I need to set background color of my controls, depending on a punch of ruler. So, I am trying to use converters to do that.
In my XAML:
<TextBox Background="{Binding Converter={StaticResource BackgroundConverter}, ConverterParameter='UserName'}">
In my converter I find for a rule for "UserName". But I use the entire binding object for that:
object IValueConverter.Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
if (value != null)
{
var person = (value as PersonBase).Person;
if (person.state == editing)
return GetRulesFor(parameter);
else
return Brushes.Silver;
It works in the first time screen is showing, but I need to update these properties when user edit form, cancel, etc.
How can I set my binding for this to happen ?
You can make a new property in the viewmodel and call it State, and return the person.state. When you change the state of the person object is changed just call OnPropertyChanged("State").
public class YourViewModel : INotifyPropertyChanged
{
// ... your code here
public StateObjectType State
{
get {return person.state;}
}
// when you modify the person state just call OnPropertyChanged("State")
}
In your view bind the textbox
<TextBox Background="{Binding State,Converter={StaticResource BackgroundConverter}, ConverterParameter='UserName'}">
This will make your code works.
Related
I have the an ICollectionView in my ViewModel:
public class ContactsPanelViewModel : ViewModelBase
{
private ICollectionView accountContactsView;
public ICollectionView AccountContactsView
{
get => accountContactsView;
set => NotifyPropertyChangedAndSet(ref accountContactsView, value);
}
public ContactsPanelViewModel()
{
AccountContactsView = CollectionViewSource.GetDefaultView(G.AccountContacts); //G.AccountContacts is an IEnumarable<Contact> object
AccountContactsView.SortDescriptions.Add(new SortDescription("FullName_LastNameFirst", ListSortDirection.Ascending));
AccountContactsView.CurrentChanged += NewContactSelected;
AccountContactsView.MoveCurrentToFirst();
}
}
This is the list it is bound to:
<ListView
x:Name="ContactList"
HorizontalAlignment="Left"
ItemsSource="{Binding Path=AccountContactsView, Converter={StaticResource ContactCardConverter}}"
IsSynchronizedWithCurrentItem="True"/>
And this is the converter I created:
public class ContactCardConverter : IValueConverter
{
public object Convert(object Value, Type TargetType, object Parameter, CultureInfo Culture)
{
if (Value is ListCollectionView)
{
List<ContactCard> contactCards = new List<ContactCard>(); //ContactCard is a UserControl
ListCollectionView data = Value as ListCollectionView;
if (data.Count > 0 && data.GetItemAt(0) is Contact)
{
foreach(Contact contact in data)
{
contactCards.Add(new ContactCard(contact));
}
return contactCards;
}
else
{
return null;
}
}
else
{
return null;
}
}
public object ConvertBack(object Value, Type TargetType, object Parameter, CultureInfo Culture)
{
if (Value is ContactCard)
{
return (Value as ContactCard).Contact;
}
else
{
return null;
}
}
}
The issue is that because I am using a converter the CurrentItem in my ICollectionView isn't being synchronized when the ListView selection changes. The converter is definitely the issue since removing the converter makes it work perfectly.
I added in a ConvertBack function thinking it would call that if there was a converter used but it didn't work.
I could theoretically make the ICollectionView of the type ContactCard (which is a UserControl), but that doesn't seem like it is how it should be done since from what I understand the ViewModel shouldn't be dependent on how the View will look. This would also add some complecity as I would need to keep the ICollectionView in sync with my actual collection of Contact objects.
What is the proper way to synchronize a ListView and an ICollectionView when the ListView uses a converter?
The proper way is don't use a converter.
You shouldn't convert your viewmodel-CollectionView to the List(as in your case) or another CollectionView in converter, because otherwise in case you created a CollectionView in converter you will synchronize your view (and IsSynchronizedWithCurrentItem works good) against in converter created collection. List can't be synchronized, because it does not implement IColectionView and has not CurrentItem.
The proper way is don't use a converter and put ContactCard-UserControl to the ListView.ItemTemplate.
<ListView.ItemTemplate>
<DataTemplate>
<youCustomCtlNameSpace:ContactCard Contact="{Binding}"/>
</DataTemplate>
</ListView.ItemTemplate>
If you mandatory wants to use a converter, then IsSynchronizedWithCurrentItem makes no sense and you have to synchronize V and VM by yourself via binding with converter to ListView.SelectedItem and your Contact have to hold reference to the UI-object(It's MVVM conform, if you have no dependencies to View see: Is MVVM pattern broken?). But as I already noted it's not a preferred way!
I am planning to implement code that will use an IValueConverter to display units of measurement in either metric or imperial based on a boolean the user sets. The issue I am facing is that the data stored in my database is required to always be in metric. I'm using Entity Framework database first if that makes a difference.
So the situation I am wondering about is this: if a user has chosen to display data in imperial units, but then alters one of the fields, and saves it - how do I ensure that it is saved properly in metric? From what I've gathered by researching online it looks like that would be part of the converter's ConvertBack method? Right now I call Textbox.GetBindingExpression(TextBox.TextProperty).UpdateSource(); to save the data, and I don't understand how to make that work since, as I understand, it just grabs the value in the TextBox and saves it. Am I right, or if there is a ConvertBack method will that be called in order to get the TextProperty?
Also, generally speaking, am I going about this the correct way (i.e. using an IValueConverter to alter the display)? To be honest I am in way over my head on this project, but I have deadlines fast approaching, and have a dire need to do this right. Any help would be greatly appreciated.
Thanks.
So you have some model, and you want to edit some properties of that model using TextBox and ValueConverter. Let's take some dummy value converter, which will multiply value by 10, and in ConvertBack will divide value by 10
public class MyConverter : IValueConverter {
public object Convert(object value, Type targetType, object parameter, CultureInfo culture) {
if (value == null || value == DependencyProperty.UnsetValue)
return null;
return (decimal) value*10;
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture) {
if (value == null || value == DependencyProperty.UnsetValue)
return 0;
decimal d;
if (decimal.TryParse((string) value, out d))
return d/10;
return 0;
}
}
Now some test model
public class MyModel : INotifyPropertyChanged {
private decimal _someValue;
public decimal SomeValue
{
get { return _someValue; }
set
{
if (value == _someValue) return;
_someValue = value;
OnPropertyChanged();
}
}
public event PropertyChangedEventHandler PropertyChanged;
[NotifyPropertyChangedInvocator]
protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null) {
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
}
}
And then you have your textbox
<TextBox Width="150" Height="20" Text="{Binding SomeValue, Mode=TwoWay, Converter={StaticResource myConverter}, UpdateSourceTrigger=PropertyChanged}" />
If you use UpdateSourceTrigger=PropertyChanged, on each user edit, the value will be passed to your ConvertBack method, and the result will be assigned to SomeValue of your model.
When user presses save button, you just save your model to database using whichever method you have for that. You don't need to explicitly update properties of your model, because they are already up-to-date. You can also use UpdateSourceTrigger=LostFocus (default one). Then whenever field loses focus - property in your model will be synchronized with it (again, through ConvertBack)
I have a TextBlock as follow:
<TextBlock Text="You don't have any more items." Visibility="{binding}"
and in code behind I defined a Stack called items as follow:
private Stack<Item> _items;
How do I bind the text visibility in xaml to visible when _item.Any is false?
There are several steps to achieving what you want to do and they are all described here
You need to create a value converter similar to this;
public class EmptyCollectionToVisibilityConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
var collection = (Stack<int>) value;
return collection.Any() ? Visibility.Visible : Visibility.Collapsed;
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
throw new NotImplementedException();
}
}
Then you need to add a reference to is in your resource dictionary in your xaml like this;
<views:EmptyCollectionToVisibilityConverter x:Key="EmptyCollectionToVisibilityConverter"/>
Finally bind your property in your view model to the visibility of your control and give the binding the converter like this;
Visibility="{Binding Items, Converter={StaticResource EmptyCollectionToVisibilityConverter}}"
Your property will probably need to be an observableCollection (which will mean changing the value converter example I gave you slightly.
I'd probably go with:
private Stack<Item> _items;
// bind to this property using converter
public bool IsVisible => !(_items?.Any(...) ?? false);
You shouldn't expose your _stack directly, but e.g. use methods to do something (because you need to rise notification every time you push/pop an item):
public void PushItem(Item item)
{
_items.Push(item);
OnPropertyChanged(nameof(IsVisible)); // implement INotifyPropertyChanged
}
In my program (MVVM WPF) there are lot of Enumerations, I am binding the enums to my controls in the view.
There are lot of ways to do it.
1) To bind to ComboBoxEdit(Devexpress Control). I am using ObjectDataProvider.
and then this
<dxe:ComboBoxEdit ItemsSource="{Binding Source={StaticResource SomeEnumValues}>
This works fine but in TabControl header it doesn't.
2) So, I thought of using IValueConverter that didnt worked either.
public object Convert(object value, Type targetType, object parameter,
CultureInfo culture)
{
if (!(value is Model.MyEnum))
{
return null;
}
Model.MyEnum me = (Model.MyEnum)value;
return me.GetHashCode();
}
public object ConvertBack(object value, Type targetType,
object parameter, CultureInfo culture)
{
return null;
}
on XAML:
<local:DataConverter x:Key="myConverter"/>
<TabControl SelectedIndex="{Binding Path=SelectedFeeType,
Converter={StaticResource myConverter}}"/>
3) The third way of doing this is to make a behavior dependency property
Something like this
public class ComboBoxEnumerationExtension : ComboBox
{
public static readonly DependencyProperty SelectedEnumerationProperty =
DependencyProperty.Register("SelectedEnumeration", typeof(object),
typeof(ComboBoxEnumerationExtension));
public object SelectedEnumeration
{
get { return (object)GetValue(SelectedEnumerationProperty); }
set { SetValue(SelectedEnumerationProperty, value); }
}
I want to know what is the best way to handle enumerations and binding to it. Right now I am not able to bind tabheader to the enums.
Here's a nicer way of doing it:
On your model, put this Property:
public IEnumerable<string> EnumCol { get; set; }
(Feel free to change the name to whatever suits you, but just remember to change it everywhere)
In the constructor have this (or even better, put it in an initialization method):
var enum_names = Enum.GetNames(typeof(YourEnumTypeHere));
EnumCol = enum_names ;
This will take all the names from your YourEnumTypeHere and have them on the property you'll be binding to in your xaml like this:
<ListBox ItemsSource="{Binding EnumCol}"></ListBox>
Now, obviously, it doesn't have to be a ListBox, but now you're simply binding to a collection of strings, and your problem should be solved.
Tearing my hair out here! I have this type-converter:
class CouponBarcodeToVisibilityConverterColumn : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
if (DesignerProperties.IsInDesignMode)
{
if ((string)parameter == "123456")
{
return Visibility.Visible;
}
return Visibility.Hidden;
}
if (value == null)
{
return Visibility.Visible;
}
var barcodesWanted = ((string)parameter).Split(System.Convert.ToChar("_"));
var actualBarcode = (string)value;
return barcodesWanted.Any(barcodeWanted => barcodeWanted == actualBarcode) ? Visibility.Visible : Visibility.Hidden;
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
return value;
}
}
I have a UserControl with the following Resources section:
<UserControl.Resources>
<converters:CouponBarcodeToVisibilityConverterColumn x:Key="CouponBarcodeToVisibilityConverter1"/>
</UserControl.Resources>
I have a model called Bet, it looks like this:
public class Bet : INotifyPropertyChanged
{
//Lots of other stuff
private string _barcode;
public string Barcode
{
get { return _barcode; }
set
{
if (value == _barcode) return;
_barcode = value;
OnPropertyChanged("Barcode");
}
}
//Lots of other stuff
}
In the ViewModel which is the DataContext of my user control I have an Observable Collection of Bet. Back to my user control, I have a stack panel, the data context of which is the aforementioned Observable Collection.
Inside the Stack Panel I have a DataGrid, the ItemsSource property is simply {Binding}, deferring the binding up the tree as it were.
Inside my DataGrid I have this column:
<DataGridCheckBoxColumn x:Name="IsEwColumn" Binding="{Binding Wagers[0].IsEw,UpdateSourceTrigger=PropertyChanged}" Header="Each Way" Visibility="{Binding Path=Barcode, Converter={StaticResource CouponBarcodeToVisibilityConverter1}, ConverterParameter=123456}" Width="Auto"/>
The other element of the binding works perfectly (the checkbox is ticked whenever it is supposed to be) but my type converter is not. The breakpoint doesn't even get hit. The Barcode property inside Bet is definitely equal to 123456.
What have I missed?
What you have here is a list of bets for the items source of the data grid.
If you think about it
Bet1 could evaluate to visible when passed via type converter.
Bet2 could evaluate to visible when passed via type converter.
Bet3 could evaluate to collapsed when passed via type converter.
How would the datacolumn be both visible and collapsed at the same time.
You can't bind to visibility like that, unless you had an overall variable on the list or something that it could bind to.