业务需求：
业务工作中经常需要对表格中的数据进行处理，包括过滤、复合计算等。过滤需要有过滤条件，复合计算需要计算公式。这两种场景都需要一个表达式编辑器。GridControl自带过滤条件的表达式编辑器，我们要做的就是把这个编辑器拿出来，独立于GridControl，进而可以绑定到其它控件上。
实现原理：
找到表达式编辑器内部类UnboundColumnExpressionEditorForm，这是一个窗口类。我们将其边框设置为None，Dock属性设置为Fill，拖放到控件上，使其看上去像个控件，并公布出获取表达式字符串的方法。
代码片段：
public class UnboundExpressionPanel : PanelControl {
public UnboundExpressionPanel() : base() {
BorderStyle = DevExpress.XtraEditors.Controls.BorderStyles.NoBorder;
StartEdit(new GridColumn());
}
object[] arguments;
protected object[] Arguments { get { return arguments; } }
MyUnboundColumnExpressionEditorForm form = null;
protected MyUnboundColumnExpressionEditorForm Form { get { return form; } }
private GridColumn fUnboundColumn;
public GridColumn UnboundColumn {
get { return fUnboundColumn; }
set {
if (fUnboundColumn == value) return;
StartEdit(value);
}
}
protected MyUnboundColumnExpressionEditorForm CreateForm(params object[] arguments)
{
return new MyUnboundColumnExpressionEditorForm(arguments[0], null);
}
protected void ApplyExpression(string expression) {
if (Arguments == null) return;
((GridColumn)Arguments[0]).UnboundExpression = expression;
}
public void StartEdit(params object[] arguments) {
if (arguments.Length < 1) return;
GridColumn unboundColumn = arguments[0] as GridColumn;
if (unboundColumn == null) return;
fUnboundColumn = unboundColumn;
DestroyForm();
this.arguments = arguments;
this.form = CreateForm(arguments);
if (form == null) return;
form.Dock = DockStyle.Fill;
form.TopLevel = false;
form.FormBorderStyle = FormBorderStyle.None;
form.Closing += new CancelEventHandler(form_Closing);
form.buttonCancel.Click += new EventHandler(buttonCancel_Click);
form.buttonOK.Text = "Apply";
Controls.Add(form);
form.Visible = true;
}
void buttonCancel_Click(object sender, EventArgs e)
{
if (form != null) form.Close();
}
void form_Closing(object sender, CancelEventArgs e)
{
e.Cancel = true;
if (this.arguments == null || this.form == null) return;
if (form.DialogResult == DialogResult.OK)
{
ApplyExpression(form.Expression);
}
else
{
form.ResetMemoText();
}
}
public void DestroyForm()
{
if (form != null) form.Dispose();
form = null;
}
}
public class MyUnboundColumnExpressionEditorForm : UnboundColumnExpressionEditorForm
{
public MyUnboundColumnExpressionEditorForm(object contextInstance,
IDesignerHost designerHost)
: base(contextInstance, designerHost) { }
private string GetExpressionMemoEditText()
{
GridColumn column = ContextInstance as GridColumn;
return null == column ? string.Empty : column.UnboundExpression;
}
public void ResetMemoText()
{
ExpressionMemoEdit.Text = GetExpressionMemoEditText();
}
}
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