I was wandering if someone can explain to me how the Dependency Property DisplayMemberPath works?
I am trying to create Custom ItemsControl that has property like DisplayMemberPath of a ComboBox, in otherwords after setting the ItemsSource I want to be able to specify the Property to Display.
At the moment if I do somthing like:
<cc:MyControl ... DisplayMemberPath="MyObjectDescription" ... >
(Yes I have overridden the DisplayMemberPath, its besides the point).
It displays a list of items, but they each Display "MyObjectDescription", instead of the value that that Property holds for each object in the ItemsSource.
And I believe its because I am missing something in regards to how DisplayMemberPath Property works.
Thanks All. :)
There are two types of DisplayMemberPath. One that supports Binding and one where you have to set a string value. In your case as I can see you wish to implement the second one. To do so create a property inside your custom control of type string and name it DisplayMemberPath. Override the methode OnInitialized in your container with your custom logic where you tell the container to manipulate the path of the binding to DataContext by changing binding's path to the string value as you specified in DisplayMemeberPath. WPF calls OnInitalized once any control is completely initalized but before its about to get rendered. I hope this helps you any futher.
I'm assuming your control is like MyControl and MyControlItem like ListBox and ListBoxItem.
You can access the DisplayMemberPath of MyControl when the MyControlItem is being created and use it to get the data from the DataContext.
Bit late to party, but maybe other could be helped
If your purpose is barely to use Itemscontrol over ListBox/View, you may consider to define the Datatemplate for the itemscontrol's Items instead of packing this in a Usercontrol:
<ItemsControl ItemsSource="{Binding myObjectCollection}">
<ItemsControl.ItemTemplate>
<DataTemplate>
<TextBlock Text="{Binding myObjectProp}"/> (or whatever...)
</DataTemplate>
</ItemsControl.ItemTemplate>
</ItemsControl>
Related
Okay so in wpf xaml markup the data binding features allow for data binding a list to a listView. To do I specified the DataContext and set the ItemSource to the DataContext. This works and the listView is populated with the items. The items though are objects and to be able to have the displayed item in the list view as a string property of get set implementation from the object enumerated in the list view I am attempting to use an Item Template. Though this is not working and I'm uncertain why.
How exactly does Item Template and the Data Binding function in this scenario? And what would be workable solutions to this problem? Is there a way to specify the property in the text box as being local to the enumerated objects. Please Help I've honestly been working on this for a while and research hasn't provided the answers.
ItemList is a list of objects. ItemName is a string property of ItemList. The ItemSource and DataContext works but the textblock does not.
Preferably a solution using only xaml.
<ListView DataContext="this.ItemList" ItemsSource="{Binding }" Name ="Items">
<ListView.ItemTemplate>
<DataTemplate>
<TextBlock Text="{Binding ItemName}" >
</TextBlock>
</DataTemplate>
</ListView.ItemTemplate>
Except for some unconventional ways of working pointed out by Clemens, I think the only actual error you make is the fact that ItemName is a property of ItemList instead of the enumerated objects' class.
You ask "Is there a way to specify the property in the text box as being local to the enumerated objects". Well, this is the actual case: the TextBlock's datacontext IS the enumerated object. More precisely: all bindings in the itemtemplate will go look in the enumerated object unless the binding explicitly tells otherwise. So, if your enumerated object has eg. a string property ObjectName, its value will definitely get bound and shown by the textblock.
I have a user control that has one dependency property. In my window I have a list of objects, and I am creating a uniform grid consisting of my user control. I am setting the ItemsSource to my list of objects, but I need to pass each respective object to the user control. Please see the code below - I need to pass in the Participant object to the LadderControl.
<ItemsControl Grid.Row="2" Name="Participants" ItemsSource="{Binding Path=MyEvent.Participants}">
// more code here, irrelevant
<ItemsControl.ItemTemplate>
<DataTemplate>
<ladder:LadderControl Participant="CURRENT_ITEM_IN_PARTICIPANTS_LIST"/>
</DataTemplate>
</ItemsControl.ItemTemplate>
</ItemsControl>
Is there a way I can do this ? Should I be thinking about using a different pattern ?
Thanks
Just do the below, as the Participant is the context of each item
<ladder:LadderControl Participant="{Binding}"/>
You can simply access the DataContext Property in LadderControl to access the currrent participant.
There is no need for a separate dependency property.
class LadderControl
{
...
public IParticipant Participant
{
get{ return DataContext as IParticipant; }
}
...
One solution is to simply do:
<ladder:LadderControl Participant="{Binding Path=.}"/>
{Binding Path=.} should bind to the current element in the ItemsSource list.
I have a View that is linked to my ViewModel using a DataTemplate, like this
<DataTemplate DataType="{x:Type ViewModels:ViewModel}">
<Views:View />
</DataTemplate>
The ViewModel holds a property ProcessOption that is of type MyEnum?, where MyEnum is a custom enumeration that has let's say 3 values: Single, Multiple and All. I am trying to bind a combobox to this property, so the approach I am following is:
ViewModel has a property of List<string> that is
public List<string> Options
{
get
{
return Enum.GetNames(typeof(MyEnum)).ToList();
}
}
to which I bind the ItemsSource property of the Combobox. Then, in addition to the ProcessOption property, the ViewModel also has an OptionName property (of string), which is intended to hold the selected option's name. The ViewModel implements INotifyPropertyChanged and both properties raise the PropertyChanged event in their setters. The binding I am using then is:
<ComboBox ItemsSource="{Binding Options}"
SelectedItem="{Binding OptionName}"
SelectedValue="{Binding ProcessOption}"/>
This works fine up to this point. Initially the combobox is empty and both properties are null, and when the user selects an option this is propagated to the ViewModel as it should.
The problem appears when I load the data from a Database, and I want to load the controls with initial values. In this case, in the ViewModel's constructor I have this:
this.ProcessOption = objectFromDB.ProcessOption // this is the value restored from DB, let's say it is MyEnum.Multiple
this.OptionName = Options.First(x => x.Equals(Enum.GetName(typeof(MyEnum), objectFromDB.ProcessOption)));
The problem is, although the above sets the two properties to their correct values, they are later set to null from the Combobox binding, so the initial values are not kept. I have also tried to do something like if (value == null) { return; } in the properties' setters, in which case they have the correct values after the View loads, however the Combobox still does not display the correct option, it is empty.
I should also note that I've also tried setting IsSynchronisedWithCurrentItem and it doesn't make any difference, apart from the fact that the first element is displayed instead of the combobox being empty.
Can anyone help with this binding? Any help will be very much appreciated, this is driving me crazy!
<ComboBox ItemsSource="{Binding Options}"
SelectedItem="{Binding OptionName}"
SelectedValue="{Binding ProcessOption}"/>
Your binding doesn't look like it should work at all -- you don't have TwoWay binding set up, and I think SelectedItem and SelectedValue is an either/or proposition.
I suggest that you get rid of OptionName and just bind SelectedItem to ProcessOption (TwoWay) with an IValueConverter that will convert to/from string.
i have a datatemplate declared in xaml.
for e.g.
<DataTemplate x:Key="TestTemplate">
<StackPanel>
<TextBox Name="txtBox" Visibility="Visible"></TextBox>
</StackPanel>
</DataTemplate>
I wish to set the binding for txtBox in code behind before the element is generated because i have different binding paths for different elements that get generated
I can get the template in the code behind as :
DataTemplate tmplt = FindResource("TestTemplate") as DataTemplate;
but i am not sure what to do next. How to get the the txtBox reference to set the binding.
We have to remember one thing that Templates are not instantiated UI controls. They are streamed obejcts in XAML and are shared between UI elements. So if you edit a dataTemplate and change its stucture (by adding, editing, deleting an element under the template) it would change the one data template which is shared among controls. Thus other elements using that template will also be affected by the change.
Now lets address your issue of adding a dynamic biding to a textbox. You say each generated textbox will have different binding paths. So this definitely does NOT call for changing the data template itself!
You will have to access the text box and add dynamic bindings to it AFTER the textbox's is generated.
I see that your binding differs based on your "situation", so why cant you use TemplateSelector? Template selector will decide which data template (having one specific binding applied to the TetxBox) at runtime.
The first part of answer - is FindName() method.
example:
DataTemplate tmplt = FindResource("TestTemplate") as DataTemplate;
TextBox my = (TextBox)tmplt.FindName("txtBox");
try out this, it should help to get access to TextBox control. I think that you know how to bind to. If you want your DataBinding behave different way, use MultiBinding and Converter.
EDIT
public class GeneralObject
{
private object someObject;
public GeneralObject(object initObject)
{
this.someObject = initObject;
}
//If you want to bind to some text, for example
public string Text
{
get
{
//I think you know which objects are coming as input
if (this.someObject is SpecialClass1)
return ((SpecialClass1)this.someObject).SpecialClass1TextProperty;
if (this.someObject is SpecialClass2)
return ((SpecialClass2)this.someObject).SpecialClass2TextProperty;
//and so on.
}
}
}
EDIT 2
One more possible way
So I remember, that WPF have ContentControl!
<ContentControl Content="{Binding Path=CurrentObject}"/>
But in this case you have to create number of DataTemplate's, every Template for one class.
<DataTemplate DataType="{x:Type local:SpecialClass1}">
...
</DataTemplate>
<DataTemplate DataType="{x:Type local:SpecialClass2}">
...
</DataTemplate>
<!--and so on-->
WPF resolve DataTypes of ContentControl.Content property, and put to the ContentControl right DataTemplate.
I'm building a custom WPF control that derives from TabControl. In the ControlTemplate, I'm using a ItemsControl to display a list that is being bound from the template (an observable collection of type FileMenuItem). During program execution, I'm getting the following error in the output window:
ItemTemplate and ItemTemplateSelector
are ignored for items already of the
ItemsControl's container type;
Type='FileMenuItem'
The type FileMenuItem is derived from MenuItem. If I change the base class to DependencyObject, the code actually runs and the template is applied (so that's an option). I googled the error and couldn't find anything about it, has anyone run into this while developing custom controls? Even though I have a workaround, I'd like to understand what's happening, and I think using the MenuItem as a base class is a cleaner implementation.
I can post more code if it would help. Thanks!
The purpose of a DataTemplate (like ItemTemplate) is to provide a visualization for a data object. Specifically, it defines a set of elements to add to the visual tree in place of the data given to an ContentPresenter or ItemsPresenter. In your case your source list is a collection of objects that are already able to be added directly to the visual tree for display in the UI.
You can see this in the following simplified example where only "Three" shows up in Red because the first two items are defined in a form that can be displayed directly by ComboBox.
<ComboBox>
<ComboBox.ItemTemplate>
<DataTemplate>
<TextBlock Text="{Binding}" Foreground="Red"/>
</DataTemplate>
</ComboBox.ItemTemplate>
<ComboBoxItem>One</ComboBoxItem>
<ComboBoxItem>Two</ComboBoxItem>
<sys:String>Three</sys:String>
</ComboBox>