What should I do if uniapp $refs cannot be obtained?

In uniapp, $refs is a very important attribute that can be used to obtain component instances. However, sometimes when using $refs to obtain a component instance, it may not be obtained. This article will discuss this issue.

1. What is $refs

$refs is a special attribute in Vue, which can be used to obtain component instances or dom elements. The same applies in uniapp.

We can create a $refs object by adding a ref attribute on the component:

<template>
  <view ref="myComponent"></view>
</template>
<script>
  export default{
    onReady(){
      console.log(this.$refs.myComponent)
    }
  }
</script>

In the above code, we added a ref attribute on the view component and named it "myComponent ". After the component instance is ready, we obtain the component instance through this.$refs.myComponent.

2. Problems that may cause $get

In uniapp, when using $refs of get to obtain component instances, it may not be obtained. The reasons are as follows:

1. Wrong acquisition time

In uniapp, the life cycle of components is very important. If you use $refs to obtain the component instance early in the component life cycle, you may not be able to obtain it. In this case, we can use the uni.nextTick() function to ensure that the acquisition time is correct.

<template>
  <my-component ref="myComponent"></my-component>
</template>
<script>
  export default{
    onReady(){
      uni.nextTick(()=>{
        console.log(this.$refs.myComponent)
      })
    }
  }
</script>

In the above code, we added a ref attribute on the my-component component. After the component instance is ready, we ensure the correctness of the acquisition timing through the uni.nextTick() function.

2. The component does not set the ref attribute

This problem is relatively simple. If the component does not set the ref attribute, then $get cannot obtain the component instance. In this case, we just need to add the ref attribute to solve the problem.

3. Get a non-existent component instance

The $get method returns a component instance. If we pass in a non-existent component instance when calling, $get Methods also cannot return component instances. Therefore, we need to verify the incoming component instance.

<template>
  <my-component ref="myComponent"></my-component>
</template>
<script>
  export default{
    onReady(){
      const myComponent = this.$refs.myComponent;
      if(myComponent){
        console.log(myComponent)
      }else{
        console.error("组件实例不存在")
      }
    }
  }
</script>

In the above code, we first assign myComponent to the obtained component instance, and then judge it. If myComponent exists, the component instance is output; if it does not exist, the error message "Component instance does not exist" is output.

3. Problems that may cause $refs not to be obtained

In addition to problems with the $get method, there are also some factors that may cause $refs to not be able to obtain component instances.

1. $refs are used in templates

The template is part of the component in uniapp, and it can be used inside the component. However, when using $refs inside the template to obtain the component instance, it may not be obtained. This is because the template is generated earlier than the component instance, so if we use $refs inside the template to get the component instance, we will not be able to get it. The way to avoid this problem is to place $refs inside the component instance and use the uni.nextTick() function appropriately.

<template>
  <my-component></my-component>
</template>
<script>
  export default{
    components:{
      myComponent:{
        template:`
        <view ref="myComponent"></view>
        `,
        onReady(){
          uni.nextTick(()=>{
            console.log(this.$refs.myComponent)
          })
        }
      }
    }
  }
</script>

In the above code, we define a view component inside the my-component component and add the ref attribute. After the view component instance is ready, we ensure the correctness of the acquisition timing through the uni.nextTick() function.

2. The problem of data transfer between parent component and child component

In uniapp, the component instance can obtain the data passed by the parent component through the props attribute. Therefore, if we use $refs in the parent component to obtain the child component instance, but the child component does not set the ref attribute, then $refs will not be able to obtain the child component instance.

//子组件
<template>
  <view>这是一个子组件</view>
</template>
<script>
  export default{
    props:['msg']
  }
</script>

//父组件
<template>
  <my-component/>
</template>
<script>
  export default{
    components:{
      myComponent:{
        template:`
        <child-component></child-component>
        `,
        onReady(){
          console.log(this.$refs.childComponent)    //获取不到子组件实例
        }
      }
    }
  }
</script>

In the above code, we use $refs in the parent component to obtain the child component instance, but the child component does not set the ref attribute. Therefore, we cannot get the child component instance. To solve this problem, we can add the ref attribute in the child component and pass it to the parent component.

//子组件
<template>
  <view>这是一个子组件</view>
</template>
<script>
  export default{
    props:['msg'],
    mounted(){
      this.$emit("getChild",this)       //将子组件实例传递给父组件
    }
  }
</script>

//父组件
<template>
  <my-component @getChild="getChild"/>
</template>
<script>
  export default{
    components:{
      myComponent:{
        template:`
        <child-component ref="childComponent"></child-component>
        `,
        methods:{
          getChild(instance){
            console.log(instance.$el)      //获取到子组件的el元素
            console.log(this.$refs.childComponent)    //获取到子组件实例
          }
        }
      }
    }
  }
</script>

In the above code, we define a mounted cycle in the child component, during which we pass the child component instance to the parent component through this.$emit(). The parent component obtains the child component instance through the ref attribute of the child component.

4. Summary

$ref is a very important attribute in uniapp, which can be used to obtain component instances and dom elements. When using $refs, we need to pay attention to the following points:

1. The acquisition timing must be correct;
2. The component needs to set the ref attribute;
3. The component instance needs to be correct Pass;
4. You need to use the uni.nextTick() function when necessary.

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