将响应传递到视图时发生java Nativescript错误

Question

当选择了listview级别（在product.xml中）时，我尝试发送POST请求，并且从响应中我尝试构建另一个listview（在brand.xml中）。我已成功发送POST请求并获得响应。但我未能将回应传递给view。也就是说我无法构建视图。我想问题是我不能正确地发送数据（与级别文本相关），所以我失败了。我收到此错误：***尝试调用虚拟方法“intjave”。lang.Integer。空对象**上的intValue（）。这是我的代码-

产品。xml:

<Label text="{{ category }}"  horizontalAlignment="left" verticalAlignment="center" tap="brand" />

产品。Js:

    exports.brand=function (args) {

    var item =args.object;

     text=item.text;

     getBrand(text);

     };


function getBrand(data) {

    brand.get(data);

        frameModule.topmost().navigate("view/brand/brand");

}

品牌\u视图\u型号：

function BrandViewModel() {

    var viewModel = new Observable({    
    });

    viewModel.get = function (category){
        data = category;

        }

         viewModel.load = function() {

           fetch("http://10.0.2.2:8000/user_signup", {
           method: "POST",
           headers: { "Content-Type": "application/json" },

           body: JSON.stringify({ 

           category: data,

            })

        }).then(function(response) {
           return response.json();
        }).then(function(data) {

            for(var i=0;i<data.length;i++){

            viewModel.push({
                brand: data[i].brand,

            });

           };  

        });

         }

    viewModel.empty = function() {
    while (viewModel.length) {
        viewModel.pop();
    }
};

    return viewModel;
}

function handleErrors(response) {
    if (!response.ok) {
        console.log(JSON.stringify(response));
        throw Error(response.statusText);
    }
    return response;
}

 module.exports = BrandViewModel;

**品牌。js:**

var BrandViewModel = require("../../shared/brand_view_model");

var observableModule = require("data/observable");

var page;

var data;

var brandList = new BrandViewModel([]);  


var pageData = new observableModule.fromObject({
    brandList: brandList
});


exports.loaded = function(args) {
    page = args.object;

    page.bindingContext = pageData;

    brandList.empty();
    brandList.load();


};

品牌。xml:

<Page loaded="loaded">
    <GridLayout>
        <ListView items="{{ brandList }}" >
            <ListView.itemTemplate>
                <Label text="{{ brand }}"  horizontalAlignment="left" verticalAlignment="center" tap="brand" />
            </ListView.itemTemplate>
        </ListView>

    </GridLayout>
</Page>