GridView with Multiple Rows Selected, Controls in the Template Column and Edit Mode

It is common to implement selection of multiple rows in a  GridView with a help of checkbox control embedded in the TemplateColumn.  You will have to write something like this in your ASPX.

        <asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="False" 
                        DataSourceID="SqlDataSource" >
            <Columns>
                <asp:TemplateField>
                    <ItemTemplate>
                        <asp:CheckBox ID="CheckBox1" runat="server" />
                    </ItemTemplate>
                </asp:TemplateField>
                <asp:BoundField DataField="Name" HeaderText="Name" />
                <asp:BoundField DataField="ModifiedDate" HeaderText="ModifiedDate" />
                <asp:CommandField ShowEditButton="True" />
            </Columns>
        </asp:GridView>

However, if you also need to to support data editing in the GridView and you add CommandField column with ShowEditButton="True" you will find that your solution does not work as desired. 

If you click on "edit" link when you have several rows selected in your GridView, you lose your selection.  This behavior does not depend on EnableViewState value.

This strange behavior is explained by the following:

CheckBox control restores its Checked property from the post-data submitted by the browser on post-back.  Post-data processing triggers data binding of the GridView control and post-data are processed before the OnLoad phase in the page lifecycle.  However, when GridView handles Click event on [Edit] LinkButton in the command column, GridView needs to redo data binding again to create edit row.  This second data binding in the page lifecycle create new CheckBox controls which never process post-data and their Checked property value remains false.  It can be easily seen if you enable page Trace and handle DataBinding event in the GridView by the following handler:

    protected void GridView1_DataBinding(object sender, EventArgs e) {
        Trace.Write("DATABINDING");
    }

Now, when you click on [Edit] link in any row, your trace will be similar to: 

Note two DATABINDING twice in the trace log.

Solution

The simplest solution that works for me is to store references to selected rows in the ViewState and restore state of checkboxes on data binding.  This can easily accomplished by:

    protected void CheckBox1_CheckedChanged(object sender, EventArgs e) {
        CheckBox checkbox = (CheckBox)sender;
        if (checkbox.Checked) {
            ViewState[checkbox.UniqueID] = true;
        }
        else {
            ViewState.Remove(checkbox.UniqueID);
        }
    }

    protected void CheckBox1_DataBinding(object sender, EventArgs e) {
        CheckBox checkbox = (CheckBox)sender;
        checkbox.Checked = ViewState[checkbox.UniqueID] != null;
    }

CheckBox must be configured as:

    <asp:CheckBox ID="CheckBox1" runat="server" 
    OnCheckedChanged="CheckBox1_CheckedChanged" OnDataBinding="CheckBox1_DataBinding"/>

It requires page ViewState to be enabled, of course.

UPDATE:

Sure this solution will not work with inserts or deletes being made to data source, unless you replace checkbox.UniqueID with the value of key field in the data source.