使用zxing条形码扫描仪时，MVVMCross的后退按钮出现问题。不幸的是，当我按下后退键时，出现错误：Java.Lang.NullPointerException：尝试在空对象引用上调用虚方法'long android.graphics.Paint.getNativeInstance（）'
当我评论metohs scan（）时，我们一切都很好。 有人知道出了什么问题吗？
这是我的片段扫描视图类：
Keyboards > Properties > Events Tab > Information section在我的viewmdoel中，我有一个简单的方法来关闭当前的viewmodel：
public class ScannView : MvxFragmentActivity, IBarcodeFragmentOptions
{
protected ScannViewModel MainViewModel
{
get { return ViewModel as ScannViewModel; }
}
public static ZXingScannerFragment scanFragment;
protected override void OnResume()
{
base.OnResume();
try
{
if (scanFragment == null)
{
scanFragment = new ZXingScannerFragment();
SupportFragmentManager.BeginTransaction()
.Replace(Resource.Id.frameScanner, scanFragment)
.Commit();
}
scan();
}
catch (Exception ex)
{
Debug.WriteLine(ex);
}
}
protected override void OnPause()
{
try
{
scanFragment?.StopScanning();
base.OnPause();
}catch(Exception ex)
{
Console.WriteLine(ex);
}
}
protected override void OnRestart()
{
base.OnRestart();
}
public void ToogleFlashLight(bool on)
{
if (scanFragment != null)
scanFragment.SetTorch(on);
}
public void scan()
{
try
{
// var results = await CrossPermissions.Current.RequestPermissionsAsync(Plugin.Permissions.Abstractions.Permission.Camera);
// var status = results[Plugin.Permissions.Abstractions.Permission.Camera];
// if (status == Plugin.Permissions.Abstractions.PermissionStatus.Granted)
// {
var opts = new MobileBarcodeScanningOptions
{
PossibleFormats = new List<ZXing.BarcodeFormat> {
ZXing.BarcodeFormat.QR_CODE
},
CameraResolutionSelector = availableResolutions => {
foreach (var ar in availableResolutions)
{
Console.WriteLine("Resolution: " + ar.Width + "x" + ar.Height);
}
return null;
}
};
scanFragment?.StartScanning(opts,result =>
{
if (result == null || string.IsNullOrEmpty(result.Text))
{
RunOnUiThread(() => Toast.MakeText(this, "Anulowanie skanowanie", ToastLength.Long).Show());
return;
}
MainViewModel.ScannedCode = result.Text; //ChangePropertyToEmpty();
RunOnUiThread(() => Toast.MakeText(this, "Zeskanowano: " + result.Text, ToastLength.Short).Show());
});
// }
}catch(Exception ex)
{
Debug.WriteLine(ex);
}
}
protected override void OnViewModelSet()
{
MobileBarcodeScanner.Initialize(Application);
base.OnViewModelSet();
SetContentView(Resource.Layout.layout_scann);
}
}