How can I set the content of a cell in the gridview to be displayed beyond the length by using a ellipsis instead of a line feed? When the mouse moves up, the contents of the Shadow are displayed.

You can use CSS to set ellipsis,
Move the mouse up and show all with tooltip,
1. CSS:
<Style type = "text/CSS">
. Mlength
{
Display: block;
Width: 100px;
Overflow: hidden;
White-space: nowrap;
-O-text-overflow: ellipsis;
Text-overflow: ellipsis;
}
</Style>

2. Set a field in geidview as the template column and set CSS, for example:
<Asp: Label id = "label1" runat = "server" text = '<% # eval ("field") %>'Cssclass = "mlength"> </ASP: Label>

3. Set tooltip in the background:
Protected void gridview1_rowdatabound (Object sender, gridviewroweventargs E)
{
If (E. Row. rowtype = datacontrolrowtype. datarow)
{
(Label) E. row. cells [0]. findcontrol ("label1 ")). tooltip = (Label) E. row. cells [0]. findcontrol ("label1 ")). text;
}
}