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Errm. Are you 100% sure about this design approach as an absolute? How do you handle validation in this case or support for IEditableObject? The reality is, a hybrid approach will generally be necessary.
In the case where you want to simply forward a property on, then your approach is fine, but where you need to validate something before it can be committed, then you should use an intermediary value. Similarly, if changes can be rolled back then you should support an intermediary value. That's the approach to use.
Take the case you mentioned - where you have a huge amount of text in a model, the VM would generally do some clever processing so that only a subset of the text was kept bound to the view, virtualized in other words, and the model would be updated with the subset. In this way, the VM simply presents a snapshot of some of the text at that point in time.
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The model should often times encapsulate all this functionality so it can be reused. Validation isn't an issue. You can handle that in the setter, or more appropriately have the model implement IDataErrorInfo.
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Basically, with this approach, you have virtually completely defeated the whole purpose of MVVM. The point of putting this into the VM is that it is appropriate for the View and the ViewModel to interact, but you are delegating responsibility to the Model. What's the point of the VM anymore with this - it's purely acting to relay data in your approach. It's no longer adding any value.
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I get your point, and agree to a certain extent, but also disagree to a certain extent  .
Do you agree that the model should implement INPC? or do you believe that duty falls to the VM and that the model should just be a simple POCO? I think thats the models job. Why duplicate INPC code in every single VM that uses the model? If the model is already implementing INPC (and INCC), how is that any different from it implementing IEditableObject and IDataErrorInfo?
I am not saying the model should handle everything, it most certainly should not. It should however encapsulate everything to do with an object so the code is centralized and not C&P'ed everywhere.
The VM still has plenty to do: commands, occasional repacking of data, exposing non-model related properties, etc. The model doesn't really expose anything GUI related, thats the VMs job.
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That's fair enough. We do agree here then. My opinion was not that the VM should reimplement everything the model can do, just that there were certain occasions when it has to do extra work so you have to take it on a case by case basis.
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I don't think you have a misunderstanding either, FWIW.
There are different ways of doing things - and no one way is intrinsically 'the right way'
I tend to get my Model object, use it to create a ViewData object (which I use inside the ViewModel) and don't persist the Model object.
I use a specific user-controlled option to update my repository - which creates a new Model from the ViewData
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Hmm.
I would say that your business level entities coming from your data layer have no business at all in your GUI layer.
It seems as if you do not have a layered application and that is your first problem.
At the minimum, I'ld say a GUI layer, business layer and data layer is essential.
Your mvvm pattern is found in your GUI layer and deals exclusively with GUI stuff.
Use dto's to send data from and to your business.
Your project will look like a bowl of spaghetti if you don't structure it properly.
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I guess people are relucent to publish low-brow MVVM examples in fear of getting shot down in flames.
The way I do it (using Entity Framwork) is the ViewModel provides a SaveCommand which the View binds to. After all, it should be up to the user to determine if the data is saved. So when the user clicks the Save button or other events occur, the command is fired and a method can handle the logic to persist the changes back to model.
In EF it's a one liner myContext.SaveChanges();
In your situation it sounds like you'll need to do a bit more leg work. But the stategy should still work. You need to catch the event in the ViewModel using a command.
"You get that on the big jobs."
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I take option 2 over option 1 'almost always'
I treat my Model object as an object whose job it is to go get the data for the client. Once delivered its job is done, so I don't keep a reference to the Model in my ViewModel (again, 'usually' )
So I rarely Update model objects - as they're going to be persisted back in the DB - I create new objects when required and send them back to be stored.
I must confess to not quite understanding your scenario here - how your report and Parameter objects interract - but assuming you are maintaining the report and/or parameter objects, then I would normally have some sort of Apply method as per your option2.
if you do it this way, then at least you have the option of using the Apply method as frequently or infrequently as you want to - on a timer, every time a parameter type is changed - whatever.
But I don't think there's a 'right' way of doing it - and it depends on your exact requirements.
One of the downsides of option 1 is the ability to revert changes quickly... As you're maintaining a reference to the Model and want to cancel changes, you can just re-set your VM from the Model and you're back!
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How do we change themes dynamically, if themes are stored into a DLL?
Generally, if theme is in form of .xaml file, we write in xaml
<ResourceDictionary Source="Themes/ShinyRed.xaml"/>
And in CS:
ResourceDictionary skin = new ResourceDictionary();
skin.Source = new Uri(@"Themes/ShinyRed.xaml", UriKind.Relative);
Window win = Window.GetWindow(this);
win.Resources.MergedDictionaries.Clear();
win.Resources.MergedDictionaries.Add(skin);
where 'Themes' is folder name and 'ShinyRed.xaml' is theme name.
Now, if theme is in form of DLL file, we write in xaml
<ResourceDictionary Source="/ThemeDll;component/ShinyBlue.xaml"/>
where 'ThemeDll' is the name of DLL, and ShinyBlue.xaml is theme name.
How to get same result at run-time?
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I think you can get the result same way as you do it with normal xaml file
in CS:
ResourceDictionary skin = new ResourceDictionary();
Instead of
skin.Source = new Uri(@"Themes/ShinyRed.xaml", UriKind.Relative);
Use this
skin.Source = new Uri(@"/ThemeDll;component/ShinyBlue.xaml", UriKind.Relative);
Window win = Window.GetWindow(this);
win.Resources.MergedDictionaries.Clear();
win.Resources.MergedDictionaries.Add(skin);
it works fine for me.
I hope i got your question correctly.
Work relieves us from three great evils, boredom, vice, and want.
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Thanks! 
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Well, I have been trying to figure this one out for three days straight and I still haven't come up with a fix.
Basically I am trying to swap out the clicked Ellipse with the only empty spot on the 3x3 checkerboard. 8 of the 9 squares are occupied. I need to find the one spot that is not occupied and I can't seem to do it. Why? Because even though there is an empty spot on the grid at runtime, Javascript refuses to acknowledge this. I used the line: var childrenCount = canvasArray[i].children.count; .. so that's all the canvases. If at runtime there is an empty spot, then how come my code refuses to see it? Or am I not writing the right code? How is the empty spot represented and found at runtime? That's what I want to know.
Here is the pseudocode:
if (squareOnGrid is empty) {
log.write(squareOnGrid + ' is empty');
emptySquare = squareOnGrid;
oldPositionBorder = sender;
oldPositionR = checkerPiece.row;
oldPositionC = checkerPiece.col;
checkerPiece.row = empty.row;
checkerPiece.column = squareOnGrid.column;
oldPositionBorder = null;
}
I want to do this with Javascript (not C#).
I already have this (Javascript):
<br />
function switchPlaces(sender) {<br />
<br />
for (var i = 0; i < canvasArray.length; i++) {<br />
var oldLocationBorderParent = sender;<br />
var oldLocationCanvasParent = oldLocationBorderParent.findName('canvas' + (i + 1));<br />
var oldLocationChild = oldLocationCanvasParent.findName('ellipse' + (i + 1));<br />
<br />
var childrenCount = canvasArray[i].children.count;<br />
log.info(childrenCount);
<br />
if (childrenCount == 0) {<br />
log.info(canvasArray[i] + ' has no children');<br />
var emptySpot = canvasArray[i];<br />
sender['Grid.Row'] = emptySpot['Grid.Row'];<br />
sender['Grid.Column'] = emptySpot['Grid.Column'];<br />
oldLocationCanvasParent.children.remove(oldLocationChild);<br />
}<br />
}<br />
}<br />
Here is my Silverlight code:
<br />
<Grid<br />
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"<br />
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"<br />
Loaded="onLoaded" ShowGridLines="True" Background="CornflowerBlue"><br />
<br />
<Grid.ColumnDefinitions><br />
<ColumnDefinition Width="100"/><br />
<ColumnDefinition Width="100"/><br />
<ColumnDefinition Width="100"/><br />
<ColumnDefinition/><br />
</Grid.ColumnDefinitions><br />
<br />
<Grid.RowDefinitions><br />
<RowDefinition Height="100"/><br />
<RowDefinition Height="100"/><br />
<RowDefinition Height="100"/><br />
</Grid.RowDefinitions><br />
<br />
<Border Grid.Row="0" Grid.Column="0" x:Name="b1" MouseLeftButtonUp="switchPlaces" ><br />
<Canvas x:Name="canvas1"><br />
<Ellipse Width="100" Height="100" x:Name="ellipse1" Fill="Red" Visibility="Visible"/><br />
</Canvas><br />
</Border><br />
<br />
<Border Grid.Column="0" Grid.Row="1" x:Name="b2" MouseLeftButtonUp="switchPlaces" ><br />
<Canvas x:Name="canvas2"><br />
<Ellipse Width="100" Height="100" x:Name="ellipse2" Visibility="Visible"/><br />
</Canvas><br />
</Border><br />
<br />
<Border Grid.Column="0" Grid.Row="2" x:Name="b3" MouseLeftButtonUp="switchPlaces" ><br />
<Canvas x:Name="canvas3"><br />
<Ellipse Width="100" Height="100" x:Name="ellipse3" Visibility="Visible"/><br />
</Canvas><br />
</Border><br />
<br />
<Border Grid.Column="1" Grid.Row="1" x:Name="b4" MouseLeftButtonUp="switchPlaces" ><br />
<Canvas x:Name="canvas4"><br />
<Ellipse Width="100" Height="100" x:Name="ellipse4" Visibility="Visible"/><br />
</Canvas><br />
</Border><br />
<br />
<Border Grid.Column="1" Grid.Row="2" x:Name="b5" MouseLeftButtonUp="switchPlaces" ><br />
<Canvas x:Name="canvas5"><br />
<Ellipse Width="100" Height="100" x:Name="ellipse5" Visibility="Visible"/><br />
</Canvas><br />
</Border><br />
<br />
<Border Grid.Column="2" Grid.Row="0" x:Name="b6" MouseLeftButtonUp="switchPlaces" ><br />
<Canvas x:Name="canvas6"><br />
<Ellipse Width="100" Height="100" x:Name="ellipse6" Visibility="Visible"/><br />
</Canvas><br />
</Border><br />
<br />
<Border Grid.Column="2" Grid.Row="1" x:Name="b7" MouseLeftButtonUp="switchPlaces" ><br />
<Canvas x:Name="canvas7"><br />
<Ellipse Width="100" Height="100" x:Name="ellipse7" Visibility="Visible"/><br />
</Canvas><br />
</Border><br />
<br />
<Border Grid.Column="2" Grid.Row="2" x:Name="b8" MouseLeftButtonUp="switchPlaces" ><br />
<Canvas x:Name="canvas8"><br />
<Ellipse Width="100" Height="100" x:Name="ellipse8" Visibility="Visible"/><br />
</Canvas><br />
</Border><br />
<br />
</Grid><br />
If anyone has any idea how to fix this..
Thank you
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I must be missing something here...
What is this canvas array and how does it relate to the Silverlight Grid?
How does the managed Silverlight code know about the canvas array?
How are you calling javascript from managed code?
Mark Salsbery
Microsoft MVP - Visual C++
![Java | [Coffee]](https://codeproject.global.ssl.fastly.net/script/Forums/Images/coffee.gif)
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Hi,
my question is, how do I sort related items of an entity.
In an invoice editing window, I have one ComboBox displaying all customers:
XAML:
<UserControl.Resources>
<CollectionViewSource x:Key="cvsCustomers"
d:DesignSource="{d:DesignInstance local:Customer, CreateList=True}" />
...
</UserControl.Resources>
<ComboBox ItemsSource="{Binding Source={StaticResource cvsCustomers}}" .../>
Code-behind:
Dim cvsCustomers As System.Windows.Data.CollectionViewSource
cvsCustomers = CType(Me.FindResource("cvsCustomers"), System.Windows.Data.CollectionViewSource)
Dim qryCustomers = _
From c In myEntities.Customers _
Order By c.CustomerCode
Select c
cvsCustomers.Source = qryCustomers
Now I have a 2nd ComboBox displaying all contact persons of the selected customer. This works fine, but the entries in this second ComboBox are unsorted / sorted by ID.
XAML:
<ComboBox ItemsSource="{Binding Path=myInvoice.Customer.Contacts}" .../>;
How do I get the list on the 2nd ComboBox sorted?
King regards,
and thanks in advance for tips/suggestions,
Nico
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Hey,
I've been optimising a piece of software with a very large number of simple controls (~30000), most of whom have their parent panel virtualised at any one time (reducing the number in the visual tree to a few hundred). Running through ANTS profiler, I'm told that 60-70% of CPU-time is taken up by UIElement_CreateAutomationPeerDelegate.Invoke and its child methods. A user interacting with the program for 20 seconds or so [creating an additional ~20 of these controls, deleting a few, and moving a few around the page] results in this method being called 5.4 million times. Putting a counter near this method confirms this when run without debugging/ANTS.
As far as I'm aware, I haven't touched AutomationPeer-related methods, and it is used for Accessibility/COM stuff. Can I turn this 'function' off, or are there ways of reducing how many times it is called?
TIA,
Lee
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At the risk of getting 1'ed, I'd say you are trying to band aid things here. Fix the real issue. You shouldn't need 30,000 controls in a single window .
-- Modified Monday, July 18, 2011 7:04 PM
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Haha, well agreed to an extent. The maximum number of controls 'on' the window at any one time is actually around 200 (and usually only around 40) - the rest are held in memory waiting to be connected to the visual tree when scrolling takes place.
I have tried virtualising these 'properly' so that they are re-used but the overhead for them binding to their data is actually more costly than having them just sit in memory (which I certainly found surprising)
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Hi,
is their any timepicker control available in wpf with vb.net?
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I am looking for a way where a control can be enable when an item from a combo box is selected. Is there a simple way through data binding when a user selects an item from a combo box that it then enables another control to be used?
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One way is to bind IsEnabled on the control(s) to the ComboBox SelectedIndex or SelectedItem property using a value converter[^] on the binding to convert the Selectedxxx value to a bool.
[System.Windows.Data.ValueConversion(typeof(int), typeof(bool))]
public class SelectedIndexToIsEnabledConverter : System.Windows.Data.IValueConverter
{
public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
return ((int)value >= 0) ? true : false;
}
public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
throw new System.NotImplementedException();
}
}
<UserControl.Resources >
<local:SelectedIndexToIsEnabledConverter x:Key="SelectedIndexToIsEnabledConverter" />
</UserControl.Resources>
...
Example binding:
IsEnabled="{Binding Path=SelectedIndex,ElementName=comboBox1,Converter={StaticResource SelectedIndexToIsEnabledConverter},Mode=OneWay}"
Mark Salsbery
Microsoft MVP - Visual C++
modified on Friday, July 15, 2011 12:33 PM
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Hello,
Could someone help me out here please.. I have a game algorithm problem: http://oi56.tinypic.com/29x6op0.jpg
Thank you
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Please post on the algorithm board[^] if you want algorithms.
Mark Salsbery
Microsoft MVP - Visual C++
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