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CustomRule

A rule with custom validation logic.

Type:

Object

To specify the custom rule, set the type to "custom" and declare the validationCallback function.

You can also set a custom message, specify whether empty values are valid, and whether the rule should be re-evaluated, even if the target value is the same.

See Also

ignoreEmptyValue

If true, the validationCallback is not executed for null, undefined, false, and empty strings.

Type:

Boolean

Default Value: false

message

Specifies the message that is shown if the rule is broken.

Type:

String

Default Value: 'Value is invalid'

An error message can be specified as follows:

  • Hard-code the message

    jQuery
    index.js
    $(function() {
        $("#textBox").dxTextBox({ ... })
            .dxValidator({
                type: "custom",
                message: "My custom message"
            });
    });
    Angular
    app.component.html
    app.module.ts
    <dx-text-box> 
        <dx-validator>
            <dxi-validation-rule 
                type="custom" 
                message="My custom message">
            </dxi-validation-rule>
        </dx-validator>
    </dx-text-box>
    import { BrowserModule } from '@angular/platform-browser';
    import { NgModule } from '@angular/core';
    import { AppComponent } from './app.component';
    
    import { DxValidatorModule,
             DxTextBoxModule } from 'devextreme-angular';
    
    @NgModule({
        declarations: [
            AppComponent
        ],
        imports: [
            DxTextBoxModule,
            BrowserModule,
            DxValidatorModule
        ],
        providers: [],
        bootstrap: [AppComponent]
    })
    export class AppModule { }
    Vue
    App.vue
    <template>
        <DxTextBox>
            <DxValidator>
                <DxCustomRule
                    message="My custom message"
                />
            </DxValidator>
        </DxTextBox>
    </template>
    
    <script>
    import 'devextreme/dist/css/dx.common.css';
    import 'devextreme/dist/css/dx.light.css';
    
    import { DxTextBox } from 'devextreme-vue/text-box';
    import {
        DxValidator,
        DxCustomRule
    } from 'devextreme-vue/validator';
    
    export default {
        components: {
            DxTextBox,
            DxValidator,
            DxCustomRule
        }
    }
    </script>
    React
    App.js
    import React from 'react';
    
    import 'devextreme/dist/css/dx.common.css';
    import 'devextreme/dist/css/dx.light.css';
    
    import { TextBox } from 'devextreme-react/text-box';
    import {
        Validator,
        CustomRule
    } from 'devextreme-react/validator';
    
    class App extends React.Component {
        render() {
            return (
                <TextBox>
                    <Validator>
                        <CustomRule
                            message="My custom message" />
                    </Validator>
                </TextBox>
            );
        }
    }
    export default App;
  • Hide the message

    jQuery
    index.js
    $(function() {
        $("#textBox").dxTextBox({ ... })
            .dxValidator({
                type: "custom",
                message: ""
            });
    });
    Angular
    app.component.html
    app.module.ts
    <dx-text-box>
        <dx-validator>
            <dxi-validation-rule 
                type="custom" 
                message="">
            </dxi-validation-rule>
        </dx-validator>
    </dx-text-box>
    import { BrowserModule } from '@angular/platform-browser';
    import { NgModule } from '@angular/core';
    import { AppComponent } from './app.component';
    
     import { DxValidatorModule,
              DxTextBoxModule } from 'devextreme-angular';
    
    @NgModule({
        declarations: [
            AppComponent
        ],
        imports: [
            BrowserModule,
            DxValidatorModule,
            DxTextBoxModule
        ],
        providers: [],
        bootstrap: [AppComponent]
    })
    export class AppModule { }
    Vue
    App.vue
    <template>
        <DxTextBox>
            <DxValidator>
                <DxCustomRule
                    message=""
                />
            </DxValidator>
        </DxTextBox>
    </template>
    
    <script>
    import 'devextreme/dist/css/dx.common.css';
    import 'devextreme/dist/css/dx.light.css';
    
    import { DxTextBox } from 'devextreme-vue/text-box';
    import {
        DxValidator,
        DxCustomRule
    } from 'devextreme-vue/validator';
    
    export default {
        components: {
            DxTextBox,
            DxValidator,
            DxCustomRule
        }
    }
    </script>
    React
    App.js
    import React from 'react';
    
    import 'devextreme/dist/css/dx.common.css';
    import 'devextreme/dist/css/dx.light.css';
    
    import { TextBox } from 'devextreme-react/text-box';
    import {
        Validator,
        CustomRule
    } from 'devextreme-react/validator';
    
    class App extends React.Component {
        render() {
            return (
                <TextBox>
                    <Validator>
                        <CustomRule
                            message="" />
                    </Validator>
                </TextBox>
            );
        }
    }
    export default App;
  • Display the editor's name in the message

    jQuery
    index.js
    $(function() {
        $("#textBox").dxTextBox({ ... })
            .dxValidator({
                name: "Password", // The error message will be "Password is invalid"
                validationRules: [{
                    type: "custom"
                }]
            });
    });
    Angular
    app.component.html
    app.module.ts
    <dx-text-box>
        <!-- The error message will be "Password is invalid" -->
        <dx-validator name="Password">
            <dxi-validation-rule 
                type="custom">
            </dxi-validation-rule>
        </dx-validator>
    </dx-text-box>
    import { BrowserModule } from '@angular/platform-browser';
    import { NgModule } from '@angular/core';
    import { AppComponent } from './app.component';
    
    import { DxValidatorModule,
             DxTextBoxModule } from 'devextreme-angular';
    
    @NgModule({
        declarations: [
            AppComponent
        ],
        imports: [
            BrowserModule,
            DxValidatorModule,
            DxTextBoxModule
        ],
        providers: [],
        bootstrap: [AppComponent]
    })
    export class AppModule { }
    Vue
    App.vue
    <template>
        <DxTextBox>
            <!-- The error message will be "Password is invalid" -->
            <DxValidator name="Password">
                <DxCustomRule />
            </DxValidator>
        </DxTextBox>
    </template>
    
    <script>
    import 'devextreme/dist/css/dx.common.css';
    import 'devextreme/dist/css/dx.light.css';
    
    import { DxTextBox } from 'devextreme-vue/text-box';
    import {
        DxValidator,
        DxCustomRule
    } from 'devextreme-vue/validator';
    
    export default {
        components: {
            DxValidator,
            DxCustomRule
        }
    }
    </script>
    React
    App.js
    import React from 'react';
    
    import 'devextreme/dist/css/dx.common.css';
    import 'devextreme/dist/css/dx.light.css';
    
    import { TextBox } from 'devextreme-react/text-box';
    import {
        Validator,
        CustomRule
    } from 'devextreme-react/validator';
    
    class App extends React.Component {
        render() {
            return (
                <TextBox>
                    {/* The error message will be "Password is invalid" */}
                    <Validator name="Password">
                        <CustomRule} />
                    </Validator>
                </TextBox>
            );
        }
    }
    
    export default App;

reevaluate

Indicates whether the rule should be always checked for the target value or only when the target value changes.

Type:

Boolean

Default Value: false

type

Specifies the rule type. Set it to "custom" to use the CustomRule.

Type:

String

Accepted Values: 'required' | 'numeric' | 'range' | 'stringLength' | 'custom' | 'compare' | 'pattern' | 'email' | 'async'

validationCallback

A function that validates the target value.

Type:

Function

Function parameters:
options:

Object

An object defining validation parameters.

Object structure:
Name Type Description
column

Object

The column to which the cell being validated belongs. Exists only when you validate a built-in editor in the DataGrid or TreeList.

data

Object

The current row's data. Exists only when you validate a DataGrid or TreeList cell's value.

formItem

Object

The form item being validated. Exists only when you validate a built-in editor in the Form UI component.

rule

Object

The rule being checked.

validator

Object

The Validator object that initiated the validation.

value

String

|

Number

The validated value.

Return Value:

Boolean

true if the value is valid; otherwise, false.

The following code shows a validationCallback example. The function accepts a number and returns true if the number is even and false if it is odd:

jQuery
JavaScript
$(function () {
    $("#numberBoxContainer").dxNumberBox({
        value: 4
    }).dxValidator({
        validationRules: [{
            type: "custom",
            validationCallback: validateNumber,
            message: "An even number is expected"
        }]
    });
});
function validateNumber (e) {
    return e.value % 2 == 0;
}
Angular
HTML
TypeScript
<dx-number-box [value]="4">
    <dx-validator>
        <dxi-validation-rule type="custom" 
            [validationCallback]="validateNumber" 
            message="An even number is expected">
        </dxi-validation-rule>
    </dx-validator>
</dx-number-box>
import { DxNumberBoxModule, DxValidatorModule } from "devextreme-angular";
// ...
export class AppComponent {
    validateNumber(e) {
        return e.value % 2 == 0;
    }
}
@NgModule({
    imports: [
        DxNumberBoxModule,
        DxValidatorModule,
        // ...
    ],
    // ...
})
Vue
App.vue
<template>
    <DxNumberBox :value="4">
        <DxValidator>
            <DxCustomRule
                :validation-callback="validateNumber"
                message="An even number is expected"
            />
        </DxValidator>
    </DxNumberBox>
</template>

<script>
import 'devextreme/dist/css/dx.common.css';
import 'devextreme/dist/css/dx.light.css';

import DxNumberBox from 'devextreme-vue/number-box';
import DxValidator, {
    DxCustomRule
} from 'devextreme-vue/validator';

export default {
    components: {
        DxNumberBox,
        DxValidator,
        DxCustomRule
    },
    methods: {
        validateNumber(e) {
            return e.value % 2 == 0;
        }
    }
}
</script>
React
App.js
import React from 'react';

import 'devextreme/dist/css/dx.common.css';
import 'devextreme/dist/css/dx.light.css';

import NumberBox from 'devextreme-react/number-box';
import Validator, {
    CustomRule
} from 'devextreme-react/validator';

class App extends React.Component {
    validateNumber(e) {
        return e.value % 2 == 0;
    }

    render() {
        return (
            <NumberBox defaultValue={4}>
                <Validator>
                    <CustomRule
                        validationCallback={this.validateNumber}
                        message="An even number is expected"
                    />
                </Validator>
            </NumberBox>
        );
    }
}
export default App;