如何在 xamarin 表单中使用异步更改 ui

Question

我尝试以 xamarin 形式开发移动应用程序。我有新闻列表，我正在使用 SQLite 来存储它。当我的主页打开时，在我从 SQLite 获取新闻之前，我尝试从 Web API 获取新新闻。我可以在 SQLite 中保存新消息，但我的 UI 没有改变。我该如何解决？

    public MainPage()
    {
        InitializeComponent();

        database = new Helper.xxxDatabase(Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData), "xxx.db3"));

        SetLocalDBMainNews();

        Task.Run(async () => { await GetNewsAsync(); });
    }
    void SetLocalDBMainNews()
    {
        if(database.TableExists("News"))
        {
            List<News> newsList = database.GetNewsData();
            if (newsList.Count > 0)
            {
                MaiNewsList.ItemsSource = newsList.Where(x => x.Type.Equals((int)NewsType.MainNews)).OrderBy(x => x.Sort).ToList();
            }
        }
        else
            database.CreateNewsTable();
    }
    private async Task GetNewsAsync()
    {
        try
        {
            var register = database.GetRegisterData();
            string url = "http://xxx.azurewebsites.net/api/News/GetPublishedNews";
            var response = Tools.Send(url, "GET", register.Token);
            var result = JsonConvert.DeserializeObject<ApiResponse<List<News>>>(response);
            if (result.HasError == false)
            {
                var newsList = result.Value;
                database.DeleteAllNews();
                foreach(var n in newsList)
                {
                    database.Insert(n);
                }

                MaiNewsList.ItemsSource = newsList.Where(x => x.Type.Equals((int)NewsType.MainNews)).OrderBy(x => x.Sort).ToList();
            }
        }
        catch{}
    }

该代码适用于将新新闻保存到 SQLite，但我无法将新闻异步绑定到 UI。

编辑：

杰森回答后，这是我的代码最新版本 Device.BeginInvokeOnMainThread 解决我的问题。

private async Task GetNewsAsync()
{
    try
    {
        var register = database.GetRegisterData();
        string url = "http://xxx.azurewebsites.net/api/News/GetPublishedNews";
        var response = Tools.Send(url, "GET", register.Token);
        var result = JsonConvert.DeserializeObject<ApiResponse<List<News>>>(response);
        if (result.HasError == false)
        {
            var newsList = result.Value;
            database.DeleteAllNews();
            foreach(var n in newsList)
            {
                database.Insert(n);
            }

            Device.BeginInvokeOnMainThread(() =>
            {
                MaiNewsList.ItemsSource = newsList.Where(x => x.Type.Equals((int)NewsType.MainNews)).OrderBy(x => x.Sort).ToList();
            });
        }
    }
    catch
    {

    }
}

Answer 1

UI 需要使用 BeginInvokeOnMainThread

在 UI 线程上进行更改

Device.BeginInvokeOnMainThread( () =>
{
    MaiNewsList.ItemsSource = newsList.Where(x => x.Type.Equals((int)NewsType.MainNews)).OrderBy(x => x.Sort).ToList();
});

如何在 xamarin 表单中使用异步更改 ui

how to change change ui with async in xamarin forms

c#

sqlite

xamarin

xamarin.forms

visual-studio-mac