Library code snippets
Complex Data Binding
Introduction
Data binding can be nasty - especially when you cant use the System.Data objects. I have tried to use all the features of databinding to show you. It is pretty small but takes a hell of a long way to get there..
The sample shows a custom collection with objects in it having properties, some of those properties are collections again with objects in them - hierarchical data. Maybe some of the properties cant be edited directly because the grid is not smart enough - like SqlTypes.
The Problem
We have a collection of objects that need to go into a windows datagrid. They may or may not have properties that are collections too.
The Solution
We need to create the follwoing objects:
- A class implementing
ITypedListandIBindingList(your collection) - A class that is your data (lots of properties and stuff)
- A class implementing
IComparer(for sorting) - A class implementing
PropertyDescriptor(for using non grig compatable types, like SqlTypes ) - A class implementing
Attribute(so we know whats in the collection)
For those of you that have tryed this and it didnt work, a couple of issues came up that I will discuss.
ITypedList.GetItemProperties(PropertyDescriptor[] listAccessors)
This was the nastiest method interface in the project. The problem has to do with the listAccessors . If the parameter is not null, then the only one that should be processed is the last one. I had to decompile System.Data.DataView.ITypedList.GetItemProperties to find that out. Then I needed to detect our custom collections and return the properties for the underlying data.
SqlPropertyDescriptor : PropertyDescriptor
This one, although straight forward to implement, is a bit tricky in that when calling GetItemProperties and we want to use this PropertyDesciptor instead of the default, we need to replace it in the collection. I wrote this method to do it:
protected PropertyDescriptorCollection GetPropertyDescriptorCollection( ArrayList properties )
{
if ( properties == null || properties.Count == 0 )
return new PropertyDescriptorCollection(null);
ArrayList output = new ArrayList();
foreach ( PropertyDescriptor p in properties )
{
if ( p.Attributes.Matches(new Attribute[]{new BindableAttribute(false)}) ) continue;
if ( p.PropertyType.Namespace == "System.Data.SqlTypes" )
{
// create the base type property descriptor
output.Add(SqlPropertyDescriptor.GetProperty( p.Name, p.PropertyType ) );
}
else
{
output.Add(p);
}
}
return new PropertyDescriptorCollection((PropertyDescriptor[])output.ToArray(typeof(PropertyDescriptor)));
}
After that, it was all straight forward.
The SetValue and GetValue of the PropertyDescriptor provide the means to edit SqlTypes like SqlDateTime . After detecting the namespace of the data type, I use SqlPropertDescriptor which implements GetValue() and SetValue() . These methods try to figure everything out for themselves:
public override void SetValue(object component,object value)
{
try
{
PropertyInfo pi = component.GetType().GetProperty(this.Name);
Object o;
if ( value == DBNull.Value )
{
o = component.GetType().GetField("Null", BindingFlags.Static | BindingFlags.Public | BindingFlags.GetField).GetValue(component);
}
else
{
o = pi.PropertyType.GetConstructor(new Type[]{BaseType}).Invoke(new Object[]{value});
}
pi.SetValue(component,o, null);
}
catch(Exception ex)
{
Debug.WriteLine(ex);
}
}
public override object GetValue(object component)
{
try
{
object Property = component.GetType().GetProperty(this.Name).GetValue(component,null);
// handle nulls
if ( (bool)Property.GetType().GetProperty("IsNull").GetValue(Property,null) ) return DBNull.Value;
object Value = Property.GetType().GetProperty("Value").GetValue(Property,null);
return Value;
}
catch(Exception ex)
{
Debug.WriteLine(ex);
}
return null;
}
Related articles
Related discussion
-
Concurrency violation: the UpdateCommand affected 0 of the expected 1 records
by virtualking (0 replies)
-
How to optimize mysql subquery performance?
by Jayaram P (0 replies)
-
C# video Editing/rendering
by pkuchaliya (0 replies)
-
How to Fill DataSet with more records (around 1 lakh) in a faster way
by Jayaram P (0 replies)
-
Can't print on the network with MSADESS ??
by anatha1 (2 replies)
Related podcasts
-
Object-Oriented Programming in Ruby
In this episode, I talk with Scott Bellware about object-oriented programming in Ruby, and Ruby's object model. This is taken from a private conversation, and the audio quality suffers at times. Much thanks to Scott for allowing this to be released.This episode of the Alt.NET Podcast is bro...
This thread is for discussions of Complex Data Binding.