OnPropertyChanged未更新xamarin的xzing条形码扫描仪的UI

Question

我在整个应用程序中使用mvvm，数据绑定和属性更改在应用程序中的其他地方都可以工作，但由于某种原因，在我使用XZing条形码扫描仪的视图中，扫描项目后我的视图没有更新。

我习惯于使用XAML ViewModel和Codebehin，但我设置条形码扫描仪的方式只有ViewModel和codebehin/onlone类。所以，也许我错过了一些我不习惯做的简单的事情。

我在下面发布了一些代码，这只是一个没有更新的属性的例子，productsLable.Text的PartName。当页面第一次加载时，它被绑定，并且伪PartName显示正确，但在扫描了一个新项目后，我在ViewModel中更新了ScannedPart，但；得到"；在我设置并调用OnPropertyChanged((之后从未调用；

这在我的应用程序的其他部分运行得很好，但也许我在这里遗漏了一些愚蠢的东西，就像我说的那样，我更愿意在XAML中使用绑定。你看到我可能做错了什么或遗漏了什么吗？

提前谢谢。

public class TimsCustomScanPage : ContentPage
{
ZXingScannerView zxing;
TimsCustomOverlay overlay;
RequestPartsViewModel viewModel;
public TimsCustomScanPage(RequestPartsViewModel viewModel) : base()
{
//Attaching ViewModel
this.viewModel = viewModel;
this.BindingContext = viewModel;
//Scanner found barcode
zxing.OnScanResult += (result) =>
{
// Stop analysis until we navigate away so we don't keep reading barcodes
zxing.IsAnalyzing = false;
//Setting new scanned part
viewModel.ScannedPart = viewModel.Parts.FirstOrDefault();
};
--Some more code--

var productsLabel = new Label()
{
//Text = "Find New Part",
TextColor = Color.Black,
WidthRequest = 150,
HorizontalOptions = LayoutOptions.Start,
VerticalTextAlignment = TextAlignment.Center,
Padding = new Thickness(0, 0, 0, 0),
};
//Binding text property 
productsLabel.SetBinding(Label.TextProperty, "PartName");
productsLabel.BindingContext = viewModel.ScannedPart;
}

ViewModel

public class RequestPartsViewModel : BaseViewModel
{
public ObservableCollection<TimsCategory> Categories { get; set; }
public ObservableCollection<TimsCategory> FavoriteCategories { get; set; }
public ObservableCollection<TimsPart> Parts { get; set; }
public TimsCategory CurrentSelection { get; set; }
public Command LoadItemsCommand { get; set; }
TimsPart scannedPart;
string partName;
int totalRequestedParts;
public RequestPartsViewModel()
{
Title = "Request Parts";
Categories = new ObservableCollection<TimsCategory>(db.Table<TimsCategory>().ToList());
Parts = new ObservableCollection<TimsPart>(db.Table<TimsPart>().ToList());
TotalRequestedParts = 0;
ScannedPart = new TimsPart();
ScannedPart.PartName = "Scan New Part";
ScannedPart.AvailableQuantity = 0;
//Attach parts to categories 
foreach (var item in Categories)
{
int newId = item.CategoryId;
var partsForCategories = Parts.Where(p => p.CategoryId == newId);
var partsForCategoriesCollection = new ObservableCollection<TimsPart>(partsForCategories);
item.Parts = partsForCategoriesCollection;
}

FavoriteCategories = new ObservableCollection<TimsCategory>(Categories.Take(6).ToList());
LoadItemsCommand = new Command(async () => await ExecuteLoadItemsCommand());
}
public TimsPart ScannedPart
{
get
{
return scannedPart;
}
set
{
if (scannedPart != value)
{
scannedPart = value;
OnPropertyChanged("PartName");
OnPropertyChanged("RequestedQuantity");
OnPropertyChanged("AvailableQuantity");
OnPropertyChanged("ScannedPart");
}
}
}

基本视图模型

public class BaseViewModel : INotifyPropertyChanged
{
public SQLiteConnection db = TimsData.database;
bool isBusy = false;
public bool IsBusy
{
get { return isBusy; }
set { SetProperty(ref isBusy, value); }
}
string title = string.Empty;
public string Title
{
get { return title; }
set { SetProperty(ref title, value); }
}
protected bool SetProperty<T>(ref T backingStore, T value,
[CallerMemberName]string propertyName = "",
Action onChanged = null)
{
if (EqualityComparer<T>.Default.Equals(backingStore, value))
return false;
backingStore = value;
onChanged?.Invoke();
OnPropertyChanged(propertyName);
return true;
}
#region INotifyPropertyChanged
public event PropertyChangedEventHandler PropertyChanged;
protected void OnPropertyChanged([CallerMemberName] string propertyName = "")
{
var changed = PropertyChanged;
if (changed == null)
return;
changed.Invoke(this, new PropertyChangedEventArgs(propertyName));
}
#endregion
}

Answer 1

我认为问题在于，您直接绑定到一个属性，然后更改基础对象，而不仅仅是属性。试试这个

productsLabel.SetBinding(Label.TextProperty, "ScannedPart.PartName");
// you already have a BindingContext set for your page that the Label will inherit
// productsLabel.BindingContext = viewModel.ScannedPart;