Xamarin.Android Camera Permissions with ZXing.Net.Mobile 仅在应用重启后有效

Posted 2023-02-19

【中文标题】Xamarin.Android Camera Permissions with ZXing.Net.Mobile 仅在应用重启后有效

【英文标题】：Xamarin.Android Camera Permissions with ZXing.Net.Mobile only works after app restart

【发布时间】：2021-12-13 15:48:52

【问题描述】：

我在 Xamarin.Forms 项目中使用 ZXing.Net.Mobile。它在 ios 上运行良好，但在 android 上，当我第一次使用扫描仪时，我会弹出相机权限并授予它们。

在权限之后没有立即从相机中获取图像。如果我退出应用程序并重新启动，相机从那时起就可以正常工作。我怎样才能让它立即工作？即使我关闭视图、处理并重新初始化它，它仍然无法工作，直到应用重新启动。

这里是相关代码：

public partial class CEUScanModalPage : ContentPage, INotifyPropertyChanged 
    private bool _isScanning;

    public CEUScanModalPage() 
        InitializeComponent();
        IsScanning = false;
        BindingContext = this;
        Indicator.Start();
    

    public bool IsScanning 
        get 
            return _isScanning;
        
        set 
            _isScanning = value;
            OnPropertyChanged();
        
    

    private async void OnCloseButtonClicked(object sender, EventArgs args) 
        await Navigation.PopModalAsync();
    

    protected override void OnAppearing() 
        base.OnAppearing();
        IsScanning = true;
    

    protected override void OnDisappearing() 
        base.OnDisappearing();
        _scanView.OnScanResult -= Handle_OnScanResult;
        _scanView.IsAnalyzing = false;
        _scanView.IsScanning = false;
        ParentGrid.Children.Remove(_scanView);
        _scanView = null;
    

    public async void Handle_OnScanResult(Result result) 
        IsScanning = false;

      
    

XAML：

<?xml version="1.0" encoding="UTF-8" ?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms" xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml" xmlns:local="clr-namespace:BehaviorLive" xmlns:grial="clr-namespace:UXDivers.Grial;assembly=UXDivers.Grial" xmlns:ffimageloading="clr-namespace:FFImageLoading.Forms;assembly=FFImageLoading.Forms" xmlns:fftransformations="clr-namespace:FFImageLoading.Transformations;assembly=FFImageLoading.Transformations" xmlns:zxing="clr-namespace:ZXing.Net.Mobile.Forms;assembly=ZXing.Net.Mobile.Forms"

    x:Class="BehaviorLive.Views.CEUScanModalPage"
                NavigationPage.HasNavigationBar="False"
    Style=" StaticResource MainMenuOrModalBackgroundStyle ">
    <ContentPage.Resources>
        <ResourceDictionary
            Source="/Styles/TabControl/SimpleTabResources.xaml" />
    </ContentPage.Resources>

    <ContentPage.Content>
        <Grid>
            <Grid.RowDefinitions>
                <RowDefinition
                    Height="145" />
                <RowDefinition
                    Height="*" />
            </Grid.RowDefinitions>

            <Grid
                RowSpacing="0"
                ColumnSpacing="0"
                Margin="0,0,0,10"
                VerticalOptions="EndAndExpand">
                <Grid.RowDefinitions>
                    <RowDefinition
                        Height="10" />
                    <RowDefinition
                        Height="Auto" />
                    <RowDefinition
                        Height="Auto" />
                </Grid.RowDefinitions>

                <Grid.ColumnDefinitions>
                    <ColumnDefinition
                        Width="120" />
                    <ColumnDefinition
                        Width="*" />
                </Grid.ColumnDefinitions>

                <!-- LOGO -->
                <Label
                    Grid.Row="0"
                    Grid.RowSpan="3"
                    Margin="20,0"
                    TextColor=" DynamicResource InverseTextColor "
                    FontSize="74"
                     FontFamily="StaticResource FontAwesomeSolid"
                    Text=" x:Static local:FontawesomeSolidFont.Qrcode "
                    Style=" StaticResource FontIcon "
                    HorizontalOptions="Start"
                    VerticalTextAlignment="Center" />

                <!-- WELCOME -->
                <Label
                    Grid.Row="1"
                    Grid.Column="1"
                    Text="CEU Checkin"
                    FontSize="22"
                    TextColor=" DynamicResource InverseTextColor "
                    Style=" StaticResource LabelBoldStyle "
                    VerticalOptions="End"
                    HorizontalOptions="Start" />

                <!-- SUB -->
                <Label
                    Grid.Row="2"
                    Grid.Column="1"
                    Text="Scan QR Code to check in/out of your event"
                    FontSize="16"
                    TextColor=" DynamicResource InverseTextColor "
                    VerticalOptions="Start"
                    HorizontalOptions="Start" />
            </Grid>

            <Grid
                Grid.Row="1"
                BackgroundColor=" DynamicResource MainWrapperBackgroundColor "
                grial:Effects.ApplyIOSSafeAreaAsPadding="Bottom" x:Name="ParentGrid">
                <!-- TAB -->

                <StackLayout x:Name="LoadingIndicator" Grid.Row="0" VerticalOptions="CenterAndExpand">
                    <local:CustomActivityIndicator
                        Grid.Row="0"

                        x:Name="Indicator"
                        HorizontalOptions="Center"
                        VerticalOptions="Start" />

                    <Label
                        Grid.Row="1"
                        FontSize="Large"
                        HorizontalTextAlignment="Center"
                        Text=" grial:Translate StringLoading " />
                </StackLayout>

                <zxing:ZXingScannerView Grid.Row="0" Grid.RowSpan="2" x:Name="_scanView" OnScanResult="Handle_OnScanResult" IsScanning="Binding IsScanning"
                                WidthRequest="200" HeightRequest="200" />




            </Grid>

            <!-- CLOSE ICON -->
            <Label
                Style="StaticResource IconCloseLabelStyle">
                <Label.GestureRecognizers>
                    <TapGestureRecognizer
                        Tapped="OnCloseButtonClicked" />
                </Label.GestureRecognizers>
            </Label>

        </Grid>
    </ContentPage.Content>
</ContentPage>

MainActivity.cs

  public override void OnRequestPermissionsResult(int requestCode, string[] permissions, [GeneratedEnum] Permission[] grantResults) 
        Xamarin.Essentials.Platform.OnRequestPermissionsResult(requestCode, permissions, grantResults);

        base.OnRequestPermissionsResult(requestCode, permissions, grantResults);
    

【问题讨论】：

你用的是什么版本的Zxing？

在调用 ZXing 之前检查/提示权限

@Jason 在我的视图中调用它之前，还是在我在 MainActivity 中调用 Init() 之前？

在你使用它的页面中

【参考方案1】：

解决问题的最佳方法是自己处理权限部分

通用权限助手：

using System.Threading.Tasks;
using Xamarin.Essentials;
using static Xamarin.Essentials.Permissions;

public static async Task<PermissionStatus> CheckAndRequestPermissionAsync<TPermission>()
        where TPermission : BasePermission, new()
    
        TPermission permission = new TPermission();
        var status = await permission.CheckStatusAsync();
        if (status != PermissionStatus.Granted)
        
            status = await permission.RequestAsync();
        

        return status;
    

然后像这样使用它

var status = await PermissionsHelper.CheckAndRequestPermissionAsync<Permissions.Camera>();
if(status != PermissionStatus.Granted)

    return;

【讨论】：

谢谢。我想不出一种方法让它在我的页面中工作，但是在这个页面作为模式呈现之前把它放在页面中似乎可以解决问题。谢谢！

乐于助人:)