[Silverlight]实现DataGrid使用CheckBox选择行

在DataGrid中使用CheckBox选择行时典型的错误就是CheckBox没有Binding到任何属性上，这样的话当拖动滚动条时CheckBox.IsChecked就会乱掉，如Demo中左边那个DataGrid所示。最直观的解决方法是禁用DataGrid的滚动条，或者在绑定的数据上添加一个用于绑定CheckBox的bool属性。
其实只要在DataGrid.LoadingRow事件中将CheckBox的DataContext设定为另外一个Object，就不需要牺牲DataGrid的高效能，也不需要改变原有数据的结构。具体实现如下：

MainPage.xaml  <my:MyDataGrid ItemsSource="{Binding}"
                       AutoGenerateColumns="False">
            <my:MyDataGrid.Columns>
                <sdk:DataGridTextColumn Header="Name"
                                        Binding="{Binding Name}"
                                        Width="*" />
                <sdk:DataGridTextColumn Header="GUID"
                                        Binding="{Binding GUID}"
                                        Width="*" />
            </my:MyDataGrid.Columns>
        </my:MyDataGrid>

MyDataGrid.cs public class MyDataGrid : DataGrid
    {
        private const string HeaderCheckBoxName = "select_column_checkbox";

        private Dictionary<object, MarkObject> _markObjects;
        private DataGridTemplateColumn _selectColumn;
        private CheckBox _selectCheckBox;

        public MyDataGrid()
        {
            _markObjects = new Dictionary<object, MarkObject>();

            _selectColumn = new DataGridTemplateColumn();
            _selectColumn.HeaderStyle = GetHeaderStyle();
            _selectColumn.CellTemplate = GetCellTemplate();
            this.Columns.Insert(0, _selectColumn);
            this.SizeChanged += new SizeChangedEventHandler(OnSizeChanged);
        }

        public void SelectAll()
        {
            if (_selectCheckBox != null)
                _selectCheckBox.IsChecked = true;
            SetAllSelectedStates(true);
        }

        public void UnselectAll()
        {
            if (_selectCheckBox != null)
                _selectCheckBox.IsChecked = false;
            SetAllSelectedStates(false);
        }

        public List<T> GetSelectedItems<T>()
        {
            List<T> result = new List<T>();
            if (ItemsSource != null)
            {
                var enu = ItemsSource.GetEnumerator();
                while (enu.MoveNext())
                {
                    if (GetMarkObject(enu.Current).Selected)
                        result.Add((T)enu.Current);
                }
            }
            return result;
        }

        protected override void OnLoadingRow(DataGridRowEventArgs e)
        {
            base.OnLoadingRow(e);

            object dataContext = e.Row.DataContext;
            FrameworkElement element = _selectColumn.GetCellContent(e.Row);
            element.DataContext = GetMarkObject(dataContext);
        }

        private Style GetHeaderStyle()
        {
            Style style = new System.Windows.Style();
            style.TargetType = typeof(ContentControl);

            StringBuilder tmp = new StringBuilder();
            tmp.Append("<DataTemplate ");
            tmp.Append("xmlns='http://schemas.microsoft.com/winfx/2006/xaml/presentation' ");
            tmp.Append("xmlns:x='http://schemas.microsoft.com/winfx/2006/xaml' >");
            tmp.Append(string.Format("<CheckBox  Content='Select All' x:Name='{0}' VerticalAlignment='Center' HorizontalAlignment='Center' />", HeaderCheckBoxName));
            tmp.Append("</DataTemplate>");
            DataTemplate contentTemplate = XamlReader.Load(tmp.ToString()) as DataTemplate;

            style.Setters.Add(new Setter(ContentControl.ContentTemplateProperty, contentTemplate));
            return style;
        }

        private DataTemplate GetCellTemplate()
        {
            StringBuilder tmp = new StringBuilder();
            tmp.Append("<DataTemplate ");
            tmp.Append("xmlns='http://schemas.microsoft.com/winfx/2006/xaml/presentation' ");
            tmp.Append("xmlns:x='http://schemas.microsoft.com/winfx/2006/xaml' >");
            tmp.Append("<CheckBox IsChecked='{Binding Selected,Mode=TwoWay}' VerticalAlignment='Center' HorizontalAlignment='Center' />");
            tmp.Append("</DataTemplate>");
            return XamlReader.Load(tmp.ToString()) as DataTemplate;
        }

        private MarkObject GetMarkObject(Object obj)
        {
            if (_markObjects.ContainsKey(obj) == false)
            {
                MarkObject markObject;
                markObject = new MarkObject();
                _markObjects.Add(obj, markObject);
            }

            return _markObjects[obj];
        }

        private void OnSizeChanged(object sender, SizeChangedEventArgs e)
        {
            _selectCheckBox = this.GetChild<CheckBox>(HeaderCheckBoxName);
            if (_selectCheckBox == null)
                return;

            _selectCheckBox.Checked += (sender2, e2) => SetAllSelectedStates(true);
            _selectCheckBox.Unchecked += (sender2, e2) => SetAllSelectedStates(false);
        }

        private void SetAllSelectedStates(bool value)
        {
            if (ItemsSource == null)
                return;

            var enu = ItemsSource.GetEnumerator();
            while (enu.MoveNext())
            {
                GetMarkObject(enu.Current).Selected = value;
            }
        }




    }

其中MarkObject是一个继承INotifyPropertyChanged的类,包含Selected属性，这样更改Selected时可以更新UI。在构造函数中直接插入了个模板列，模板列使用XamlReader.Load(string str)方法直接在代码中创建模板。至于列头的CheckBox则在SizeChanged事件时才可以通过VisualTreeHelper.GetChild递归找到。

欢迎指正。