Custom Categories and Functions

As of R1 2019, the RadExpressionEditor control allows users to add custom categories and functions to its UI as well as remove some of the already defined ones.

To do so, you have to create a custom implementation of the ExpressionEditorViewModel and override its virtual methods.

Example 1: The ExpressionEditorViewModel overrides

public class CustomExpressionEditorViewModel : ExpressionEditorViewModel 
{ 
    protected override IEnumerable<EditorCategoryModel> GenerateCategories() 
    { 
        return base.GenerateCategories(); 
    } 
 
    protected override IEnumerable<EditorModelBase> GetFunctionsItemModels() 
    { 
        return base.GetFunctionsItemModels(); 
    } 
 
    protected override IEnumerable<EditorModelBase> GetFieldsItemModels(object currentItem) 
    { 
        return base.GetFieldsItemModels(currentItem); 
    } 
 
    protected override IEnumerable<EditorModelBase> GetOperatorsItemModels() 
    { 
        return base.GetOperatorsItemModels(); 
    } 
 
    protected override IEnumerable<EditorModelBase> GetConstantsItemModels() 
    { 
        return base.GetConstantsItemModels(); 
    } 
 
    protected override EditorCategoryModel GetFieldsCategory() 
    { 
        return base.GetFieldsCategory(); 
    } 
} 

To assign the custom viewmodel to the RadExpressionEditor control, you have to set its ViewModel property.

Example 2: Set RadExpressionEditor's ViewModel

this.ExpressionEditor.ViewModel = new CustomExpressionEditorViewModel(); 

Custom Categories

To add custom categories as well as remove certain predefined categories, you need to override the GenerateCategories method.

Example 3: Add custom categories

protected override IEnumerable<EditorCategoryModel> GenerateCategories() 
{ 
    List<EditorCategoryModel> list = new List<EditorCategoryModel>(base.GenerateCategories()); 
 
    EditorCategoryModel favorites = new EditorCategoryModel("Favorites"); 
    EditorCategoryModel math = new EditorCategoryModel("Math"); 
    EditorCategoryModel dateTime = new EditorCategoryModel("DateTime"); 
 
    math.Children.Add(new FunctionEditorItemModel(typeof(Math).GetMethod("Abs", BindingFlags.Public | BindingFlags.Static, null, new Type[] { typeof(double) }, null), favorites.Name)); 
    math.Children.Add(new FunctionEditorItemModel(typeof(Math).GetMethod("Acos", BindingFlags.Public | BindingFlags.Static), favorites.Name)); 
    math.Children.Add(new FunctionEditorItemModel(typeof(Math).GetMethod("Atan", BindingFlags.Public | BindingFlags.Static), favorites.Name)); 
    math.Children.Add(new FunctionEditorItemModel(typeof(Math).GetMethod("Sqrt", BindingFlags.Public | BindingFlags.Static), favorites.Name)); 
    dateTime.Children.Add(new FunctionEditorItemModel(typeof(DateTime).GetMethod("IsLeapYear", BindingFlags.Public | BindingFlags.Static), favorites.Name)); 
 
    favorites.Children.Add(math); 
    favorites.Children.Add(dateTime); 
 
    list.Add(favorites); 
 
    return list; 
} 

Example 3 adds a Favorites category with two subcategories - Math and DateTime. Each of the categories contains some static methods of the respective class. The results before and after respectively can be observed in Figure 1.

Figure 1: Custom category

Custom Functions

If you want to add your custom non-static functions to the control you need to set the ExpressionFunctionContext.Context property to an instance of the ExpressionFunctionContext class.

Example 4: Custom ExpressionFunctionContext

public class CustomExpressionFunctionContext : ExpressionFunctionContext 
{ 
    [Description("Increase the value by 1")] 
    public int OnePlus(int input) 
    { 
        return ++input; 
    } 
 
    [Description("Increase the value with 2")] 
    public int TwoPlus(int input) 
    { 
        return input + 2; 
    } 
} 

Example 4 defines two custom instance functions which we can now pass to the ExpressionParser as show in Example 5.

Example 5: Set the ExpressionFunctionContext.Context

ExpressionFunctionContext.Context = new CustomExpressionFunctionContext(); 

You can then add these functions in the GetFunctionsItemModels override as well as remove some of the predefined functions.

Example 6: Add custom functions

protected override IEnumerable<EditorModelBase> GetFunctionsItemModels() 
{ 
    List<EditorModelBase> list = new List<EditorModelBase>(base.GetFunctionsItemModels()); 
 
    var other = list.First(x => x.Name == "Other") as EditorCategoryModel; 
    other.Children.Insert(5, new FunctionEditorItemModel(typeof(CustomExpressionFunctionContext).GetMethod("OnePlus", BindingFlags.Public | BindingFlags.Instance), other.Name)); 
    other.Children.Add(new FunctionEditorItemModel(typeof(CustomExpressionFunctionContext).GetMethod("TwoPlus", BindingFlags.Public | BindingFlags.Instance), other.Name)); 
 
    return list; 
} 

Example 6 adds the two custom functions defined in Example 4 to the Other subcategory. The results before and after respectively are illustrated in Figure 2.

Figure 2: Custom functions

Further Customizations

You can further customize the control by overriding the GetFieldsItemModels, GetOperatorsItemModels, GetConstantsItemModels and GetFieldsCategory methods.

Example 7: Remove operators, constants and fields and add subcategories to the Fields category

protected override IEnumerable<EditorModelBase> GetOperatorsItemModels() 
{ 
    List<EditorModelBase> list = new List<EditorModelBase>(base.GetOperatorsItemModels()); 
 
    list.RemoveAll(m => m.Name.StartsWith("/", System.StringComparison.CurrentCultureIgnoreCase)); 
    list.RemoveAll(m => m.Name.StartsWith("Or", System.StringComparison.CurrentCultureIgnoreCase)); 
    list.RemoveAll(m => m.Name.StartsWith("And", System.StringComparison.CurrentCultureIgnoreCase)); 
    list.RemoveAll(m => m.Name.StartsWith("Not", System.StringComparison.CurrentCultureIgnoreCase)); 
 
    return list; 
} 
 
protected override IEnumerable<EditorModelBase> GetConstantsItemModels() 
{ 
    List<EditorModelBase> list = new List<EditorModelBase>(base.GetConstantsItemModels()); 
 
    list.RemoveAll(m => m.Name.StartsWith("null", System.StringComparison.CurrentCultureIgnoreCase)); 
 
    return list; 
} 
 
protected override IEnumerable<EditorModelBase> GetFieldsItemModels(object currentItem) 
{ 
    List<EditorModelBase> list = new List<EditorModelBase>(base.GetFieldsItemModels(currentItem)); 
 
    list.RemoveAll(m => m.Name.StartsWith("Discontinued", System.StringComparison.CurrentCultureIgnoreCase)); 
 
    return list; 
} 
 
protected override EditorCategoryModel GetFieldsCategory() 
{ 
    var fields = base.GetFieldsCategory(); 
    if (fields.Children.Any()) 
    { 
        var subcategory = new EditorCategoryModel("Subcategory"); 
        subcategory.Children.Add(fields.Children.First(x => x.Name == "Car")); 
        fields.Children.Add(subcategory); 
    } 
 
    return fields; 
} 

The example above removes some of the operators, constants and the Discontinued field from the RadExpressionEditor. It also creates a subcategory for the Fields category which holds the Car field of the bound object.

See Also

• Lambdas