我在我的UWP应用中有一个公共的布尔变量,用于显示/隐藏ProgressBar。我在其他地方使用了相同的模式,看起来工作得不错,但是在特定页面上遇到了一个问题,当我在异步调用之后设置布尔值时,它似乎不会在UI中更新(与正常工作的页面相同)。
以下是我的XAML视图:
<Grid Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">
<TextBlock Text="{ x:Bind Vm.IsLoaded }" Margin="112,272,-112,-272"></TextBlock>
</Grid>
对应的代码文件:
public sealed partial class MainPage : Page
{
public MainPageViewModel Vm => DataContext as MainPageViewModel;
public MainPage()
{
this.InitializeComponent();
this.DataContext = new MainPageViewModel();
}
protected override void OnNavigatedTo(NavigationEventArgs e)
{
base.OnNavigatedTo(e);
Vm.GetProjectData();
}
}
以下是我的MainPageViewModel.cs文件
public class MainPageViewModel : ViewModel
{
public ObservableCollection<Project> Projects { get; set; } = new ObservableCollection<Project>();
private bool _isLoaded;
public bool IsLoaded
{
get { return _isLoaded; }
set
{
_isLoaded = value;
OnPropertyChanged();
}
}
public async Task GetProjectData()
{
// If I put `IsLoaded = true;` here it displays `true` in the UI
var projectsResponse = await HttpUtil.GetAsync(StringUtil.ProjectsUrl());
// If I put `IsLoaded = true;` here it still displays `false` in the UI
if (projectsResponse.IsSuccessStatusCode)
{
var projectsResponseString = await projectsResponse.Content.ReadAsStringAsync();
var projects = JsonUtil.SerializeJsonToObject<List<Project>>(projectsResponseString);
foreach (var project in projects)
{
Projects.Add(project);
}
IsLoaded = true;
}
}
}
我的ViewModel.cs文件:
public class ViewModel : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null)
{
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
}
}
无论我把
IsLoaded = true;
放在哪里,它总会触发 OnPropertyChanged()。下面是我的可用代码:
ProjectViewViewModel.cs:
public class ProjectViewViewModel : ViewModel
{
public ObservableCollection<Story> MyData { get; set; } = new ObservableCollection<Story>();
private bool _dataIsLoaded;
public bool DataIsLoaded
{
get { return _dataIsLoaded; }
set
{
_dataIsLoaded = value;
OnPropertyChanged();
}
}
public async Task GetData(Project project)
{
DataIsLoaded = false;
var stringResponse = await HttpUtil.GetAsync(StringUtil.Query(project.Id, "MB"));
if (stringResponse.IsSuccessStatusCode)
{
// Do Stuff
DataIsLoaded = true;
}
}
}
ProjectView.xaml.cs
public sealed partial class ProjectView : Page
{
public Project Project { get; set; }
public bool IsLoaded { get; set; }
public ProjectViewViewModel Vm => DataContext as ProjectViewViewModel;
public ProjectView()
{
this.InitializeComponent();
this.DataContext = new ProjectViewViewModel();
}
protected override void OnNavigatedTo(NavigationEventArgs e)
{
base.OnNavigatedTo(e);
Project = e.Parameter as Project;
Vm.GetData(Project);
}
}
我感觉自己可能忽略了非常明显的一些问题,但是却无法看到树林中的大树而感到烦恼。非常感谢任何帮助!