异步方法不一致地填充 XAML 绑定字段

Question

我有一个由两个不同的模型填充的视图。对于我的应用，这意味着两个不同的 Services 用于获取这些各自模型的数据。

现在数据根本不会填充。我是什么意思？目前，页面加载时仅显示Group.Name。其余的 User 标签不显示。在三个标签显示之前，我必须创建一个按钮来更改 User 绑定对象中的一个字段。

注意： BaseViewModel 继承 INotifyPropertyChanged 和 IPageLifecycleAware。 SetProperty() 在属性更改时引发事件。

查看

<StackLayout Margin="10" VerticalOptions="StartAndExpand">
    <Grid>
        <Label Grid.Row="0" Text="{Binding User.Name}"/>
        <Label Grid.Row="1" Text="{Binding User.Age}"/>
        <Label Grid.Row="2" Text="{Binding User.Occupation}"/>
        <Label Grid.Row="3" Text="{Binding Group.Name}"/>
    </Grid>
</StackLayout>

视图模型

public class ProfileViewModel : BaseViewModel
{
    private IGroupService _groupService;
    private IUserService _userService;
    public ProfileViewModel(IGroupService groupService, IUserService userService)
    {
        _groupService = groupService;
        _userService = userService;
        GetUser();
        GetGroup();
    }

    private async void GetUser()
    {
        var user = await _userService.GetUserAsync();
        User = user;
        SetProfilePhoto();
    }

    private async void GetGroup()
    {
        var group = await _groupService.GetGroupAsync();
        Group = group;
    }

    private void SetProfilePhoto()
    {
        var profilePhotoBytes = User.ProfilePhotoBytes;
        if (profilePhotoBytes == null || profilePhotoBytes.Length == 0)
            ProfilePhoto = ImageSource.FromResource("MyApp.Images.default_profile_picture.png");
        else
            ProfilePhoto = ImageSource.FromStream(() => new MemoryStream(profilePhotoBytes));
    }

    private ImageSource _profilePhoto;
    public ImageSource ProfilePhoto { get => _profilePhoto; set => SetProperty(ref _profilePhoto, value); }

    private User _user;
    public User User { get => _user; set => SetProperty(ref _user, value); 
    }
    private Group _group;
    public Group Group{ get => _group; set => SetProperty(ref _group, value); }
}

型号

public class User: BindableBase
{
    private string _id;
    public string Id { get => _id; set => SetProperty(ref _id, value); }

    private string _name;
    public string Name { get => _name; set => SetProperty(ref _name, value); }

    private string _age;
    public string Age { get => _age; set => SetProperty(ref _age, value); }

    private string _occupation;
    public string Occupation { get => _occupation; set => SetProperty(ref _occupation, value); }

    private byte[] _profilePhotoBytes;
    public byte[] ProfilePhotoBytes { get => _profilePhotoBytes; set => SetProperty(ref _profilePhotoBytes, value); }

    private ImageSource _profilePhoto;
    public ImageSource ProfilePhoto { get => _profilePhoto; set => SetProperty(ref _profilePhoto, value); }
}

public class Group: BindableBase
{
    private string _id;
    public string Id { get => _id; set => SetProperty(ref _id, value); }

    private string _name;
    public string Name { get => _name; set => SetProperty(ref _name, value); }

    private byte[] _groupPhotoBytes;
    public byte[] GroupPhotoBytes { get => _groupPhotoBytes; set => SetProperty(ref _groupPhotoBytes, value); }

    private string _createdUserId;
    public string CreatedUserId { get => _createdUserId; set => SetProperty(ref _createdUserId, value); }

    private DateTime _createdDate;
    public DateTime CreatedDate { get => _createdDate; set => SetProperty(ref _createdDate, value); }
}

Answer 1

问题似乎很简单……

当您将类属性绑定到未实现 INotifyPropertyChanged 接口的 UI 元素时...对那些不反映您的 UI 元素后 UI 元素的属性所做的任何更改都已呈现...

最简单的解决方法是使用

实现您的模型类

INotifyPropertyChanged

界面...

当您使用 Prism 时，这可以通过继承来实现

可绑定基础

类...例如

public class Group : BindableBase
{
    string _id;
    public string Id { get => _id; set => SetProperty(ref _id, value); }
    string _name;
    public string Name { get => _name; set => SetProperty(ref _name, value); }

    public byte[] GroupPhotoBytes { get; set; } //change similarly like above
    public string CreatedUserId { get; set; } // to do 
    public DateTime CreatedDate { get; set; } // to do
}

完成上述更改后...现在您的 UI 将在您的属性更新时更新...

希望对你有帮助