如何在 VueJS 中将值从一个子组件传递到另一个子组件？

Question

Full source code: https://github.com/tenzan/menu-ui-tw

Demo: https://flamboyant-euclid-6fcb57.netlify.com/

Goal:

ItemsList and ItemImage are child components to Menu.vue . I need to pass the image_url from ItemsList to ItemImage , in order to change the image on right, after item on left is changed automatically on time intervals.

• Left side: component ItemsList.vue
• Right side: component ItemImage.vue

Component Menu.vue has 2 child components:

<template>
  <div>
    <!-- Two columns -->
    <div class="flex mb-4">
      <div class="w-1/2 bg-gray-400">
        <ItemsList />
      </div>
      <div class="w-1/2 bg-gray-500">
        <ItemImage></ItemImage>
      </div>
    </div>
  </div>
</template>

<script>
import ItemsList from "./ItemsList";
import ItemImage from "./ItemImage";

export default {
  components: {
    ItemsList,
    ItemImage
  }
};
</script>

ItemsList.vue:

<template>
  <div>
    <div v-for="item in menuItems" :key="item.name">
      <ul
        class="flex justify-between bg-gray-200"
        :class="item.highlight ? 'highlight' : ''"
      >
        <p class="px-4 py-2 m-2">
          {{ item.name }}
        </p>
        <p class="px-4 py-2 m-2">
          {{ item.price }}
        </p>
      </ul>
    </div>
  </div>
</template>

<script>
export default {
  data() {
    return {
      menuItems: [
        {
          name: "Apple",
          price: 20,
          image_url: "../assets/images/apple.jpg"
        },
        {
          name: "Orange",
          price: 21,
          image_url: "../assets/images/orange.jpg"
        },
        {
          name: "Banana",
          price: 22,
          image_url: "../assets/images/banana.jpg"
        },
        {
          name: "Grape",
          price: 23,
          image_url: "../assets/images/grape.jpg"
        }
      ]
    };
  },
  created() {
    var self = this;
    self.menuItems.map((x, i) => {
      self.$set(self.menuItems[i], "highlight", false);
    });
    var init = 0;
    setInterval(function() {
      if (init === self.menuItems.length) {
        init = 0;
      }
      self.menuItems[init].highlight = true;
      if (init === 0) {
        self.menuItems[self.menuItems.length - 1].highlight = false;
      } else {
        self.menuItems[init - 1].highlight = false;
      }
      init++;
    }, 2000);
  }
};
</script>

<style scoped>
.highlight {
  background-color: gray;
}
</style>

ItemImage.vue - almost empty

<template>
  <div><p>Hello from ItemImage component</p></div>
</template>

<script>
export default {
  props: ["image_url"]
};
</script>

ItemsList iterates through each item and highlights it. I will need component ItemImage to show an image for that active/highlighted item. URL for an image is item.image_url .

Answer 1

Emit an event in ItemsList component with image_url and in Menu component pass image_url to ItemImage component as a prop. I did this in below codesandbox check it out.

https://codesandbox.io/s/wild-moon-mbto4

Answer 2

You can try with emitting an event from the child to the parent component.

In your child component ItemsList.vue , emit an event to the parent component (where the highlight property is set to true):

created() {
    var self = this;
    self.menuItems.map((x, i) => {
      self.$set(self.menuItems[i], "highlight", false);
    });
    var init = 0;
    setInterval(function() {
      if (init === self.menuItems.length) {
        init = 0;
      }
      self.menuItems[init].highlight = true;

      //emit an event to trigger parent event
      this.$emit('itemIsHighlighted', menuItems[init].image_url)

      if (init === 0) {
        self.menuItems[self.menuItems.length - 1].highlight = false;
      } else {
        self.menuItems[init - 1].highlight = false;
      }
      init++;
    }, 2000);
  }

Then in your parent component Menu.vue :

<ItemsList @itemIsHighlighted="onItemHighlighted"/>
<ItemImage :image_url="this.selectedItem" ></ItemImage>

...

export default {
    data() {
        return {
            selectedItem: '' 
        } 
    }, 
    methods: {
        onItemHighlighted(value) {
            console.log(value) // someValue
            this.selectedItem = value
        }
    }
}

I couldn't test it, but I hope it helps.

You can also check this answer here.

PS Using Vuex would make this task a lot easier.