In Vue 2.0 the documentation and others clearly indicate that communication from parent to child happens via props.
How does a parent tell its child an event has happened via props?
Should I just watch a prop called event? That doesn't feel right, nor do alternatives ( $emit
/ $on
is for child to parent, and a hub model is for distant elements).
I have a parent container and it needs to tell its child container that it's okay to engage certain actions on an API. I need to be able to trigger functions.
Give the child component a ref
and use $refs
to call a method on the child component directly.
html:
<div id="app">
<child-component ref="childComponent"></child-component>
<button @click="click">Click</button>
</div>
javascript:
var ChildComponent = {
template: '<div>{{value}}</div>',
data: function () {
return {
value: 0
};
},
methods: {
setValue: function(value) {
this.value = value;
}
}
}
new Vue({
el: '#app',
components: {
'child-component': ChildComponent
},
methods: {
click: function() {
this.$refs.childComponent.setValue(2.0);
}
}
})
For more info, see Vue documentation on refs .
What you are describing is a change of state in the parent. You pass that to the child via a prop. As you suggested, you would watch
that prop. When the child takes action, it notifies the parent via an emit
, and the parent might then change the state again.
var Child = { template: '<div>{{counter}}</div>', props: ['canI'], data: function () { return { counter: 0 }; }, watch: { canI: function () { if (this.canI) { ++this.counter; this.$emit('increment'); } } } } new Vue({ el: '#app', components: { 'my-component': Child }, data: { childState: false }, methods: { permitChild: function () { this.childState = true; }, lockChild: function () { this.childState = false; } } })
<script src="//cdnjs.cloudflare.com/ajax/libs/vue/2.2.1/vue.js"></script> <div id="app"> <my-component :can-I="childState" v-on:increment="lockChild"></my-component> <button @click="permitChild">Go</button> </div>
If you truly want to pass events to a child, you can do that by creating a bus (which is just a Vue instance) and passing it to the child as a prop .
You can use $emit
and $on
. Using @RoyJ code:
html:
<div id="app">
<my-component></my-component>
<button @click="click">Click</button>
</div>
javascript:
var Child = {
template: '<div>{{value}}</div>',
data: function () {
return {
value: 0
};
},
methods: {
setValue: function(value) {
this.value = value;
}
},
created: function() {
this.$parent.$on('update', this.setValue);
}
}
new Vue({
el: '#app',
components: {
'my-component': Child
},
methods: {
click: function() {
this.$emit('update', 7);
}
}
})
Running example: https://jsfiddle.net/rjurado/m2spy60r/1/
A simple decoupled way to call methods on child components is by emitting a handler from the child and then invoking it from parent.
var Child = { template: '<div>{{value}}</div>', data: function () { return { value: 0 }; }, methods: { setValue(value) { this.value = value; } }, created() { this.$emit('handler', this.setValue); } } new Vue({ el: '#app', components: { 'my-component': Child }, methods: { setValueHandler(fn) { this.setter = fn }, click() { this.setter(70) } } })
<script src="https://cdn.jsdelivr.net/npm/vue@2.5.17/dist/vue.js"></script> <div id="app"> <my-component @handler="setValueHandler"></my-component> <button @click="click">Click</button> </div>
The parent keeps track of the child handler functions and calls whenever necessary.
Did not like the event-bus approach using $on
bindings in the child during create
. Why? Subsequent create
calls (I'm using vue-router
) bind the message handler more than once--leading to multiple responses per message.
The orthodox solution of passing props down from parent to child and putting a property watcher in the child worked a little better. Only problem being that the child can only act on a value transition. Passing the same message multiple times needs some kind of bookkeeping to force a transition so the child can pick up the change.
I've found that if I wrap the message in an array, it will always trigger the child watcher--even if the value remains the same.
Parent:
{
data: function() {
msgChild: null,
},
methods: {
mMessageDoIt: function() {
this.msgChild = ['doIt'];
}
}
...
}
Child:
{
props: ['msgChild'],
watch: {
'msgChild': function(arMsg) {
console.log(arMsg[0]);
}
}
}
HTML:
<parent>
<child v-bind="{ 'msgChild': msgChild }"></child>
</parent>
如果你有时间,可以使用 Vuex 存储来观察变量(又名状态)或直接触发(又名调度)一个动作。
The below example is self explainatory. where refs and events can be used to call function from and to parent and child.
// PARENT
<template>
<parent>
<child
@onChange="childCallBack"
ref="childRef"
:data="moduleData"
/>
<button @click="callChild">Call Method in child</button>
</parent>
</template>
<script>
export default {
methods: {
callChild() {
this.$refs.childRef.childMethod('Hi from parent');
},
childCallBack(message) {
console.log('message from child', message);
}
}
};
</script>
// CHILD
<template>
<child>
<button @click="callParent">Call Parent</button>
</child>
</template>
<script>
export default {
methods: {
callParent() {
this.$emit('onChange', 'hi from child');
},
childMethod(message) {
console.log('message from parent', message);
}
}
}
</script>
Calling child component in parent
<component :is="my_component" ref="my_comp"></component>
<v-btn @click="$refs.my_comp.alertme"></v-btn>
in Child component
mycomp.vue
methods:{
alertme(){
alert("alert")
}
}
我认为我们应该考虑一下 parent 使用 child 的方法的必要性。实际上,父母不必关心 child 的方法,而是可以将 child 组件视为 FSA(finite state machine)。Parents 组件控制子组件的状态。所以观察状态变化或只使用计算功能的解决方案就足够了
You could use a mixin to set a shared data attribute. Change it in the parent, watch it in the child:
// mixin
export default {
data() {
return {
clicked: false
}
}
}
// parent
export default {
mixins: [myMixin],
methods: {
btnClick() {
this.clicked = true
}
}
}
// child
export default {
mixins: [myMixin],
watch: {
clicked(val) {
if(val) {
// yay
}
}
}
}
you can use key to reload child component using key
<component :is="child1" :filter="filter" :key="componentKey"></component>
If you want to reload component with new filter, if button click filter the child component
reloadData() {
this.filter = ['filter1','filter2']
this.componentKey += 1;
},
and use the filter to trigger the function
You can simulate sending event to child by toggling a boolean prop in parent.
Parent code :
...
<child :event="event">
...
export default {
data() {
event: false
},
methods: {
simulateEmitEventToChild() {
this.event = !this.event;
},
handleExample() {
this.simulateEmitEventToChild();
}
}
}
Child code :
export default {
props: {
event: {
type: Boolean
}
},
watch: {
event: function(value) {
console.log("parent event");
}
}
}
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