How to change a property when another property is changed in MVVM - wpf

Question

I am using WPF and MVVM for a project. I have a view with a GridView control. User can Insert/Update/Delete In Grid View. when any of the action happen changes reflect in ViewModel. This part is working Ok. But when I want to save the changes in Database I need to loop through each Item in ItemSource one by one. which takes the extra time to complete. I want to process only those Items which are changes.
To accomplish this , I add a boolean property in my Model to indicate whether the Item is changed or note. But problem is that I can not see any way to set this boolean property whenever any other property is changed.
Can any body help me how to do it?
EDIT
I have a SelectedItem Property , and I am assuming that whenever an Item is selected in GridView , User will update or insert the row. so on SelectedItem property I have set boolean property of SelectedItem to True. and while looping to save records I am saving all those records who have True in their boolean property. I know its not the perfact way, but right now I do not have any other way to do it. Your thoughts?

Answer 1

You could subscribe to the PropertyChanged event on your Model and set the Flag to True.
But keep in mind that you have to set the Flag to false after you loaded the data from the database, because the initialization of the model will also call the propertychanged event.
Example for class with IsDirty-Flag:
public class Sample : INotifyPropertyChanged
{
private int id;
private string name;
private bool isDirty;
public event PropertyChangedEventHandler PropertyChanged;
public int Id
{
get { return id; }
set
{
if(id != value)
{
id = value;
RaisePropertyChanged("Id");
}
}
}
public string Name
{
get { return name; }
set
{
if (name != value)
{
name = value;
RaisePropertyChanged("Name");
}
}
}
public bool IsDirty
{
get { return isDirty; }
set
{
if (isDirty != value)
{
isDirty = value;
RaisePropertyChanged("IsDirty");
}
}
}
protected virtual void RaisePropertyChanged(string propertyName)
{
if (propertyName != "IsDirty")
{
IsDirty = true;
}
var handler = PropertyChanged;
if (handler != null)
{
handler(this, new PropertyChangedEventArgs(propertyName));
}
}
}
if you are using an ObservableCollection, you can also add an eventhandler to track the rows that are newly added or deleted

Answer 2

If you use MVVM you should have implementation of INotifyPropertyChanged. And you can add some logic to set up yours boolean property in OnPropertyChanged handler.

Answer 3

If you are willing to take a dependency on a build time tool you can do this with ILWeaving.
So if you combine Fody with the PropertyChanged addin then IsDirty functionality is supported out of the box.
Then Martins example can be simplified to this
public class Sample : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
public int Id { get; set; }
public string Name { get; set; }
public bool IsChanged { get; set; }
}
Note the use if IsChanged instead of IsDirty.
And then this will exist in the compiled assembly
public class Sample : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
public virtual void OnPropertyChanged(string propertyName)
{
var propertyChanged = PropertyChanged;
if (propertyChanged != null)
{
propertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
}
int id;
public int Id
{
get { return id; }
set
{
if (id != value)
{
id = value;
IsChanged = true;
OnPropertyChanged("Id");
}
}
}
bool isChanged;
public bool IsChanged
{
get { return isChanged; }
set
{
if (isChanged != value)
{
isChanged = value;
OnPropertyChanged("IsChanged");
}
}
}
string name;
public string Name
{
get { return name; }
set
{
if (!string.Equals(name, value, StringComparison.Ordinal))
{
name = value;
IsChanged = true;
OnPropertyChanged("Name");
}
}
}
}