Receiving Property Change Event like .net DataBinding

Question

3.00/5 (1 vote)

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Dear all
As you know it is very easy to use a ListControl like e.g. ComboBox with self developed classes.
We only have to supply a datasource which does support IList to the ComboBox and set some ComboBox’s properties:

C#

comboBoxGloss.DataSource    = anyting which supports IList;
comboBoxGloss.DisplayMember = "DisplayPropertyName";
comboBoxGloss.ValueMember   = "ValuePropertyName";

Last but not least to control the selected item we can simply add a DataBinding which binds ComboBox’s “SelectedValue” top a suitable property of our own class.

C#

comboBoxGloss.DataBindings.Add("SelectedValue", myClass, "MyValue");

class MyClass
{
  public int MyValue { get; set; }
}

=> So .NET hooks into the "set" method of myclass.MyValue and this in a way in which I do not have to support or pay attention to anything.

My question:
Can I hook in the same way like .NET’s DataBinding and implement my own “property change event sink”? And this without implementing anything in the “set” method of the respective property? Additionally I'm looking for a solution which is completely UI independed.

Sorry for my english, thanks in advance.
Regards

Posted 17-Jul-12 1:54am

idle63

Updated 17-Jul-12 1:56am

v2

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3 solutions

Solution 3

Now I found a way, but I'm not sure whether it is a clean solution (style, performance, ...). Of course I will encapsulate the example below in a class...later... perhaps.

Comments/warnings are welcome.
Regards

Some hours later:
It has side effects, respectively it does only work under some rare/unacceptable circumstances :(

It works only, if the “MyValue” property is bound to a ListControl.
It does only fire the change event if the ListControl does change “MyValue”
It does _not_ work if “MyValue” will be changed programmatically (myClass.MyValue= 2)

C#

// Nothing  special to implement, simply a class with a common auto property

class MyClass
{
  // For this property I like to install a "change listener"
  public int MyValue { get; set; }
}

C#

// Register an "change listener" to a property

class MyApplicationClass
{
  MyClass myClass= new MyClass();

  public MyApplicationClass()
  {
    // Add Listener to a specific object's property. In this case it is myClass.MyValue
    PropertyDescriptorCollection properties = TypeDescriptor.GetProperties(myClass);
    System.ComponentModel.PropertyDescriptor property = properties.Find("MyValue",
                                                                        false);
    property.AddValueChanged(myClass, new EventHandler(PropValueChanged)); 
  }

  private void PropValueChanged(object sender, EventArgs e)
  {
    // Here I will be informed about changes of MyClass.MyValue
  }
}

Posted 18-Jul-12 1:24am

idle63

Updated 18-Jul-12 6:29am

v3

Comments

BobJanova 18-Jul-12 10:29am

Oh that is nice, I didn't know that was possible.

[no name] 18-Jul-12 12:00pm

Maybe with a lot of side effects...but let's see, time will show it ;)
N.B: To come to this solution I downloaded the source code from .net and had a look inside how they do it.

Now I will test....

It has side effects, respectively it does only work under some rare/unacceptable circumstances :(

It works only, if the “MyValue” property is bound to a ListControl.
It does only fire the change event if the ListControl does change “MyValue”
It does _not_ work if “MyValue” will be changed programmatically (myClass.MyValue= 2)

All this I think is, because DataBinding relies on a form’s CurrencyManager (more or less)

Solution 1

comboBoxGloss.DataSource = anyting which supports IList;
comboBoxGloss.DisplayMember = "DisplayPropertyName";
comboBoxGloss.ValueMember = "ValuePropertyName";
comboBoxGloss.DataBind();

Posted 17-Jul-12 2:22am

endrum18

Comments

[no name] 17-Jul-12 8:53am

Sorry, I know how to bind a comboBox. I want to hook in into the event _like_ a combobox.
Regards

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BobJanova · Accepted Answer · 2012-07-17T04:22:00

Unfortunately the data binding mechanism is hooked quite deeply into controls, so you will have to implement something yourself. Fortunately, this is quite easy to do in the simple case (where you are binding to a simple property and the source supports INotifyPropertyChanged as the notification mechanism):

public class DataBinding : IDisposable {
 public INotifyPropertyChanged Source { get; private set; }
 public string SourceProperty { get; private set; }
 public object Target { get; private set; }
 public string TargetProperty { get; private set; }
 
 private PropertyInfo sourcePropertyInfo, targetPropertyInfo;

 public DataBinding(INotifyPropertyChanged source, string sourceProperty, object target, string targetProperty){
  Source = source; SourceProperty = sourceProperty;
  Target = target; TargetProperty = targetProperty;

  sourcePropertyInfo = source.GetType().GetProperty(sourceProperty);
  targetPropertyInfo = target.GetType().GetProperty(targetProperty);
 }

 public void Attach(){ 
  Detach(); // to stop double attachment
  source.PropertyChanged += SourceEventHandler;
  Refresh();
 }

 public void Detach() {
  source.PropertyChanged -= SourceEventHandler;
 }

 public void Dispose(){ Detach(); }

 private void SourceEventHandler(object sender, PropertyChangedEventArgs args){
  if(args.PropertyName == SourceProperty || args.PropertyName == null)
   Refresh();
 }

 public void Refresh(){
  targetPropertyInfo.SetValue(target, sourcePropertyInfo.GetValue(source));
 }

}

You can then use this in a way analogous to

var myBinding = new DataBinding(myClass, "MyValue", myComboBox, "SelectedValue");
myBinding.Attach();

... to bind anything to anything else.

You could also put the attachment code in the constructor, but that seems unnatural to me.

(Disclaimer: this is just typed into the posting box, so there might be minor mistakes.)