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Example E4883
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WinForms Data Grid - Cancel current row modifications at the GridView level

Windows Forms binding allows you to discard changes made in a data item (row/record). This feature is available for data objects that implement IEditableObject (CurrencyManager.CancelCurrentEdit).

Entity Framework 4 comes with POCO support that allows developers to define entities (base classes are not required). By not inheriting from the underlying entities of the framework, developers lost the built-in implementations of IEditableObject and INotifyPropertyChanged interfaces (for example, the capability to undo changes to a grid control if data validation fails).

This example demonstrates how to address this issue at the GridView level. The example creates a custom Grid View. The custom GridView uses a new data controller (inherited from the CurrencyDataController class) and overrides the following methods: BeginCurrentRowEdit, EndCurrentRowEdit, and CancelCurrentRowEdit.

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Example Code

DxSample/Form1.cs(vb) 
C#
using DevExpress.Utils;
using DevExpress.XtraGrid.Views.Base;
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;

namespace DxSample {
    public partial class Form1 :Form {
        public Form1() {
            InitializeComponent();
        }

        private void OnValidateRow(object sender, ValidateRowEventArgs e) {
            Person p = (Person)e.Row;
            e.Valid = string.IsNullOrEmpty(p.Name) || p.Name.Contains("A");
        }
    }
}
DxSample/Grid/CancellingChangesDataController.cs(vb) 
C#
using DevExpress.Data;
using System;
using System.Collections.Generic;
using System.ComponentModel;

namespace DxSample.Grid {
    public class CancellingChangesDataController :CurrencyDataController {
        class ColumnValuePair {
            public DataColumnInfo Column { get; set; }
            public object Value { get; set; }

            public void Free() {
                Column = null;
                Value = null;
            }
        }

        List<ColumnValuePair> originalValues = new List<ColumnValuePair>();

        public bool CanCancelChanges { get; set; }

        bool ShouldCancelChanges {
            get { return CanCancelChanges && CurrentControllerRow != NewItemRow && !(CurrentControllerRowObject is IEditableObject); }
        }

        public override void BeginCurrentRowEdit() {
            base.BeginCurrentRowEdit();
            if (ShouldCancelChanges && originalValues.Count == 0)
                foreach (DataColumnInfo col in Columns)
                    originalValues.Add(new ColumnValuePair() { Column = col, Value = GetCurrentRowValue(col) });
        }

        public override bool EndCurrentRowEdit(bool force) {
            bool result = base.EndCurrentRowEdit(force);
            if (result) {
                foreach (ColumnValuePair val in originalValues)
                    val.Free();
                originalValues.Clear();
            }
            return result;
        }

        public override void CancelCurrentRowEdit() {
            base.CancelCurrentRowEdit();
            foreach (ColumnValuePair val in originalValues) {
                SetCurrentRowValue(val.Column, val.Value);
                val.Free();
            }
            originalValues.Clear();
        }

        public override void Dispose() {
            foreach (ColumnValuePair val in originalValues)
                val.Free();
            originalValues.Clear();
            base.Dispose();
        }
    }
}
DxSample/Grid/GridControlEx.cs(vb) 
C#
using DevExpress.XtraGrid;
using DevExpress.XtraGrid.Registrator;

namespace DxSample.Grid {
    public class GridControlEx :GridControl {
        protected override void RegisterAvailableViewsCore(InfoCollection collection) {
            base.RegisterAvailableViewsCore(collection);
            collection.Add(new GridViewExInfoRegistrator());
        }
    }
}
DxSample/Grid/GridViewEx.cs(vb) 
C#
using DevExpress.Data;
using DevExpress.Utils.Controls;
using DevExpress.Utils.Serializing;
using DevExpress.XtraGrid;
using DevExpress.XtraGrid.Views.Base;
using DevExpress.XtraGrid.Views.Grid;
using System;
using System.ComponentModel;

namespace DxSample.Grid {
    public class GridViewEx :GridView {
        public GridViewEx() : base() { }
        public GridViewEx(GridControl ownerGrid) : base(ownerGrid) { }

        [DesignerSerializationVisibility(DesignerSerializationVisibility.Content), XtraSerializableProperty(XtraSerializationVisibility.Content)]
        public new GridViewExOptionsBehavior OptionsBehavior {
            get { return (GridViewExOptionsBehavior)base.OptionsBehavior; }
        }

        protected override ColumnViewOptionsBehavior CreateOptionsBehavior() {
            return new GridViewExOptionsBehavior(this);
        }

        protected override BaseGridController CreateDataController() {
            if (requireDataControllerType == DataControllerType.Regular)
                return new CancellingChangesDataController();
            return base.CreateDataController();
        }

        protected override string OnCreateLookupDisplayFilter(string text, string displayMember) {
            throw new NotSupportedException("This view cannot be used in lookup editors");
        }

        protected override void UpdateDataControllerOptions() {
            base.UpdateDataControllerOptions();
            CancellingChangesDataController controller = DataController as CancellingChangesDataController;
            if (controller != null)
                controller.CanCancelChanges = OptionsBehavior.CanCancelChanges;
        }
    }
}
DxSample/Grid/GridViewExInfoRegistrator.cs(vb) 
C#
using DevExpress.XtraGrid;
using DevExpress.XtraGrid.Registrator;
using DevExpress.XtraGrid.Views.Base;

namespace DxSample.Grid {
    public class GridViewExInfoRegistrator :GridInfoRegistrator {
        public override string ViewName {
            get { return "GridViewEx"; }
        }

        public override BaseView CreateView(GridControl grid) {
            return new GridViewEx(grid);
        }
    }
}
DxSample/Grid/GridViewExOptionsBehavior.cs(vb) 
C#
using DevExpress.Utils.Controls;
using DevExpress.XtraGrid.Views.Base;
using DevExpress.XtraGrid.Views.Grid;
using System.ComponentModel;

namespace DxSample.Grid {
    public class GridViewExOptionsBehavior :GridOptionsBehavior {
        public GridViewExOptionsBehavior() : base() { }
        public GridViewExOptionsBehavior(ColumnView view) : base(view) { }

        bool fCanCancelChanges;
        [DefaultValue(false)]
        public bool CanCancelChanges {
            get { return fCanCancelChanges; }
            set {
                if (fCanCancelChanges == value) return;
                bool prevValue = CanCancelChanges;
                fCanCancelChanges = value;
                OnChanged(new BaseOptionChangedEventArgs("CanCancelChanges", prevValue, CanCancelChanges));
            }
        }

        public override void Assign(BaseOptions options) {
            BeginUpdate();
            try {
                base.Assign(options);
                GridViewExOptionsBehavior opt = options as GridViewExOptionsBehavior;
                if (opt == null) return;
                fCanCancelChanges = opt.CanCancelChanges;
            } finally { EndUpdate(); }
        }
    }
}
DxSample/Person.cs(vb) 
C#
using System.ComponentModel;

namespace DxSample {
    public class Person {
        public string Name { get; set; }
    }
}

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