MvvmCross Android EditText绑定未更新屏幕

Question

MvvmCross Android EditText绑定未更新屏幕

5

我发现在使用MvvmCross 3.5.1版本时，当启用“不保留活动”开发人员设置时，Mvvm Cross EditText绑定无法正常工作。以下是复现步骤：

Create a new Core & Droid project using the "Getting Started" Mvvm Cross packages from NuGet.
Add the ZXing.Net.Mobile PCL component from NuGet.

Implement the ViewModel:

    public class FirstViewModel : MvxViewModel
    {
        private readonly IMobileBarcodeScanner _mobileBarcodeScanner;

        public FirstViewModel(IMobileBarcodeScanner mobileBarcodeScanner)
        {
            _mobileBarcodeScanner = mobileBarcodeScanner;
        }

        private string _barCode = "";
        public string BarCode
        { 
            get { return _barCode; }
            set { _barCode = value; RaisePropertyChanged(() => BarCode); }
        }

        private MvxCommand _scanBarCodeCommand;
        public IMvxCommand ScanBarCodeCommand
        {
            get
            {
                return _scanBarCodeCommand ?? (_scanBarCodeCommand = new MvxCommand(async () => await OnScanBarCode()));
            }
        }

        private async Task OnScanBarCode()
        {
            var result = await _mobileBarcodeScanner.Scan();
            if (result != null && !string.IsNullOrEmpty(result.Text))
            {
                InvokeOnMainThread(() =>
                {
                    BarCode = result.Text;
                });
            }
        }
    }

Implement the View:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:local="http://schemas.android.com/apk/res-auto"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent">
    <EditText
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        local:MvxBind="Text BarCode" />
    <Button
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Scan"
        local:MvxBind="Click ScanBarCodeCommand" />
</LinearLayout>

Initialize the ZXing.Net.Mobile library in the View:

[Activity(Label = "View for FirstViewModel")]
public class FirstView : MvxActivity
{
    protected override void OnCreate(Bundle bundle)
    {
        base.OnCreate(bundle);
        SetContentView(Resource.Layout.FirstView);
        MobileBarcodeScanner.Initialize(Application);
    }
}

Run the application and scan a bar code. You can use this Barcodesinc bar code generator and scan from your monitor if you don't have any bar codes handy. The scanned bar code should appear in the EditText.

Edit the View XML by adding an android:id to the EditText.

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:local="http://schemas.android.com/apk/res-auto"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent">
    <EditText
        android:id="@+id/scan_text"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        local:MvxBind="Text BarCode" />
    <Button
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Scan"
        local:MvxBind="Click ScanBarCodeCommand" />
</LinearLayout>

Rebuild and run the application. Now the scanned bar code is not displaying in the EditText. The only change was giving the EditText and android:id. Does anyone understand why adding an android:id would break MvvmCross data binding?

- Trevor Balcom

1

如果值不是空字符串，那么只有在设置了ScannedBarCode时会发生什么？ - Giorgi

@Giorgi 这并没有改变任何事情。EditText 在屏幕上仍然是空的。ScannedBarCode 属性仍然保持我扫描的值。就像 ViewModel + View 不同步一样。我已经在上面添加了一个编辑，包含了自我提问以来我学到的更多信息。 - Trevor Balcom

1个回答

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- Martijn00 · Accepted Answer

绑定只针对TextEdit而非EditText进行添加。可以在此处查看实现：https://github.com/MvvmCross/MvvmCross/blob/4.0/Cirrious/Cirrious.MvvmCross.Binding.Droid/MvxAndroidBindingBuilder.cs#L85 您可以按照以下说明添加自定义绑定：

请注意，HTML标记已保留。