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HOw do I put "Set breakpoints in the getters for the bound properties" ?
I ask because at present I am not using field properties as in get or set...
So not sure where you mean to place breakpoint.
Thanks
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When you read the values out of the database, where do you put them? There must be some piece of code that contains these properties. Put the breakpoints on the code that populates these properties - this is debugging 101; you need to learn this stuff rather than coming here and asking us to solve this without sight of your code.
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This kind of debugging is what I have done already but have not spotted where the error is. I will continue again.
Thanks
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Well, you have bound the controls to the Notes and EnglishNotes properties of some Class. Therefore, you need to set the breakpoint in the setter for these properties. Then when these properties get updated, you can check whether the expected values for these properties are being set. This sounds like a classic case of two properties getting set to the same value like this
foreach (DataRow dr in ds.Tables[0].Rows)
{
MyClass.property2 = dr.IsNull(2) ? String.Empty : (string)dr.ItemArray[3];
MyClass.property3 = dr.IsNull(3) ? String.Empty : (string)dr.ItemArray[3];
}
instead of
foreach (DataRow dr in ds.Tables[0].Rows)
{
MyClass.property2 = dr.IsNull(2) ? String.Empty : (string)dr.ItemArray[2];
MyClass.property3 = dr.IsNull(3) ? String.Empty : (string)dr.ItemArray[3];
}
...and I have extensive experience writing computer code, including OIC, BTW, BRB, IMHO, LMAO, ROFL, TTYL.....
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Notes and EnglishNotes need to be properties for the binding to work properly.
public string Notes;
private string _notes;
public string Notes { get { return _notes; } set { _notes = value; } }
public string Notes { get; set; }
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Your xaml code looks ok.
Try and have a look at the place where you are populating the model and make sure right values are being passed into the model attributes.
The funniest thing about this particular signature is that by the time you realise it doesn't say anything it's too late to stop reading it.
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Hi,
I have Question about the use of Observable Collection? During reading about MVVM Pattern i read about the observable collection that it reflect the changes to the UI Automatically which is not possible in the List collection.But i really dont understand it what it exactly means in practical terms. I want a demo for the Difference between the List VS ObservableCollection Vs PropertyChangedEventHandler. I have read the document on your site but i am yet not clear about it? will you please help me?
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The ObservableCollection implements the INotifyCollectionChanged interface, so it fires a CollectionChanged event whenever an element is added, removed, replaced, or moved.
The binding system knows how to react to objects that implement INotifyCollectionChanged and INotifyPropertyChanged... So when you bind to one of those, the binding system hooks the event and updates itself when it gets notified of a change.
The List class doesn't implement that interface.
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Can u please explain me how the changes to the _studentList can reflect to UI with code?
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I just explained it. The ObservableCollection fires a CollectionChanged event. The data binding system handles that event and triggers an update. That's it.
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Sorry, but i am not getting what exactly i want.
Actually I am new to silverlight so i am not clear with it.
In the Given code (Populating a DataGrid in a Silverlight Application using MVVM)
it is not calling the PropertyChanged Event. Can u provide code which calls that event.
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CollectionChanged, not PropertyChanged...
The ObservableCollection class fires the CollectionChanged event internally, whenever you add/remove/replace/move items.
The data binding system handles this event.
All of this happens inside the framework... You won't see the code for it... It's automatic.
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There are two parts to binding that you are concerned with here. The first, as you are aware, is the use of ObservableCollection. This tells you that the collection has changed; in other words that items have been added or deleted in the collection. This does not tell you that an individual item has changed.
To capture notifications that an individual item has changed, you need to implement INotifyPropertyChanged in the class (or an ancestor of). Simplistically, when an item changes, the PropertyChanged event fires, and this tells the binding engine that an item needs to be updated in the UI. If you look at samples, you'll typically see a class called something like ViewModelBase. This class is the one that implements the property changed notification, saving you from having to update the code in lots and lots of locations. Here's a typical example of this class:
public abstract class ViewModelBase : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
protected virtual void OnChanged(string property)
{
var handler = PropertyChanged;
if (handler == null)
{
return;
}
handler(this, new PropertyChangedEventArgs(property));
}
}Now, you'll derive from this class and call OnChanged in your property setters. This would typically look something like this:
private string _passCode;
public string PassCode
{
get { return _passCode; }
set
{
if (_passCode == value) return;
_passCode = value;
OnChanged("PassCode");
}
}When the user changes a value in PassCode, the value is updated and then the change notification is raised which tells the binder to update only that named field (if you want to update all fields, you pass an empty string to OnChanged). There are a couple of things to note here - always test to see if the update value is the same as the value you already store, this prevents you updating something that hasn't changed; the name of the property that is raised must match the name of the property, so calling "Pa4sCode" would fail to update the value as it's not the name of the property (PassCode).
I hope that this makes sense to you. All too often people fall into the trap of assuming that ObservableCollection covers both sides. It's an easy mistake to make.
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Hi,
Thanks.
I understaqnd it now.
I am new to Silverlight. But i am working on the project which is based on silverlight. This project is completed but i am trying to understand this.
Would you please suggest me some resources to learn silverlight as early as possible (Books ,Sights, etc.).
Thanks
Umesh Tayade
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There are plenty of blogs about Silverlight, and several CPians maintain SL blogs. Probably the premier SL site though, is Jesse Liberty's site[^]. As far as books go, I'd recommend Laurent Bugnion's excellent Silverlight 4 Unleashed[^].
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Hi Developer,
I am using one select All Button to select all row in Datgrid (CheckBox selection).
So how to Check CheckBox in Datagrid.
Regards
Nanda.
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In the collection that you are binding to, you have a collection of items. Each item is an instance of an object that represents a single row. Add a property to this that represents whether or not it has been checked, make it raise the PropertyChanged event and bind your Checked to this. Finally, when the user clicks select all, simply iterate over the collection and set the checked property to true. With the wonder of data binding, the UI will also update.
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Hi,
In my application, the user has to navigate through RadioButton's group using the keyboard
By default, the arrow keys are used to navigate and the space bar used to select the radio button.
I would like the 'select' key to be another keyboard key!
How should I please process to switch the key used for the button selection by the "A" key, for instance?
Thank you for any kind help!
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You mean add a underscore (_) to the content?
If you do "Radio Button #_1", the 1 will be underlined and a user can hit Alt+1 to select the radio button.
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Thanks for your reply!
No, that's not what I mean (sorry english isn't my mothertongue)
I mean, being able to select the radio button which has the focus, with the key "A" instead of the default "SPACE" key!
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A quick and dirty way would be to use your own RadioButton-derived class that responds to the key press you want, something like:
public class MyRadioButton : RadioButton
{
protected override void OnKeyDown(KeyEventArgs e)
{
if (e.Key == Key.A)
OnClick();
else
base.OnKeyDown(e);
}
}
Mark Salsbery
Microsoft MVP - Visual C++
![Java | [Coffee]](https://codeproject.global.ssl.fastly.net/script/Forums/Images/coffee.gif)
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Dear All,
In my application i am using WPF data grid from wpftoolkit. Here in order to achieve one of my requirement i am about to find the parent of the data grid cell.
in my grid i am having an image in an template column.
<my:DataGridTemplateColumn Width="30" >
<my:DataGridTemplateColumn.CellTemplate>
<DataTemplate>
<Image Name="imgCalendar" ToolTip="Select" Source="calendar2.jpg" Stretch="Fill" PreviewMouseUp="imgCalendar_PreviewMouseUp"></Image>
</DataTemplate>
</my:DataGridTemplateColumn.CellTemplate>
</my:DataGridTemplateColumn>
below is the imgCalendar_PreviewMouseUp event.
Microsoft.Windows.Controls.DataGridCell cell = sender as Microsoft.Windows.Controls.DataGridCell;
Microsoft.Windows.Controls.DataGrid dataGrid = FindVisualParent<Microsoft.Windows.Controls.DataGrid>(cell);
static T FindVisualParent<T>(UIElement element) where T : UIElement
{
UIElement parent = element;
while (parent != null)
{
T correctlyTyped = parent as T;
if (correctlyTyped != null)
return correctlyTyped;
parent = VisualTreeHelper.GetParent(parent) as UIElement;
}
return null;
}
So this is my code.
Now here when ever the grid fills , when i click the image for the first time i am not getting the parent.
But when i click once(i.e for the second time) i am getting the datagrid as parent. I don't know why its happening like this.
Please help me and thanks in advance.
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The sender is an Image, right? So shouldn't that be something like this...
private void imgCalendar_PreviewMouseUp(object sender, MouseButtonEventArgs e)
{
Microsoft.Windows.Controls.DataGridCell cell = FindVisualParent<Microsoft.Windows.Controls.DataGridCell>(sender as Image);
Microsoft.Windows.Controls.DataGrid dataGrid = FindVisualParent<Microsoft.Windows.Controls.DataGrid>(cell);
}
If you just set the Name property on the DataGrid then you already have a DataGrid member variable of that name so I'm not sure why you need to do any of that to get a DataGrid reference... 
Mark Salsbery
Microsoft MVP - Visual C++
modified on Tuesday, May 10, 2011 4:59 PM
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Thanks Mark for your time and for reply.
I will check the method mentioned here.But the thing is same code is working on other window with the same data grid. I dont know why here.
I will try and get back to you.
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I didn't just post a guess
I copied your code into Visual Studio and ran it in debugger and immediately saw your "sender as Microsoft.Windows.Controls.DataGridCell" return NULL.
Commented out that line and changed it to what I showed and it worked fine.
Maybe the other window that works has different code?
And why are you trying to find the DataGrid this way when you already have access to the DataGrid?
Mark Salsbery
Microsoft MVP - Visual C++
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