I have SL3 DataGrid and need a tooltip on rows and different columns which has data that needs to be fetched from DataBase when user hovers over the tooltip.
I saw samples around
that helps use the current binding context or the static content for the tooltip.
But, how can I get a usercontrol shown in the tooltip which goes and fetches Database only when user brings up the tooltip
Also, is there a way to easily fit this into MVVM instead of having a lot of code on the code behind?
I don't think tooltips properly leverage databinding, or at least in the way I think is proper. If you are binding to a ViewModel property in your XAML tool tip declaration that is going to resolve immediately, which means the call will be made immediately. I suppose you could plumb in some attached property or some other logic to list to the tool tip opening event, and then do an async web service call.
From an MVVM perspective, the VM probably should not care why something wants the data, just that it needs to lazy load it. So you could have a property on the VM (or perhaps even in the Model object) that exposes the data, but lazy-loads the data the first time the property is called. When the async call comes back you just fire the PropertyChanged event on your VM or M which should be interfaced with INotifyPropertyChanged. Then your databinding in the View will pick up the change. The key to getting all this to run when the pop-up of the tooltip occurs is to not bind the data until the tool tip actually does pop-up. It might be worth your time to extend the tooltip to do this, or right your own container to sit inside a tooltip that does this late-databinding.
Related
I'm developing a WPF/MVVM application and I have a listbox binding to data in a ViewModel. At various points I need the view model to cause the listbox to scroll to a given element.
How can I do this without creating a custom control and while still maintaining good separation of concerns?
I've currently got it working by creating a custom behavior class in the view layer with a dependency property VisibleIndex which the XAML code then binds to an integer in the view model:
<ListBox x:Name="myListBox"
local:ListBoxVisibilityBehavior.VisibleIndex="{Binding VisibleIndex}">
When the integer is set it triggers the dependency properties update handler which tells the listbox to scroll to the associated index.
This seems a bit hacky though because the dependency property value is never changed by the listbox and the update handler only gets called when the value changes, so the only way to ensure that the relevent item is visible is to do something like this:
// view-model code
this.VisibleIndex = -1;
this.VisibleIndex = 10;
The only reason I'm using a behaviour class at the moment is for binding my custom dependency property, is there a way to do something like this with events instead?
Attached properties are somewhat required in your case - as at some point, 'somewhere' you need to call the following method...
ListBox.ScrollIntoView(item)
or
ListBoxItem.BringIntoView();
And for that you need some sort of code behind - and attached properties/behaviors are a nice way of packaging that, w/o impacting your MVVM.
Having said that - if you just need to have your 'selected item' scrolled into view at all times (which is the case most of the time). Then you could use a different attached-property based solution (that again):
mvvm how to make a list view auto scroll to a new Item in a list view
All you have to do then is to set or bind to SelectedItem.
That's a bit 'nicer' if you wish - but the mechanism is the same.
For anyone else interested in the answer to this one of the MS engineers on the WPF forum cleared it up for me. Instead of binding to an event directly you bind to a wrapper object that encapsulates that event. The behaviour can then grab the reference to the wrapper from its DP and do whatever it wants with it i.e. subscribe to the event, trigger it etc.
I'm trying to build a maintenance form in WPF, using Telerik's WPF controls. The idea is to have a grid and a form that are bound to the same collection. Changes to the grid should be immediately reflected in the form, and vice versa. An online example using Telerik's Silverlight controls is here.
My specific problem is that when I enter a new record (by clicking on the "Add" icon in the upper-right of the DataForm), the record is added to both the grid and to the form's collection, but it seems to break the synchronization. The new row in the grid stays highlighted, like the grid thinks it's not done being edited, and while changes to the current record in the form are reflected in the grid, changes to the current record in the grid are no longer being reflected in the form.
But my real problem is more general than that. WPF controls, like Telerik's, are heavily dependent on binding, and in having what they bind to support specific behaviors. In this case, the underlying record needs to support INotifyIEditableObject, so that when the user hits the Cancel button on the form, the EditCancel method on the record can be called. Which is then responsible for setting its properties back to what they had been, and then raising a NotifyPropertyChanged event, so that controls that are informed that they have been so set.
When I didn't have EditCancel working right, I would hit cancel on the form and the values in the grid would not be changed. My guess as to what is going on with the inserts is that something in either my collection or by records doesn't support whatever it is that makes this work. The grid doesn't know that the form has finished editing the record because either my record or the collection hasn't told it.
And here's the real question: how can I find out what these third-party controls are expecting? Telerik's RadGrid can be bound to pretty much anything that can be IEnumerated. But all this neat enhanced functionality depends upon being bound to collections that are very much more specific. I don't get errors, when I bind to a collection that lacks facilities that are needed for certain functions to work, I just get a control that doesn't work.
How can I tell, when working with someone else's control, for which I do not have source code, what functionality it requires, in the objects it binds to?
Your best bet would be to browse Telerik's documentation or ask on their support forums
If that doesn't work, I like to use Snoop for debugging WPF's Visual Tree and Reflector for looking through compiled libraries
I have a view that containing a user control.
I want to make the view model to notify the user control to do some action (refresh its' data).
I can pace some bool property in my VM and bind it to the user control so it will trigger it, but I think it's a little abuse of the property.
I feel I missing something, and can't find a solution. I will appreciate any comment.
My solution:
I'm going to solve the problem by registering an event of collection changed in my UserControl, since I'm binding to that control a view of a collection thru CollectionViewSource.
My original problem was how to make a chart control inside the UserControl to get updated when I filtering the data source. After the filtering operation from the VM, an event will raise and I will make the chart to get refresh either in the UserContol's code behind
Since you've indicated MVVM tag solution would be pretty straightforward - just bind control to a data by exposing data items/whatever by ViewModel so any data updates would be automatically dispatched to View via bndings if you would provide INotifyPropertyChanged / INotifyCollectionChanged by a ViewModel.
If you've bound your UserControl correctly, you shouldn't need to manually refresh the data since WPF will automatically update the UI when INotifiyPropertyChanged triggers
That said, if you wish to send a message from the ViewModel to the View, I usually use an messaging system of some kind to keep the Views and ViewModels separate. The two I've used and would recommend are MVVM Light's Messenger, or Microsoft Prism's EventAggregator
Either system will allow your ViewModel to broadcast a message, and your View can subscribe to receive these messages and handle them as needed.
I'm working in a WPF project, I'm using the MVVM patter in my project.
I created a user control (also in WPF) and I want to use it in my project, now, my problem is that I have a method in my user control that I need to call from my View Model, but I don't know how to do that, how to bind to the method inside my control from the view model.
If I use code behind, obviously there is no problem since I have a direct reference to my control, so I can do "mycontrol.MyMethod();"m, but of course, doing in this way will go against the logic of the MVVM pattern.
I tried to use a Dependency Property in my user control, and use that Dependency Property to bind to it in the xaml of my project but it didn't worked, the compiler says that the property was not found or is not serializable.
So I will appreciate if someone can share some light about how can I accomplish this.
Edited
As far as I understand you have the view, which is all the GUI, then you have the model, which is all the logic, and them you have the view-model which is like an intermediate layer used to bind the view with the model, right?
In this way I have developed my project, however I came to the problem that I need a custom control, a TextBox that remember what the user entered, and when he start typing, if there are words that start with that letter, those words are shown as a suggestion, as Google does it.
This TextBox is used as a search filter; so I created a user control to do this, I added a method to my user control to allow whatever application that uses my control to add items to an internal array that holds all the strings that the user has entered.
I created a user control because I couldn't find any control that behaves the way I want.
So my problem is when I add my user control to the main project, because I need to someway be able to call the method that add the items to the internal array, but maybe I'm doing things the wrong way, so if any of you has a better idea, I will appreciate if you shared it with me.
You should never call View methods from ViewModel, and vice versa.
Make a property (ObservableCollection?) on your ViewModel, it will have CollectionChanged event, subscribe to it to monitor changes (if needed).
When you add an item to the collection in your ViewModel, GUI will be updated accordingly (you have to perform the Add() operation on GUI thread, btw).
If you need to change the current position in your list, there are colections for that (CollectionViewSource, etc).
If you really really need to pass a string to your control, make a DependencyProperty and bind it OneWay to your ViewModel's property. When you set the value, it will call PropertyChangedCallback on your DependencyProperty.
Why does the consumer of the user control need to maintain the control's internal array? That seems like you've exposed an implementation detail that you don't need to.
Why not simply make that array a dependency property (and an IEnumerable<string> or ObservableCollection<string> besides)? Then you can simply create the corresponding property in your view model and bind it to the control. It also makes the control considerably more versatile.
You shouldn't call something in the View from the ViewModel since that breaks the model.
If the reason you want to call the method in the user control is to do with UI only, I don't see anything wrong with doing it from the view - the view's cs and the view's xaml are in the same "space" in the model. You can be overly-purist in wanting to have lean and mean view cs files.
I am very new to WPF, and I have a very basic WPF question:
Suppose we have a custom dll with some business logic that fires events such as
ModemIsConnected. On the UI side (.xaml) there is a label that changes its value to OK once that event is fired. I would like to offload the event handling portion (changing label's status and other minor UI tweaks) to a designer. Is it possible to handle events in xaml without creating code-behind?
Thanks!
The simple answer is I don't believe it's possible. There are no doubt things you can do with data binding and the like, but then you're getting beyond the kind of thing you want a designer to be doing.
A couple of options:
Teach the designer the bare minimum of coding an event handler and calling a storyboard. With intellisense and the nice interaction between Blend / Visual Studio you could have someone up and running fairly quickly.
Have them create storyboard animations for any of the 'minor UI tweaks' you require, and then you can hook these up to the event and change your label text with only 3-5 lines of code.
You can have the designer do the UI side without them having to get their hands dirty with code. You could create a class that implements IPropertyNotifyChanged with a boolean property that changes as the modem state changes. The designer can then bind to that property and do fancy triggers, state changes etc etc from within the XAML and the binding system will handle "telling" the UI the value has changed.