Viewstate, datatable and properties!

Question

Hello,

Im developing a user control that contains two RadGrids. When a user selects a row in grid 1, the page postsback. At that point, I create a Datatable and DataRow and add it to grid 2's datasource.

The problem I am experiencing overall is that the datatable is lost and re-created every time the page is posted back. I therefore tried to save the datatable in the viewstate using a property, but that doesnt seem to have helped. I'm pretty new to using properties full stop, so my code is perhaps wrong.

My solution:

    public class DynamicDocumentSelectorWebUITypeEditor : Telerik.Cms.Web.UI.WebUITypeEditor<string>
    {

    private System.Data.DataTable _oDataTable;

public System.Data.DataTable getTable() {

        System.Data.DataTable oDataTable = new System.Data.DataTable();
        oDataTable.Columns.Add(new System.Data.DataColumn("DocumentID", typeof(string)));
        oDataTable.Columns.Add(new System.Data.DataColumn("DocumentName", typeof(string)));
        oDataTable.Columns.Add(new System.Data.DataColumn("DocumentExtension", typeof(string)));

        return oDataTable;

    }

public System.Data.DataTable oDataTable {
        get {
            object o = this.ViewState["DataTable"];
            if(o == null) {
                return _oDataTable;
            }
            return (System.Data.DataTable)o;
        }
        set {
            this._oDataTable = value;
            this.ViewState["DataTable"] = value;
        }
    }

    protected override void CreateChildControls() {
        base.CreateChildControls();

        if (this.oDataTable == null) {

            this.oDataTable = getTable();

        }

        }

//the following function is executed when a row in grid 1 is selected
    protected void GridDocumentsInLibrary_SelectedIndexChanged(object sender, EventArgs e) {

        //loop through each selected row
        foreach (Telerik.Web.UI.GridDataItem oItem in GridDocumentsInLibrary.SelectedItems) {

            //System.Data.DataTable oDt = this.oDataTable;

            foreach (System.Data.DataRow oDataRow in this.oDataTable.Rows) {

                //check whether the row already exists in the datatable
                //if (oDataRow["DocumentID"] != oItem["DocumentID"].Text) {

                    System.Data.DataRow dr = this.oDataTable.NewRow();
                    dr["DocumentID"] = oItem["DocumentID"].Text;
                    dr["DocumentName"] = oItem["DocumentName"].Text;
                    dr["DocumentExtension"] = oItem["DocumentExtension"].Text;
                    this.oDataTable.Rows.Add(dr);

                //}

            }

        }

        //set datasource of second grid
        GridSelectedDocuments.DataSource = this.oDataTable;
        GridSelectedDocuments.DataBind();

    }

}

Am i doing this completely wrong? Can anyone help?

Thanks in advance higgsy

Answer 1

Are you calling Page.DataBind without checking whether or not Page.IsPostBack is true? This would cause the second grid to rebind and, without a defined datasource, will be empty.

Other than that, defining the datasource and binding it in SelectedIndexChanged, if ViewState is enabled, the second RadGrid should persist it's data.