Javascript 如何克服此错误TypeError:无法读取属性'；孤岛加载'；使用react redux（还原剂）时的未定义值

我已经创建了一个屏幕来显示表中的数据。此屏幕通过actions、sagas和reducer文件连接到redux。当我试图

mapstatetops

还原程序状态的数据时，它会带来以下错误

TypeError:cannotreadproperty'isLoading'of undefined

。假设

isLoading

是状态中的内容之一

下面是react文件上的剪报

<Segment>
              <Table basic="very">
                <Table.Header>
                  <Table.Row>
                    <Table.HeaderCell className="colors">
                      Class
                    </Table.HeaderCell>
                    <Table.HeaderCell className="colors">
                      Streams
                    </Table.HeaderCell>
                    <Table.HeaderCell className="colors">
                      Actions
                    </Table.HeaderCell>
                  </Table.Row>
                </Table.Header>
                <Table.Body>
                  {this.props.tableData.map((data, index) => (
                    <Table.Row key={index} className="colors">
                      <Table.Cell>{data.class}</Table.Cell>
                      <Table.Cell>{data.stream}</Table.Cell>
                      <Table.Cell>
                        <span className="pointer">Statistics</span> |
                        <span className="pointer"> remove</span>
                      </Table.Cell>
                    </Table.Row>
                  ))}
                </Table.Body>
              </Table>
            </Segment>
          </Segment.Group>
        </Grid.Column>
      </Grid>
    </Segment>
  </div>
);
 }
}
  const mapStateToProps = state => {
  const { isLoading, tableData, error } = state.classes;
  return {
   isLoading,
   tableData,
   error
 };
};
 export default connect(mapStateToProps, {
  fetchClassStreamRequest,
  attachRequest,
})(AdminClasses);

---

如需任何帮助，将不胜感激。

在您设置的位置未正确设置isLoading。您的

类

reducer在reducer树中的嵌套程度如何？i、 e.从根减缩器看，它和

类之间有什么关系（
状态？.classes
）？你的
classes
reducer本身看起来不错。你好，谢谢allot Drew，我没有把“classes”reducer放在根reducer中。它现在运行良好。再次感谢
 import { classConstants } from "../constants/classes.constants";
  const data = [
    { class: "s.1", stream: "Red" },
    { class: "s.1", stream: "Red" },
    { class: "s.1", stream: "Red" }
  ];
 const initialState = {
   isLoading: false,
   tableData: data,
   error: ""
 };
 export function classes(state = initialState, action) {
 switch (action.type) {
   case classConstants.FETCH_CLASSSTREAMS_REQUEST:
  return {
    ...state,
    error: ""
  };
  case classConstants.FETCH_CLASSSTREAMS_SUCCESS:
  return {
    ...state,
    error: "",
     tableData: action.payload
  };
  case classConstants.FETCH_CLASSSTREAM_FAILURE:
  return {
    ...state,
    error: "Error in fetching"
  };
default:
      return state;
  }
}