父组件用ref获取子组件数据

子组件
Son/index.vue

子组件的数据和方法一定要记得用defineExpose暴露，不然父组件用ref是获取不到的！！！

<script setup>
import { ref } from "vue";
const sonNum = ref(1);
const changeSon = () => {sonNum.value++;
};defineExpose({sonNum,changeSon,
});
</script><template><div class="son">{{ sonNum }}</div>
</template><style scoped lang="scss">
.son {width: 100px;height: 20px;border: 1px pink solid;
}
</style>

Father/index.vue

<script setup>
import { ref, onMounted, watch, computed } from "vue";import Son from "../Son/index.vue";
const SonRef = ref(null);
let father = ref();
let sonNumInFather = ref(null);
// console.log("SonRef.value", SonRef.value);
onMounted(() => {father.value = SonRef.value.sonNum;console.log("SonRef.value", SonRef.value.sonNum);console.log("SonRef.value", SonRef.value.changeSon);//   sonNumInFather.value = SonRef.value.sonNum;这样写也可以，但是不会是响应式数据，就永远是初始化的1，不会因为点击按钮就++//   用watch可以实现sonNumInFather是响应数据//   watch(//     () => SonRef.value.sonNum,//     () => {//       father.value = SonRef.value.sonNum;//       console.log("hhhhh");//     }//   );//  用computed可以实现sonNumInFather是响应数据sonNumInFather.value = computed(() => {return SonRef.value.sonNum;});
});const FatherChangeSon = () => {SonRef.value.changeSon();
};
</script><template><button @click="FatherChangeSon">son+1</button><Son ref="SonRef"></Son>{{ sonNumInFather }}<!-- 下面这两个都渲染不成功，都不行 --><!-- {{ SonRef.sonNum }} --><!-- {{ father }} -->// 很奇怪这样就可以了，可以正常显示，也不报错{{ SonRef?.sonNum }}
</template><style scoped lang="scss"></style>