在xamarin.forms json中使用web服務

Question

我想在按鈕名稱和圖像徽標上的列表視圖中顯示源的值，因為我已經綁定了圖像源和名稱。 但是似乎沒有顯示結果。

public async Task<string> GetRequest (string url){
    Uri geturi = new Uri("http://172.20.129.193/nypstudentlifeservice/"); 
    HttpClient client = new HttpClient();
    HttpResponseMessage responseGet = await client.GetAsync(geturi);
    return responseGet.Content.ReadAsStringAsync().Result;
}

public async Task<IEnumerable<CsClubList>> getClubList()
{
    string result = await GetRequest("api/club/list?categoryid=2");

    CsClubList[] clublist = null;

    var clubtoken = JObject.Parse(result)[0];

    clublist = clubtoken.Select(clublists => new CsClubList()
    {
        Id = (int)clublists["Id"],
        Name = (string)clublists["Name"],
        Logo = (string)clublists["Logo"],
        CategoryId = (int)clublists["CategoryId"]
    }).ToArray();

    return clublist;
}

這是我嘗試使用Json Web服務的代碼。

這是CsClubList的類文件

public class CsClubList
{
    public int Id{ get; set;}
    public int CategoryId { get; set; }
    public string Name {get; set;}
    public string Logo {get; set;}
}

對於xaml.cs文件

public partial class ListClubs : ContentPage
{
    private IEnumerable<CsClubList> _ClubList;

    public ListClubs ()
    {
         InitializeComponent();
         setClubs(Clublistview); //The statement is not awaited and execution of current method continues before the call is complete. Consider using 'await' operator or calling 'Wait' method
    }


    public IEnumerable<CsClubList> ClubList 
    {
        get { return _ClubList; }
        set { _ClubList = value; }
    }

    private async void setClubs(ListView listview)
    {
        ClubApiClient service = new ClubApiClient();
        var clublist = await service.getClubList();
        listview.ItemsSource = clublist.ToList();
    }
}

這是xaml頁面：

<ListView  x:Name="Clublistview">
        <ListView.ItemTemplate>
            <DataTemplate>
                <ViewCell>
                    <StackLayout BackgroundColor="White"
                    Orientation="Vertical">
                        <StackLayout Orientation="Horizontal">
                            <Image Source="{Binding Logo}" IsVisible="true" WidthRequest="42" HeightRequest="42"/>
                             <Button Text="{Binding Name}" x:Name="BtnClub" AbsoluteLayout.LayoutBounds="100, 25, 100, 25" Clicked="OnListClubsClicked" TextColor="Black" VerticalOptions="FillAndExpand"/>
                        </StackLayout>
                    </StackLayout>
                </ViewCell>
            </DataTemplate>
        </ListView.ItemTemplate>
    </ListView>

這是Json Web服務的鏈接：

http://172.20.129.193/nypstudentlifeservice/api/club/list?categoryid=2

[{"Id":21,"CategoryId":2,"Name":"Chinese Cultural Group","Logo":"http://www.nyp.edu.sg/web/campus_life/cca/arts_&_culture/image/CCG2.png"},{"Id":22,"CategoryId":2,"Name":"Chinese Orchestra","Logo":"http://www.nyp.edu.sg/web/campus_life/cca/arts_&_culture/image/CO-ICON.png"},{"Id":23,"CategoryId":2,"Name":"Dance Company","Logo":"http://www.nyp.edu.sg/web/campus_life/cca/arts_&_culture/image/DC2.png"},{"Id":24,"CategoryId":2,"Name":"Danz Inc.","Logo":"http://www.nyp.edu.sg/web/campus_life/cca/arts_&_culture/image/DI-ICON.png"},{"Id":25,"CategoryId":2,"Name":"Der Treff German Club","Logo":"http://www.nyp.edu.sg/web/campus_life/cca/arts_&_culture/image/DTG-ICON.png"},{"Id":26,"CategoryId":2,"Name":"Foreign Bodies Dance Group","Logo":"http://www.nyp.edu.sg/web/campus_life/cca/arts_&_culture/image/FB-ICON.png"}]

Answer 1

您還沒有真正說明問題是什么或您的問題是什么，但這里有一些基於您提供的代碼的觀察。

您正在代碼中混合異步和同步調用。 不要在異步方法中使用.Result或.Wait 。

從您嘗試以字符串形式讀取響應的行中刪除.Result ，並像處理HTTP請求一樣await結果。

還注意到您沒有正確構建Uri以滿足您的要求。 您使用基址創建了一個Uri，但未包含提供的url參數。

public async Task<string> GetRequest(string url) {
    Uri getUri = new Uri("http://172.20.129.193/nypstudentlifeservice/" + url);
    HttpClient client = new HttpClient();
    HttpResponseMessage responseGet = await client.GetAsync(getUri);
    responseGet.EnsureSuccessStatusCode(); // Throw if not a success code.
    string content = await responseGet.Content.ReadAsStringAsync();
    return content;
}

public async Task<IEnumerable<CsClubList>> getClubList() {
    string json = await GetRequest("api/club/list?categoryid=2");

    List<CsClubList> clublist = JsonConvert.DeserializeObject<List<CsClubList>>(json);

    return clublist;
}

除非它們是事件處理程序，否則您還應盡可能在void方法上使用async。

所以，如果可能的話，你需要改變它

//NO NO NO NO NO
private async void setClubs(ListView listview)
{
    ClubApiClient service = new ClubApiClient();
    var clublist = await service.getClubList();
    listview.ItemsSource = clublist.ToList();
}

對此

private async Task setClubs(ListView listview)
{
    ClubApiClient service = new ClubApiClient();
    var clublist = await service.getClubList();
    listview.ItemsSource = clublist.ToList();
}