In WPF and Silverlight you can make a view model object and set it into the DataContext of a control when the control is constructed at runtime. You can then bind properties of the visual object to properties in your DataContext.
One way to set the binding is to type the binding directly into the tag:
<TextBox Text="{Binding Path=Description}"/>
And this will bind the textbox to the Description property in the view model.
The problem with typing in the binding is that you may make a typing mistake. (And you will almost certainly make a mistake if you have hundreds of bindings to make.)
In Expression Blend there is a little white dot beside the Text property in the Properties window. This brings up a menu from which you can Create Data Binding.
How can I get my view model properties to show in the Create Data Binding dialog so that I can select them.
Will the configuration of data binding in Blend interfere with setting my view model into the DataContext at runtime?
One technique is to include the VM as a resource in your view:
<UserControl>
<UserControl.Resources>
<local:YourViewModel x:Key="ViewModel"/>
</UserControl.Resources>
</UserControl>
You can then reference that as DataContext="{StaticResource ViewModel}" elsewhere.
Can't say I like it, but I can't say I like any of the view-first idiosynchrasies that Blend imposes on your design.
I experimented with Blend to find the drag and drop approach to data binding which still lets you override your view model in code easily.
First make your view model object which implements INotifyPropertyChanged and raises the notify event in the setters. The view models can be hierarchical. For example you could have an ObservableCollection within your main view model.
In Blend open up your page or control and go to the data tab.
On the right open the menu under the "Add live data source" icon.
Pick "Define new object data source"
Select your top level view model class and confirm the dialog
In my experiments I found that it was important to bind the data source to where I wanted it first or else Blend might make a less than optimal configuration if I didn't do the next step first.
Open the Objects and Timeline window in Blend
Select the root object, for example UserControl
Open Properties and verify that the root object is selected
Find DataContext and click the square to open the menu and select DataBinding
Select the data source that was just previously created
Now that the data source has been created data binding is very easy.
put some controls on the page
open the Data window
from the DataSource for your view model drag properties onto the controls to create the bindings or set the binding from the Properties window.
Now you can create you live view model object in the constructor of the control
public MainPage()
{
// Required to initialize variables
InitializeComponent();
mVm = new MyViewModel();
this.DataContext = mVm;
}
private MyViewModel mVm;
Add any initialization to retrieve data and you are ready to go.
I have a screen cast on my blog Blendable MVVM : Introduction and Databinding which shows setting this up for Siverlight.
Essentially you create the ViewModel as the DataContext of the UserControl using the "New Object Initialiser" and then using the "Explicit Data Context" tab of the Binding dialog for the controls themselves.
Hope this helps.
Related
I am coming from programming with WinForms and now start to change into WPF. In WinForms I could easily bind a DataGrid before Runtime, to adjust the columns without coding everything.
The WPF-Datagrid has the property "ItemsSource", but I don't understand how to bind it in editor. I have already a DataSource which refers to a SQL-Database, but it will not be shown in the property window.
How to do this?
Screenshot
you have to expose your collection as a public property
make it visible in the xaml (namespace include)
set up your DataContext correctly
create the binding in XAML and set up the columns, like here
If you want to see the changes in your collection online, you have to use ObservableCollection<>
I'm creating custom control and because I need to do lot's of binding inside a style/template it makes perfect sense to go with MVVM. Where do I declare dependency properties then?
Do they stay in control class? How do I link them to VM?
See my answer to your other question about custom controls and view models. Here's the short version:
Custom controls shouldn't have view models.Don't set the data context of your own control. That's reserved for the consumer.All of your dependency properties should be declared in your MyCustomControl.cs file.Use TemplateBinding in your genric.xaml because it's more efficient that Binding.
To put it another way, what's the view model for a Border or a Button? Answer: they don't have one because they're just controls. UserControls have view models, but controls just present and interact with the data which you give them (where? In your UserControl). Custom control development is probably the hardest thing for a seasoned MVVM developer: your reflex is to make a view model, but that reflex is unfortunately wrong. I know because I've made this mistake myself.
Dependency Properties could be delared in the Control they are belongs to.
When following MVVM in WPF/Silverlight the common approach is to set ViewModel as DataContext of the appropriate View. So you would be able to link custom Dependency Properties to the ViewModel properties using Bindings in XAML.
Let's assume you already set ViewMosel to DataContext of the View:
var view = new UserView
{
DataContext = new UserViewModel { Name = "Custom Name" }
};
public class UserViewModel
{
string Name { get; set; }
}
UserView.xaml:
<TextBlock Text="{Binding Name}" />
When creating a custom control, the control itself is a view model. Declare dependency properties on it to expose bindings that users of the custom control can leverage. For example if you have a timeline control, you might have properties like StartDate and EndDate on the control exposed as dependency properties. Your Controls Default Template would make template bindings to the dependency properties. A consumer of your control might then have a project timeline viewmodel that he binds to the properties on the control.
The primary purpose of a custom control is to provide behavior and a default look and feel for that behavior which is easy to override (by providing a new template). Hope this helps.
I have a ContentControl in xaml defined as:
<ContentControl Micro:View.Model="{Binding ProductionGrid}" />
I use the View.Model as the control is embedded in a docking panel.
My ViewModel has the property defined and it set in the constructor of the ViewModel and uses constructor injection to create the instance.
The View gets instantiated, but I cannot access the model that was created in the ViewModel, it seems to create a new model when trying to get the instance from the xaml.cs constructor of the View.
var model = Caliburn.Micro.ViewModelLocator.LocateForView(this) as DynamicDataGridViewModel;
How can I correctly get the model that should be associated with the View when it's created?
If the ContentControl is embedded in a docking panel you can just name the ContentControl x:Name="ProductionGrid" and shouldn't need Micro:View.Model="{Binding ProductionGrid}"
The View gets instantiated, but I cannot access the model that was
created in the ViewModel, it seems to create a new model when trying
to get the instance from the xaml.cs constructor of the View.
You mean the ViewModel gets instantiated?
So the binding works? I'd have to look but I don't know if CM will find ProductionGridView from ProductionGrid, it might, I'm not sure. ProductionGridViewModel and ProductionGridView would work.
You shouldn't need to code anything in the xaml.cs constructor, in fact, I delete the xaml.cs files.
I've created a new WPF project, and threw in a DataGrid. Now I'm trying to figure out the easiest way to bind a collection of data to it.
The example I downloaded seems to do it in the window c'tor:
public partial class MainWindow : Window
{
public MainWindow()
{
InitializeComponent();
DataContext = new ViewModel();
}
}
But then the bindings don't seem to appear in the Visual Studio's Properties window. I'm pretty sure there's a way to set the data context in XAML too... it would make me even happier if I could do it directly through the properties window, but all the Binding options are empty. What's the typical approach?
Edit: At 14 minutes, he starts to talk about other methods of setting the data context, such as static resources, and some "injection" method. I want to learn more about those!
What I typically do is use MVVM. You can implement a simplified version by setting the data context in your code behind and having a model type class that holds your data.
Example: In your code behind
DataContext = Model; // where Model is an instance of your model
then in your view
<DataGrid .... ItemsSource="{Binding SomeProperty}">....
Where SomeProperty is an enumerable property on your view model
You can also set a data context in XAML by using the DataContext property
<uc:SomeUserControl DataContext="{Binding AnotherProperty}"....
This will run your user control within the DataContext of the AnotherProperty on your model.
Note that this is grosely simplified but it'll get you on your way.
Have a look at the MVVM design pattern. This pattern is very suitable for wpf applications.
There is described where to store your data and how to bind your ui to the data.
I have a WPF user control ...which is in MVVM. The user control(which contains a listview) need data from the page (where it is included). I have to set a property to get this data input. Will this comply with MVVM...if not, what is the way for the same?
I'm afraid this won't be correct in MVVM design pattern. try to stick to your view model to define properties. Why don't you consider moving that property to control's vm?
Use an ObservableCollection rather.
ObservableCollection<myModel> myOC = new ObservableCollection<myModel>();
where myModel is a class that has to be constructed transforming your columns in the DataTable to Properties.
In your MainViewModel, loop through the DataReader and create myOC out of it.
Now bind myOC to a ListView in your page.
The DataTemplate of ListView should be a view(UserControl) drawing data from a ViewModel constructed out of myModel
But your UserControl has the entire ListView inside. If that is on purpose, then let me know the entire design to give a better idea.