Generic State Collection

Introduction

While building custom ASP.NET controls I often need to implement IStateManager for collections of objects in order to persist them in ViewState.
The common way was to create collection by inherit List<T> and implementing IStateManager.
In most of the cases the code was same, I just have to change the generic type of the list.
That's why it was a perfect candidate for generic implementation. Implementation which made

The Generic State Collection gave me the ability to use any kind of state collections without a line of additional code.

The Code

StateCollection inherits List<T> class and implements IStateManager. Please, note I'm requiring the generic type of StateCollection to be one that implements IStateManager by itself.

Here is the source code of StateCollection class:

/// <summary>
/// 
/// </summary>
/// <typeparam name="T"></typeparam>
public class StateCollection<T> : List<T>, IStateManager where T : IStateManager, new(){

#region Fields  /////////////////////////////////////////////////////////////////

bool _tracking;

#endregion

#region Properties  /////////////////////////////////////////////////////////////

/// <summary>
/// When implemented by a class, gets a value indicating whether a server control is tracking its view state changes.
/// </summary>
/// <value></value>
/// <returns>true if a server control is tracking its view state changes; otherwise, false.</returns>
public bool IsTrackingViewState {
    get { return _tracking; }
}
#endregion

#region Methods /////////////////////////////////////////////////////////////////

/// <summary>
/// Loads the state of the view.
/// </summary>
/// <param name="savedState">State of the saved.</param>
public void LoadViewState(object savedState) {

    object[] state = savedState as object[];
    if (state != null) {
        T item;
        bool exists;
        for (int i = 0; i < state.Length; i++) {
            item = (exists =( i < this.Count)) ? this[i] : new T();
            item.LoadViewState(state[i]);
            if (this.IsTrackingViewState)
                item.TrackViewState();
            if(!exists) Add(item);
        }
    }
}

/// <summary>
/// When implemented by a class, saves the changes to a server control's view state to an <see cref="T:System.Object"/>.
/// </summary>
/// <returns>
/// The <see cref="T:System.Object"/> that contains the view state changes.
/// </returns>
public object SaveViewState() {

    if (this.Count > 0) {
        int count = this.Count;
        object[] state = new object[count];
        for (int i = 0; i < count; i++) {
            state[i] = this[i].SaveViewState();
        }
        return state;
    }
    else
        return null;
}

/// <summary>
/// When implemented by a class, instructs the server control to track changes to its view state.
/// </summary>
public void TrackViewState() {
    _tracking = true;
}
#endregion
}

Points of Interest

As example of how to use StateCollection you can refer to GoogleMap Control source code.

History

• 22.Mar.2008 - Initial release