In this example:
<TextBox Name="textBox1" Height="23" Text="some text" HorizontalAlignment="Left" Margin="69,12,0,0" VerticalAlignment="Top" Width="120" />
<Label Content="{Binding Path=Text, ElementName=textBox1}" Height="28" HorizontalAlignment="Left" Margin="235,12,0,0" Name="label1" VerticalAlignment="Top" />
whatever I type on the textbox will be displayed on the label. I am learning xaml and I believe I understand most of the Bindings such as this one. But I think even though I understand what is happening, it will be nice to understand what the Binding keyword refers to? for example I can have:
<ListView ItemsSource="{Binding}" Name="lv1" />
I am having a hard time understanding what binding actually refers to? There is nothing after the Binding keyword, so what is it binding to? Does it refer to that control? Is it similar to the this keyword used in c# where it will refer to the current instantiated object of a class?
It's not a keyword, it's a markup extension.
Bindings always bind to the Path relative to the source, if there is no path they bind directly to the source, possible sources are the DataContext which is used implicitly if no other source is specified and ElementName, Source and RelativeSource. Please read the overview if you have not done so yet.
This is a binding to the Property DataContext of the window. If there is a list of elements in
that, you will see it in the ListBox.
For example type DataContext = new List<string> { "A", "B", "C" }; in the constructor of your window after InitializeComponents(); and you will see that list in your ListBox.
Related
I have a UserControl that I want to participate in data binding. I've set up the dependency properties in the user control, but can't get it work.
The uc displays the correct text when I call it with static text (e.g BlueText="ABC") . When i try to bind it to a local public property, it is always blank.
<src:BlueTextBox BlueText="Feeling blue" /> <!--OK-->
<src:BlueTextBox BlueText="{Binding Path=MyString}" /> <!--UserControl always BLANK!-->
<TextBox Text="{Binding Path=MyString}" Width="100"/> <!--Simple TextBox Binds OK-->
I've boiled the code down to the following simplified example. Here is the XAML of the UserControl:
<UserControl x:Class="Binding2.BlueTextBox" ...
<Grid>
<TextBox x:Name="myTextBox" Text="{Binding BlueText}" Foreground="Blue" Width="100" Height="26" />
</Grid>
Here is the code behind of the UserControl:
public partial class BlueTextBox : UserControl
{
public BlueTextBox()
{
InitializeComponent();
DataContext = this; // shouldn't do this - see solution
}
public static readonly DependencyProperty BlueTextProperty =
DependencyProperty.Register("BlueText", typeof(string), typeof(BlueTextBox));
public string BlueText
{
get { return GetValue(BlueTextProperty).ToString(); }
set { SetValue( BlueTextProperty, value.ToString() ); }
}
This seems like it should be really easy, but I can't make it work. Thanks for your help!
More info: When i was trying the fix suggested by Eugene, I noticed some peculiar behavior. I added a PropertyChangedCallback to the metadata; this allows me to watch the value of BlueText getting set. When setting the string to a static value (="feeling blue") the PropertyChanged event fires. The data binding case does not fire PropertyChanged. I think this means the data-bound value is not getting sent to the UserControl. (I think the constructor does not get called in the static case)
Solution: The problems were correctly identified by Arcturus and jpsstavares. First, I was overwriting the data binding when is set DataContext=this in the constructor of the control. This prevented the data bound value from getting set. I also had to name the control x:Name=root, and specify the Binding ElementName=root int the XAML. To get the TwoWay binding, I needed to set Mode=TwoWay in the caller. Here is the correct code:
<src:BlueTextBox BlueText="{Binding Path=MyString, Mode=TwoWay}}" /> <!--OK-->
Now the XAML in the UserControl:
<UserControl x:Class="Binding2.BlueTextBox" x:Name="root"...
<Grid>
<TextBox x:Name="myTextBox" Text="{Binding ElementName=root, Path=BlueText}" Foreground="Blue" Width="100" Height="26" />
</Grid>
Finally I removed the DataContext=this in the constructor of the UserControl.
public BlueTextBox()
{
InitializeComponent();
//DataContext = this; -- don't do this
}
Thanks everyone for the tremendous help!
You set the DataContext in the Control to itself, thus overwriting the DataContext when using this Control in other controls. Taking your binding as example in your situation:
<src:BlueTextBox BlueText="{Binding Path=MyString}" />
Once loaded and all the Datacontext is set, it will look for the path MyString in your BlueTextBox thing control due to you setting the DataContext to it. I guess this is not how you intended this to work ;).
Solution:
Change the text binding either one of the 2 bindings:
{Binding RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type src:BlueTextBox}}, Path=BlueText}
or
Name your control Root (or something like that)
<UserControl x:Name="Root"
{Binding ElementName=Root, Path=BlueText}
And remove the
DataContext = this;
from the constructor of your UserControl and it should work like a charm..
I think in this case you need to set the ElementName property in the binding. Something like this:
<UserControl x:Class="Binding2.BlueTextBox" x:Name="blueTextBox"...
<Grid>
<TextBox x:Name="myTextBox" Text="{Binding ElementName=blueTextBox, Path=BlueText}" Foreground="Blue" Width="100" Height="26" />
</Grid>
Possibly you need to add to your property FrameworkPropertyMetadata where specify FrameworkPropertyMetadataOptions.AffectsRender and AffectsMeasure.
FrameworkPropertyMetadataOptions enumeration MSDN article
I know this is an old topic but still.
Also mention the PropertyChangedCallback on the UIPropertyMetadata during registering your DP
I currently have a large license file embedded in my program that I'd like to bind a RichTextBox to. I've tried multiple methods but found no good way to do this without including something in the code-behind. I'd prefer to bind the document in the XAML itself. As an analogue, I currently have an image bound like so:
<Image Height="25" HorizontalAlignment="Left" Margin="12,12,0,0" Name="image1" Stretch="Fill" VerticalAlignment="Top" Width="23" Source="Resources\68PVb9k.png" />
Is there any way to achieve this with a RichTextBox document? If I attempt to bind the document directly I get an error:
"A 'Binding' cannot be set on the 'Document' property of type 'RichTextBox'. A 'Binding' can only be set on a DependencyProperty of a DependencyObject."
So something like:
<RichTextBox Name="richTextBox1" Document="{Binding Path=Resources\InternalLicense.txt}" IsEnabled="False"/>
Won't work. (I realize the obvious formatting issues there. It's just an example)
TextBox IsReadOnly = true
TextBoxBase.IsReadOnly Property
I need to databind into a element inside my custom class. i've given the ItemSource as the ObservableCollection of telerik:RadTransitionControl via an attached property. However, I need to provide the image member as the source to Image control. I tried the following method and was unsuccessful.
<Grid Background="Black">
<telerik:RadTransitionControl x:Name="radControl" adRotator:AdRotatorExtensions.ItemChangeDelay="0:0:3"
adRotator:AdRotatorExtensions.CurrentSelectedIndex="0"
adRotator:AdRotatorExtensions.IndexChanged="{Binding TopItemCommand, Mode=OneWay}"
adRotator:AdRotatorExtensions.ItemsSource="{Binding Path=ImagePaths}"
VerticalAlignment="Center"
HorizontalAlignment="Center" Width="650">
<telerik:RadTransitionControl.Transition>
<telerik:MotionBlurredZoomTransition />
</telerik:RadTransitionControl.Transition>
<telerik:RadTransitionControl.ContentTemplate>
<DataTemplate>
<Image Source="{Binding Path=ImagePaths.AdImage}" />
</DataTemplate>
</telerik:RadTransitionControl.ContentTemplate>
</telerik:RadTransitionControl>
</Grid>
an ImagePaths object is already set as the DataContext for the item. this means that the binding is already pointing (so to speak) at an instance of the object. so, when you tell it to bind on ImagePaths.AdImage it does not know how to find the property you are looking for. Good news is, all you have to do is provide the path on the object-- remove the ImagePaths part (and the dot) and you should be good to go.
for example...
class something
{
public string someImage {...}
}
<DataTemplate> <!--------- the data context of this item is an instance of
my "something" class, so i need to set the path
to be the property on the object --->
<Image Source="{Binding Path=someImage}" />
</DataTemplate>
here is a very helpful article on debugging bindings in WPF
for more info here is an excellent article on MSDN
here is a datatemplate article from Dr. WPF
To begin I would like to apologize for my english which is far from perfect (its not my native language...).
I've a problem related to databinding in my XAML code. I've a combox which is supposed to list all graphical nodes that I drop on a custom canvas. My graphical nodes are referenced in a list graphCanvas.uinodes , and each node has a name. And that's what I want to show in my combobox.
So I tried something like this:
<ComboBox ItemsSource="{Binding ElementName=graphCanvas, Path=uinodes/name}"
Height="23" HorizontalAlignment="Left" Name="comboBox1"
VerticalAlignment="Top" Width="71" Foreground="Black" />
But even after drawing nodes on my canvas my combox is empty...
Any clue?
Thanks.
A binding using ElementName finds the WPF element with that name. I doubt that you've subclassed Canvas and added a uinodes property to it, which is the only way that Path would find something even if the path syntax were correct, which it's not.
If you look in the Output window when you run your program, you'll see an error message that tells you why the binding isn't working. That's a start.
But even then, you won't get what you want with this approach. What you probably want looks more like:
<ComboBox ItemsSource="{Binding ElementName=graphCanvas, Path=uinodes}"
DisplayMemberPath="name"/>
or even
<ComboBox ItemsSource="{Binding ElementName=graphCanvas, Path=uinodes}">
<ComboBox.ItemTemplate>
<TextBlock Text="{Binding name}"/>
</ComboBox.ItemTemplate>
</ComboBox>
Your binding (specifically the Path assignment) looks wrong. Assuming uinodes is an Enumerable of some sort it looks as though you are trying to bind to the `name' property of the collection, which does not exist. Try this:
ItemsSource="{Binding ElementName=graphCanvas, Path=uinodes}" DisplayMemberPath="name"
As an aside, you can use the output window to see any binding errors.
I have a UserControl that I want to participate in data binding. I've set up the dependency properties in the user control, but can't get it work.
The uc displays the correct text when I call it with static text (e.g BlueText="ABC") . When i try to bind it to a local public property, it is always blank.
<src:BlueTextBox BlueText="Feeling blue" /> <!--OK-->
<src:BlueTextBox BlueText="{Binding Path=MyString}" /> <!--UserControl always BLANK!-->
<TextBox Text="{Binding Path=MyString}" Width="100"/> <!--Simple TextBox Binds OK-->
I've boiled the code down to the following simplified example. Here is the XAML of the UserControl:
<UserControl x:Class="Binding2.BlueTextBox" ...
<Grid>
<TextBox x:Name="myTextBox" Text="{Binding BlueText}" Foreground="Blue" Width="100" Height="26" />
</Grid>
Here is the code behind of the UserControl:
public partial class BlueTextBox : UserControl
{
public BlueTextBox()
{
InitializeComponent();
DataContext = this; // shouldn't do this - see solution
}
public static readonly DependencyProperty BlueTextProperty =
DependencyProperty.Register("BlueText", typeof(string), typeof(BlueTextBox));
public string BlueText
{
get { return GetValue(BlueTextProperty).ToString(); }
set { SetValue( BlueTextProperty, value.ToString() ); }
}
This seems like it should be really easy, but I can't make it work. Thanks for your help!
More info: When i was trying the fix suggested by Eugene, I noticed some peculiar behavior. I added a PropertyChangedCallback to the metadata; this allows me to watch the value of BlueText getting set. When setting the string to a static value (="feeling blue") the PropertyChanged event fires. The data binding case does not fire PropertyChanged. I think this means the data-bound value is not getting sent to the UserControl. (I think the constructor does not get called in the static case)
Solution: The problems were correctly identified by Arcturus and jpsstavares. First, I was overwriting the data binding when is set DataContext=this in the constructor of the control. This prevented the data bound value from getting set. I also had to name the control x:Name=root, and specify the Binding ElementName=root int the XAML. To get the TwoWay binding, I needed to set Mode=TwoWay in the caller. Here is the correct code:
<src:BlueTextBox BlueText="{Binding Path=MyString, Mode=TwoWay}}" /> <!--OK-->
Now the XAML in the UserControl:
<UserControl x:Class="Binding2.BlueTextBox" x:Name="root"...
<Grid>
<TextBox x:Name="myTextBox" Text="{Binding ElementName=root, Path=BlueText}" Foreground="Blue" Width="100" Height="26" />
</Grid>
Finally I removed the DataContext=this in the constructor of the UserControl.
public BlueTextBox()
{
InitializeComponent();
//DataContext = this; -- don't do this
}
Thanks everyone for the tremendous help!
You set the DataContext in the Control to itself, thus overwriting the DataContext when using this Control in other controls. Taking your binding as example in your situation:
<src:BlueTextBox BlueText="{Binding Path=MyString}" />
Once loaded and all the Datacontext is set, it will look for the path MyString in your BlueTextBox thing control due to you setting the DataContext to it. I guess this is not how you intended this to work ;).
Solution:
Change the text binding either one of the 2 bindings:
{Binding RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type src:BlueTextBox}}, Path=BlueText}
or
Name your control Root (or something like that)
<UserControl x:Name="Root"
{Binding ElementName=Root, Path=BlueText}
And remove the
DataContext = this;
from the constructor of your UserControl and it should work like a charm..
I think in this case you need to set the ElementName property in the binding. Something like this:
<UserControl x:Class="Binding2.BlueTextBox" x:Name="blueTextBox"...
<Grid>
<TextBox x:Name="myTextBox" Text="{Binding ElementName=blueTextBox, Path=BlueText}" Foreground="Blue" Width="100" Height="26" />
</Grid>
Possibly you need to add to your property FrameworkPropertyMetadata where specify FrameworkPropertyMetadataOptions.AffectsRender and AffectsMeasure.
FrameworkPropertyMetadataOptions enumeration MSDN article
I know this is an old topic but still.
Also mention the PropertyChangedCallback on the UIPropertyMetadata during registering your DP