How to create a VForm component with validation functionality like Vuetify in Vue 2?

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In Vuetify, you can set up code like below and the VForm component can automatically check if all inputs within VForm are valid without passing any props back and forth. How can I achieve this functionality for my own form and input components in Vue 2?

<template>
  <v-form v-model="formIsValid">
    <v-text-field :rules="[required]"></v-text-field>
  </v-form>
</template>

<script>
  data() {
    return {
      formIsValid: false
    }
  },
  methods: {
    required(val) {
      return !!val || 'Required.'
    }
  }
</script>
vuejs2 vuetify.js vue.js
1 Answers

You can explore vuetify source code to learn how they do that.
First, you have to understand provide/inject, https://v2.vuejs.org/v2/api/#provide-inject
A very simplified version of their concept is like below,

VForm.vue

export default {
  data() {
    return {
      inputs: []
    }
  },
  provide () {
    // provide this Form component for child, so child can register itself
    return { form: this }
  },
  methods: {
    register(input) {
      this.inputs.push(input);
    },
    validate() {
      // loop through child registered inputs,
      // run every child.validate() to validate all child
      this.inputs.forEach(input => {
        input.validate();
      });
    }
  }
}

VInput.vue

export default {
  props: {
    rules: {
      default: () => [],
      type: Array
    }
  },
  // inject parent VForm component
  inject: ['form'],
  created() {
    // with inject above, you can use this.form to reference parent VForm
    this.form.register(this);
  },
  methods: {
    validate() {
      // use rules to validate input
    }
  }
}

Usage
anything provide by v-form can be used in v-input with inject.

<template>
  <v-form>
    <v-input :rules="rules"/>
  <v-form/>
</template>

Most of the logic is in these files, and vuetify did much more than the logic above. Learn to study open source code, open source project is awesome.

  1. VForm: https://github.com/vuetifyjs/vuetify/blob/master/packages/vuetify/src/components/VForm/VForm.ts
  2. registrable mixin used by VForm: https://github.com/vuetifyjs/vuetify/blob/master/packages/vuetify/src/mixins/registrable/index.ts
  3. VInput: https://github.com/vuetifyjs/vuetify/blob/master/packages/vuetify/src/components/VInput/VInput.ts
  4. validatable mixin used by VInput: https://github.com/vuetifyjs/vuetify/blob/master/packages/vuetify/src/mixins/validatable/index.ts
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