获取和设置各有两种方式：通过 node 或通过 key。如果需要通过 key 来获取或设置，则必须设置node-key。

<el-tree
  :data="data"
  show-checkbox
  default-expand-all
  node-key="id"
  ref="tree"
  highlight-current
  :props="defaultProps">
</el-tree>

<div class="buttons">
  <el-button @click="getCheckedNodes">通过 node 获取</el-button>
  <el-button @click="getCheckedKeys">通过 key 获取</el-button>
  <el-button @click="setCheckedNodes">通过 node 设置</el-button>
  <el-button @click="setCheckedKeys">通过 key 设置</el-button>
  <el-button @click="resetChecked">清空</el-button>
</div>

<script>
  export default {
    methods: {
      // 编辑回显
      edit(){
      // 获取详情接口
           getRole(this.id).then((res) => {
            this.getRole = res.data
            if (res.code == 200) {
              this.dialogVisible = true
              this.$nextTick(() => {
                if (res.data.menuIds != null) {
                // 将后端接口数据回显到树上的方法
                  this.$refs.tree.setCheckedKeys(res.data.menuIds)
                }
              })
            } else {
              this.$message.error(res.msg)
            }
          })
      },
      getCheckedNodes() {
        console.log(this.$refs.tree.getCheckedNodes());
      },
      getCheckedKeys() {
        console.log(this.$refs.tree.getCheckedKeys());
      },
      // 设置整个节点
      setCheckedNodes() {
        this.$refs.tree.setCheckedNodes([{
          id: 5,
          label: '二级 2-1'
        }, {
          id: 9,
          label: '三级 1-1-1'
        }]);
      },
      // 设置key值
      setCheckedKeys() {
        this.$refs.tree.setCheckedKeys([3]);
      },
      resetChecked() {
        this.$refs.tree.setCheckedKeys([]);
      }
    },

    data() {
      return {
        data: [{
          id: 1,
          label: '一级 1',
          children: [{
            id: 4,
            label: '二级 1-1',
            children: [{
              id: 9,
              label: '三级 1-1-1'
            }, {
              id: 10,
              label: '三级 1-1-2'
            }]
          }]
        }, {
          id: 2,
          label: '一级 2',
          children: [{
            id: 5,
            label: '二级 2-1'
          }, {
            id: 6,
            label: '二级 2-2'
          }]
        }, {
          id: 3,
          label: '一级 3',
          children: [{
            id: 7,
            label: '二级 3-1'
          }, {
            id: 8,
            label: '二级 3-2'
          }]
        }],
        defaultProps: {
          children: 'children',
          label: 'label'
        }
      };
    }
  };
</script>