This example shows how to customize the Expression Editor as follows:
- Remove the Now function from the list of Date-Time functions and prevent users from using this function in expressions (display an error message).
- Disable capitalization of function names.
- Implement a color provider to use a custom palette for syntax highlighting.
- Rename the Columns category to Fields.
- Implement a custom Expression Editor view to display only specific UI elements of the Expression Editor.
Right-click the Expression column header and select the Expression Editor… command in the context menu to invoke the Expression Editor.
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Example Code
C#using DevExpress.Data.Controls.ExpressionEditor;
using DevExpress.Data.Filtering;
using DevExpress.Data.Filtering.Helpers;
using DevExpress.DataAccess.ExpressionEditor;
using DevExpress.DataAccess.UI.ExpressionEditor;
using DevExpress.DataAccess.UI.Native.ExpressionEditor;
using DevExpress.LookAndFeel;
using DevExpress.XtraEditors;
using System;
using System.Collections.Generic;
using System.Drawing;
using System.Linq;
namespace WindowsFormsApplication1 {
public partial class Form1 : XtraForm {
public class Product {
public Product(int productID, string productName, Category category) {
ProductID = productID;
ProductName = productName;
Category = category;
}
public int ProductID { get; }
public string ProductName { get; }
public int? SupplierID { get; set; }
public int? CategoryID { get; set; }
public short? UnitsOnOrder { get; set; }
public bool Discontinued { get; set; }
public Category Category { get; }
}
public class Category {
public int CategoryID { get; set; }
public string CategoryName { get; set; }
}
static List<Product> GetProductsList() {
var categoryBeverages = new Category { CategoryID = 1, CategoryName = "Beverages" };
var categoryConfections = new Category { CategoryID = 2, CategoryName = "Condiments" };
return new List<Product> {
new Product(1, "Chai", categoryBeverages),
new Product(2, "Chang", categoryBeverages),
new Product(3, "Coffee", categoryBeverages),
new Product(4, "Chocolade", categoryConfections),
new Product(5, "Maxilaku", categoryConfections),
new Product(6, "Valkoinen suklaa", categoryConfections),
};
}
public Form1() {
InitializeComponent();
this.gridControl1.DataSource = GetProductsList();
}
void gridView1_UnboundExpressionEditorCreated(object sender, DevExpress.XtraGrid.Views.Base.UnboundExpressionEditorEventArgs e) {
if(e.ExpressionEditorContext == null) {
return;
}
// Exclude "Now" from the list of available functions.
var nowFunction = e.ExpressionEditorContext.Functions.FirstOrDefault(fi => string.Equals(fi.Name, "now", StringComparison.OrdinalIgnoreCase));
if(nowFunction != null) {
e.ExpressionEditorContext.Functions.Remove(nowFunction);
}
// Uncomment the following line to use a custom color provider.
//e.ExpressionEditorContext.ColorProvider = new CustomColorProvider();
// Implement a custom criteria validator (e.g., to forbid using a specific function).
e.ExpressionEditorContext.CriteriaOperatorValidatorProvider = new ValidatorProvider();
// Disable capitalization of function names in expressions.
e.ExpressionEditorContext.OptionsBehavior.CapitalizeFunctionNames = false;
// Rename the "Columns" category to "Fields".
foreach(var columnInfo in e.ExpressionEditorContext.Columns) {
columnInfo.Category = "Fields";
}
// Uncomment the following line to use a custom Expression Editor view.
//e.ExpressionEditorView = new CustomExpressionEditorView(this.LookAndFeel, new CustomExpressionEditorControl());
}
}
class ValidatorProvider : ICriteriaOperatorValidatorProvider {
#region Implementation of ICriteriaOperatorValidatorProvider
public ErrorsEvaluatorCriteriaValidator GetCriteriaOperatorValidator(ExpressionEditorContext context) {
return new Validator(context);
}
#endregion
}
class Validator : CriteriaOperatorValidator {
public Validator(ExpressionEditorContext context)
: base(context, supportsAggregates: true) {
}
#region Overrides of CriteriaOperatorValidator
public override void Visit(FunctionOperator theOperator) {
if (theOperator.OperatorType == FunctionOperatorType.Now) {
this.errors.Add(new CriteriaValidatorError("Invalid function: now()"));
}
base.Visit(theOperator);
}
#endregion
}
class CustomColorProvider : IExpressionEditorColorProvider {
public Color GetColorForElement(ExpressionElementKind elementKind) {
if (elementKind == ExpressionElementKind.Column)
return Color.BlueViolet;
if (elementKind == ExpressionElementKind.Function)
return Color.Brown;
return Color.Azure;
}
}
public class CustomExpressionEditorView : ExpressionEditorView {
public CustomExpressionEditorView(UserLookAndFeel lookAndFeel, ExpressionEditorControl expressionEditor)
: base(lookAndFeel, expressionEditor) {
}
}
public class CustomExpressionEditorControl : ExpressionEditorControl {
#region Overrides of ExpressionEditorControl
protected override ExpressionDocumentationControl CreateDocumentationControl() {
return null;
}
#endregion
}
}