name) ? null : this; } // you can define here your criteria for being null
}
}
Then while adding items instead of null I use the same object :
comboBox1.ItemsSource= new ObservableCollection<Bar>
{
new Bar(),
new Bar { Name = "Hello" },
new Bar { Name = "World" }
};
And instead of selecteditem I bind it to selectedvalue :
<ComboBox Height="23" Margin="25,40,133,0" DisplayMemberPath="Name"
SelectedValuePath="Value"
SelectedValue="{Binding Bar}"
Name="comboBox1" VerticalAlignment="Top" />
I know It is not a complete solution, just one workaround I use
Try Binding.FallbackValue
From 6 Things I Bet You Didn't Know About Data Binding in WPF
ComboBox needs a DataTemplate to display the item no matter how simple it is.
DataTemplate works like this: get a value from instance.[path], e.g.
bar1.Car.Color
So it cannot get a value from
null.Car.Color
It will throw a null reference exception. So, the null instance will not be displayed. But the the Color - if it is a reference type - is allowed to be null because there will be no exception in this case.
Just a guess, but I think it sounds reasonable.
Assume combobox is using "ListCollectionView" (lcv as its instance) as its item collection, which it should be.
If you are a programmer, what you gonna do?
I will respons to both Keyboard and Mouse.
Once I get Keyboard input, I use
lcv.MoveCurrentToNext();
or
lcv.MoveCurrentToPrevious();
So, sure keyboard works well.
Then I am working on respons Mouse inputs. And it comes the problem.
I want to listen 'MouseClick' event of my item. But probably, my Item doesn't generated, it is just a placeholder. So when user click on this placeholder, I get nothing.
If I get the event successfully, what's next. I will invoke
lcv.MoveCurrentTo(selectedItem);
the "selectedItem" which would be null is not an acceptable parameter here I think.
Anyway, it's just guessing. I don't have time to debug into it though I am able to. I have a bunch of defects to fix. Good Luck. :)