I haven't used WPF that much so the solution to this is probably pretty easy.
In the ide I'm developing it will have multiple controls(text editor) each being hosted in a tab, much like VS does for each source file. When the user clicks new the "host" creates a new EditorWindow(a usercontrol), creates a new tab, and tells the tab to display the EditorWindow it created, and then updates a property called currentWindow (of type EditorWindow) with the one that's currently active. Inside the EditorWindow is the text editor whose name is textEditor(also a property). What I'm trying to do is take this code from the quick start source of the text editor control I'm using
<StackPanel>
<CheckBox Checked="EditiorOptionsChecked" IsChecked="{Binding ElementName=Control, Path=currentWindow.textEditor.IsIndicatorMarginVisible}" Content="Indicator margin visible" />
<CheckBox Checked="EditiorOptionsChecked" IsChecked="{Binding ElementName=Control, Path=currentWindow.textEditor.IsLineNumberMarginVisible}" Content="Line number margin visible" />
<CheckBox Checked="EditiorOptionsChecked" IsChecked="{Binding ElementName=Control, Path=currentWindow.textEditor.IsRulerMarginVisible}" Content="Ruler margin visible (useful for fixed-width fonts only)" />
<CheckBox Checked="EditiorOptionsChecked" IsChecked="{Binding ElementName=Control, Path=currentWindow.textEditor.IsSelectionMarginVisible}" Content="Selection margin visible" />
</StackPanel>
put that in the host controls xaml, and bind the checkboxes to the syntax editor. I've tried a couple different things to no avail. Control is the name of the window hosting all the tabs, and path is obviously supposed to be the property that the checkboxes are bound too. I'm pretty sure the problem is that at initial run-time currentWindow isn't initialized so therefore my bindings aren't ever getting updated, but I'm at a loss as to how to fix this issue. Thanks!
Since you are new to WPF, you may not know that properties have to implement some sort of change notifications in order for bindings to work. For instance, if any of the properties in the the path "currentWindow.textEditor.IsIndicatorMarginVisible" change, you need to inform the binding engine that it has changed. If you implement these properties as DependencyPropertys, the change tracking comes for free. Otherwise, you should implement INotifyPropertyChanged.
I've found that the Snoop utility is the easiest way to do quick binding debugging, you should try using it and see if it tells you anything useful on the bound properties.
Related
My goal is to display the X position of my control in a TextBlock as I drag it around.
xmlns:mb="http://schemas.microsoft.com/xaml/behaviors"
<cc:CardControl Name="SevenOfSpades" Canvas.Left="350" Canvas.Top="124" Width="60" Height="80" Face="S7">
<mb:Interaction.Behaviors>
<mb:MouseDragElementBehavior ConstrainToParentBounds="True"/>
</mb:Interaction.Behaviors>
</cc:CardControl>
<TextBlock Text="{Binding ElementName=SevenOfSpades, Path=(mb:Interaction.Behaviors)[0].X}"/>
I'm struggling with the syntax of the Binding Path. At runtime I get an exception:
InvalidOperationException: Property path is not valid. 'Interaction' does not have a public property named 'Behaviors'.
The property is there because the drag works when the TextBlock is removed. I've tried various combinations of parentheses, I even tried x:static. Any help?
Edit
Having reread WPF Attached Property Data Binding, it does not solve my problem. Path= is in the Xaml and parentheses are included. The error is not a binding error it's a runtime error that occurs inside InitializeComponent.
MouseDragElementBehavior is part of the Microsoft.Xaml.Behaviors.Wpf Nuget package installed into my project.
Ah, ok. In that case, the code for MouseDragElementBehavior is most certainly available, and even if it wasn't you could just open up the assembly with JustDecompile or something and browse it that way.
If you check the documentation for MouseDragElementBehavior you'll see this:
XProperty Dependency property for the X position of the dragged
element, relative to the left of the root element.
So basically you're trying to bind one dependency property (TextBlock.Text) to another (MouseDragElementBehavior.X), but in order for this to work they have to be part of the same visual or logical tree (which they aren't, MouseDragElementBehavior is a behavior). If one of them was an attached property then you could bind them directly, but in your case you have to link them together with either a property in your DataContext that supports INPC, or some kind of proxy object.
However, even if you do this, you're going to run into problems. If you click the "Go to Live Visual Tree" button while your application is running and look at the properties for your SevenOfSpades control you'll see this:
So far, so good. Now drag the control around a bit and repeat this process. Suddenly a RenderTransform field has appeared:
Looking back at the code for MouseDragElementBehavior reveals that sure enough, that behaviour does the drag by changing the render transform.
So basically you're trying to set the position with Canvas.Top/Canvas.Left, but the behaviour is setting it by applying a render transform offset. Pick one. I personally use MVVM where everything is implemented in the view model layer, so it's easy to bind Canvas.Top/Canvas.Left to properties there. If you want to continue using MouseDragElementBehavior then you'll need to bind both the position of your cards, as well as your TextBlock text, to the render transform instead:
<Canvas>
<Rectangle Name="SevenOfSpades" Width="60" Height="80" Fill="Blue">
<Rectangle.RenderTransform>
<TranslateTransform X="350" Y="124" />
</Rectangle.RenderTransform>
<mb:Interaction.Behaviors>
<mb:MouseDragElementBehavior ConstrainToParentBounds="True" />
</mb:Interaction.Behaviors>
</Rectangle>
<TextBlock Text="{Binding ElementName=SevenOfSpades, Path=RenderTransform.Value.OffsetX}" />
</Canvas>
I have a listBox using an itemTemplate that contains the following line:
<Image Source="{Binding MyProperty.PossiblyNullObject.UrlProperty}"/>
Bound to this listBox is a model view collection that loads components of the items in the collection on a separate thread. The 'PossiblyNullObject' may not be set to a value when the xaml code is first rendered by the composition engine.
How does WPF handle this? Does it use a default value(no image source so no image) and continue on? Does it wait? Does it automatically detect when the value is initialized and rerenders with the new source? How does it not throw object null exceptions in the same way it would if I called 'MyProperty.PossiblyNullObject.UrlProperty' programmatically? How can I reproduce this functionality in my own code when I try to call it?
Thanks for any suggestions. I am embarrassingly new to WPF and I'm trying to tackle a problem out of my depth. The image load is a perf problem so I found a solution to load, decode, then freeze the image source on a background thread so it wouldn't lock up the UI. Unfortunately, I ran across this null exception problem when I tried replacing the image source binding with my solution that calls the same property. WPF somehow handles the possible null objects and I'd like to do it the same way to keep things clean.
In BindingBase have two properties: TargetNullValue and FallbackValue.
TargetNullValue returns your value when the value of the source is null.
FallbackValue returns your value when the binding is unable to return a value.
Example of using:
<!-- xmlns:sys="clr-namespace:System;assembly=mscorlib" -->
<Window.Resources>
<!-- Test data -->
<local:TestDataForImage x:Key="MyTestData" />
<!-- Image for FallbackValue -->
<sys:String x:Key="ErrorImage">pack://application:,,,/NotFound.png</sys:String>
<!-- Image for NULL value -->
<sys:String x:Key="NullImage">pack://application:,,,/NullImage.png</sys:String>
</Window.Resources>
<Grid DataContext="{StaticResource MyTestData}">
<Image Name="ImageNull"
Width="100"
Height="100"
Source="{Binding Path=NullString, TargetNullValue={StaticResource NullImage}}" />
<Image Name="ImageNotFound"
Width="100"
Height="100"
Source="{Binding Path=NotFoundString, FallbackValue={StaticResource ErrorImage}}" />
</Grid>
See this links, for more information:
BindingBase.TargetNullValue Property
BindingBase.FallbackValue Property
Note: The upvoted and accepted answer does not answer the question; it explains how you can get {Binding A} to work if A is null, which is trivial to handle anyway, but it does not explain what happens and how to handle the much more interesting case of {Binding A.B} when A is null, and that is specifically what the question is asking. What follows is the answer to the question as stated.
WPF generally handles the case where A is null when you use A.B in a binding; I have not tried specifically with <Image Source>, but I have tried with <DataGrid ItemsSource> and with <Button Command>.
When WPF handles these cases, what I have observed happening is that there is no error or warning in the output window, and the application malfunctions a bit, but it does not crash:
In the case of <DataGrid ItemsSource>, the DataGrid appears empty.
In the case of a <Button Command>, the button is clickable, but when you click it nothing happens.
In the case of <Image Source> I would expect that no image will appear.
(Note that all these are cases of silent failure, so whoever decided that WPF should behave this way should be shot by firing squad at the central square with great celebrations and live music and big giveaways.)
The way we generally handle these cases depends on the nature of the element at hand.
For images, if an empty image is acceptable, then you do not need to do anything. If some image must be shown despite the property being null, then the accepted answer probably provides a solution.
For grids, not showing anything when the property is null is probably the desired behavior.
For buttons, the solution is to use an additional binding to the IsEnabled property of the button.
So, for example:
<Button Command="{Binding A.B}" IsEnabled="{Binding HasA}"/>
Where HasA is defined in the viewmodel as follows:
bool HasA => A != null;
first of all I would like to thank you for the many good posts that i read in this forum. Unluckily I could not find anything of help for my current problem (either here or anywhere else).
What I'm trying to do sounds quite simple, but I have no clue how to get it to work ... perhaps I'm still to new to wpf or I don't thing wpfy enough :)
I'm designing a front end for a part in an automated manufacturing:
I have a quantity of places where pallets can be put (but it can be empty as well).
Each pallet has up to 3 places where parts can be mounted
Everything is created dynamically of a database and is reacting to changes.
The position of the parts on the pallet comes from the database as well and should be visualized
What I would like to have is:
An overview over the pallet-places with a preview of the pallet
When I select a place I want to see a detail view of the place
When I click on a part on the pallet of the detailed pallet I want to see details to the part
The first two points are quite simple and work nicely:
I have got a DataTemplate for every component (part, pallet, pallet-place). Actually those are UserControls that are imported as Datatemplates
the overview is a ListBox with the places as DataContext
for the detail-place-view I use the UserControl and bound it to the SelectedItem of the Listbox
I tried to bind the Text of a Textblock to the ID of the selected Part ... and fail.
Probably I could use some global variables in the code behind - but that sound very ugly.
Can anybody help?
I have got a solution ... it is not nice but works.
I created an event in the pallet, that triggers, when the selected part-place changes
I handle the event in the pallet-place and create a new one
And finally I handle it in the overview and change the detailview accordingly
Most likely there are much nicer solutions, but it will suffice.
Perhaps try an ElementName binding?
<TextBlock Text="{Binding ElementName=Name_of_your_Listbox, Path=SelectedItem.ID" />
Can you post a bit more code of your TextBlock and your Binding?
Context is important, if i use a ContentControl and bind its content to the SelectedItem like this:
<ContentControl Content="{Binding SelectedItem, ElementName=mylistbox}">
I can bind to the ID of the selected item in the DataTemplate like this:
<ContentControl.ContentTemplate>
<DataTemplate>
<TextBlock Text="{Binding ID}" />
</DataTemplate>
</ContentControl.ContentTemplate>
That is because setting the Content of the ContentControl automatically sets the DataContext as well, and this binding is relative to the DataContext since no source (ElementName, RelativeSource, Source) has been specified.
I do not know how your UserControl handles the context, if the DataContext is not affected such bindings will not work. You would need to bind directly then:
<uc:MyDetailsView Data="{Binding SelectedItem, ElementName=mylistbox}">
<!-- ... -->
<TextBlock Text="{Binding SelectedItem.ID, ElementName=mylistbox}" />
This of course defeats the purpose of having the binding on the UserControl itself in the first place. But unless you post some relevant code it's quite hard to tell what is wrong.
Also check the Output window in VisualStudio, binding errors will show up there and might provide valuable information as to what went wrong.
This dialog makes no sense to me
http://img576.imageshack.us/img576/4223/50709706.gif
And I'm having trouble finding good tutorials on it. Most of the examples aren't detailed enough, or do stuff via code, but I'd like to take advantage of the IDE as much as possible.
Whats the difference between ItemsSource and DataContext?
I'd like to bind it to just a List for starters. I don't need SQL or databases or anything fancy. Where would I declare my list? In MainWindow.xaml.cs? How do I get it to appear in that dialog?
Think of "DataContext" as the default value for "Source" in a binding.
When you create a binding, you can specify the path and source, like this (I'll use TextBox as an example):
<TextBox Text="{Binding Path=Foo,Source={StaticResource Bar}}" />
So my TextBox.Text property is bound to a Foo property on an object called Bar (a resource somewhere in the application).
However, if you have a whole bunch of things that you want to bind to properties on Bar, it's easier to set Bar as the DataContext of the parent container. A Binding without a Source will just use the DataContext by default, and DataContext flows through to child controls from the parent. So:
<StackPanel DataContext="{StaticResource Bar}">
<TextBox Text="{Binding Path=Foo}" />
<TextBox Text="{Binding Path=Fizz}" />
<TextBox Text="{Binding Path=Buzz}" />
</StackPanel>
All of the TextBoxes are still binding to properties on Bar, but they're doing it without setting it as a Source explicitly.
So let's have another look at the dialog you posted. It's giving you several options for the "source" of the ItemsSource binding. When you choose "DataContext", you're telling Visual Studio that the ItemsControl doesn't need to know the source - it'll pick it up from the DataContext of the parent container (maybe even the Window itself).
If you chose one of the other options (ElementName, RelativeSource or StaticResource) then you'd be setting the binding's source explicitly for that ItemsControl.
Once you've told it that it's binding to the DataContext, you'll need to drop into the "Path" section of the dialog and tell it which property to bind the items of the control to. In the end, the markup would look something like this (assuming it's a ListBox):
<ListBox ItemsSource="{Binding Path=Foos}" />
So the items in the ListBox are coming from a property called "Foos", and that property is on an object that's set in the DataContext somewhere higher in the logical tree (perhaps on the Window itself).
You rarely need to use the data context of a control outside of the control. The most common use case for setting DataContext(DataContext = this;) is within UserControl's code-behind to make all controls within the UserControl to bind to the control's properties.
When you use a ListBox, setting ItemsSource is sufficient, unless you are doing something funky.
This is a pretty good walkthrough: http://windowsclient.net/learn/video.aspx?v=315275
Specifically, you need to set the DataContext first to tell it where to look for the ItemsSource. The easiest way is to set this on the Window through the XAML:
<Window.DataContext>
<controllers:DownloadManager />
</Window.DataContext>
I've got a TabItem contanining a listbox, which has an obeservable collection of my feeds class as its item source. When I refresh/load the feeds into the collection I want to disable the main window so that the user can't go clicking other things while this process is running. So I set tbCtrl.isEnabled=false; to my tab control on the form. Then assign an event handler to the a custom finish event which is triggered after all the feeds are loaded.
This all works fine, however the hyperlinks for the results which are currently displayed on the tab control never get re-enabled (Nor do the next few which are out of view due to the list box size). All the other results further down are fine, as are the results on the other tab.
I've tried calling InvalidateVisual on the tab control after everything is finished, to see if that makes a difference but that doesn't seem to cause any change.
I could understand it if it was all Hyperlinks doing it, or just the ones currently displayed, but I don't understand why ones which are out of scroll are not working either.
I hit the same issue.
What I did is to bind HyperLink's IsEnabled to the parent, and put that in an App global resource.
<Style TargetType="{x:Type Hyperlink}">
<Setter Property="IsEnabled" Value="{Binding IsEnabled, RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type FrameworkElement}}}" />
</Style>
I found the answer for my case of the hyperlink not getting re-enabled, not sure if it applies to yours:
I found that when the Hyperlink's parent control is disabled (IsEnabled=false), the Hyperlink will not get notified of changes, e.g. IsEnabledChanged does not get fired, even when the bound property changes value.
My solution was to change my Xaml to no longer disable the ancestor control (which was causing the Hyperlink's parent to be disabled). With the parent (TextBlock) always enabled, now Hyperlink updates properly always.
(I'm a little bothered that the IsEnabled binding behaves differently than Controls do, and I'm not sure what I would do if I couldn't leave the ancestor enabled... but at least this lets me understand the issue I was having, and lets me work around it.)
Details: WPF 3.5 SP1
It's not just HyperLinks. It seems to be more specifically TextBlock which of course is what you use to wrap a HyperLink in WPF. This will give the same issue :
<TextBlock>
<Run Text="Barcode:"/>
<InlineUIContainer BaselineAlignment="Center">
<TextBox Text="{Binding OriginalPackage.BarcodeNumber}" />
</InlineUIContainer>
</TextBlock>
I was hoping setting IsEnabled="True" would fix it but it doesn't seem to.
The easy solution is to use a StackPanel with Orientation="Horizontal"