无法在React Native中使用`fetch（）`

知道为什么我不能fetch()在React Native中工作吗？完整代码位于RN Play上：https : //rnplay.org/apps/L80w2w

这是我正在尝试在React Native中工作的工作ReactJS小提琴：https ://jsfiddle.net/ssorallen/fEsYt/

componentDidMount: function() {
        var _this = this;
        var queryParams = "fn" + Date.now() + '/';
        var queryUrl = "https://www.reddit.com/reddits.json?jsonp=" + queryParams;

        fetch(queryUrl)
          .then(response => response.json())
          .then(responseData => this._handleResponse(responseData.data.children))
          .catch(error => this.setState({
            isLoading: false,
            errorMessage: 'Something bad happened - loading navigationItems: \n' + error
          }));
    },

    _handleResponse(results) {
        this.setState({ isLoading: false });

        if (results.length > 0) {
            this.setState({
                navigationItems: results
            });
        } else {
          this.setState({ errorMessage: "Can't find JSON." });
        }
    },