Xamarin Android Webview：getUserMedia 无法打开相机

Question

我正在尝试打开相机并允许用户从 Xamarin.Android 的 web 视图中捕获图像帧。

我已将 webview 指向此 URL，其中包含一些示例：https://googlechrome.github.io/samples/image-capture/index.html。在设备的 Chrome 浏览器中打开 URL 时，这些示例运行良好，但在应用程序的 web 视图中打开时失败。这是我的 WebChromeClient 实现：

internal class ChromeWebviewClient : WebChromeClient
{
    public override void OnPermissionRequest(PermissionRequest request)
    {
            request.Grant(request.GetResources());
    }
}

我已在清单中声明了相机权限：

<uses-permission android:name="android.permission.CAMERA" />

导航到示例页面并点击“获取用户媒体”似乎没有任何作用，我在应用程序日志中看到以下似乎相关但对我没有意义的内容：

[CameraManagerGlobal] Connecting to camera service
[VendorTagDescriptor] addVendorDescriptor: vendor tag id 3854507339 added
[CameraManagerGlobal] Camera 0 facing CAMERA_FACING_BACK state now CAMERA_STATE_CLOSED for client com.masterappstudio.qrcodereader API Level 1
[CameraManagerGlobal] Camera 1 facing CAMERA_FACING_FRONT state now CAMERA_STATE_CLOSED for client com.sec.android.app.sbrowser API Level 2
[CameraManagerGlobal] Camera 2 facing CAMERA_FACING_FRONT state now CAMERA_STATE_CLOSED for client android.system API Level 2
[CameraManagerGlobal] Camera 90 facing CAMERA_FACING_FRONT state now CAMERA_STATE_CLOSED for client com.samsung.android.server.iris API Level 2

我还在 OnPermissionRequest 处放置了一个断点，但它似乎没有触发。

我怀疑这与 Android 6+ 中引入的运行时相机权限有关（我运行的是 Android 9）。我已经在手机设置中将相机权限设置为允许，但似乎也没有做任何事情。

我已经在这个主题上用尽了谷歌搜索（大部分点击都围绕着标志性和 phonegap 框架），并注意到这里有一些针对原生 Android 的问题以 0 个答案回应了这个问题。

Answer 1

首先，在 AndroidManifeast.xml 中添加这些权限

<uses-permission android:name="android.permission.CAMERA" />
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.RECORD_AUDIO" />
<uses-permission android:name="android.permission.MODIFY_AUDIO_SETTINGS" />

如果在Android 6.0或以上版本上部署应用，需要在运行时请求权限。

 private void checkpermission()
    {
        if (ContextCompat.CheckSelfPermission(this, Manifest.Permission.Camera) == (int)Permission.Granted)
        {
            // We have permission, go ahead and use the camera.              
        }
        else
        {
            // Camera permission is not granted. If necessary display rationale & request.
            ActivityCompat.RequestPermissions(this, new String[] { Manifest.Permission.Camera }, 1);               
        }
    }

要加载一个 URL，子类 Android.Webkit.WebViewClient 并覆盖 ShouldOverriderUrlLoading 方法。

 public class HelloWebViewClient : WebViewClient
{
    // For API level 24 and later
    public override bool ShouldOverrideUrlLoading(WebView view, IWebResourceRequest request)
    {
        view.LoadUrl(request.Url.ToString());
        return false;
    }
}

然后创建自定义 WebChromeClient 以覆盖 OnPermissionRequest 方法以授予请求。

 public class MyWebChromeClient : WebChromeClient
{
    Activity mActivity = null;
    public MyWebChromeClient(Activity activity)
    {
        mActivity = activity;
    }
    public override void OnPermissionRequest(PermissionRequest request)
    {
        mActivity.RunOnUiThread(() => {
            request.Grant(request.GetResources());
        });
    }
}

 public class MainActivity : AppCompatActivity
{
    private WebView webview1;
    protected override void OnCreate(Bundle savedInstanceState)
    {
        base.OnCreate(savedInstanceState);
        Xamarin.Essentials.Platform.Init(this, savedInstanceState);
        // Set our view from the "main" layout resource
        SetContentView(Resource.Layout.activity_main);
        webview1 = FindViewById<WebView>(Resource.Id.webView1);
        webview1.Settings.JavaScriptEnabled = true;
        webview1.Settings.AllowFileAccessFromFileURLs = true;
        webview1.Settings.AllowUniversalAccessFromFileURLs = true;
        webview1.SetWebViewClient(new HelloWebViewClient());
        webview1.SetWebChromeClient(new MyWebChromeClient(this));
        checkpermission();
    }

    private void checkpermission()
    {
        if (ContextCompat.CheckSelfPermission(this, Manifest.Permission.Camera) == (int)Permission.Granted)
        {
            // We have permission, go ahead and use the camera.
            webview1.LoadUrl("https://googlechrome.github.io/samples/image-capture/index.html");
        }
        else
        {
            // Camera permission is not granted. If necessary display rationale & request.
            ActivityCompat.RequestPermissions(this, new String[] { Manifest.Permission.Camera }, 1);
            webview1.LoadUrl("https://googlechrome.github.io/samples/image-capture/index.html");
        }
    }
    public override void OnRequestPermissionsResult(int requestCode, string[] permissions, [GeneratedEnum] Android.Content.PM.Permission[] grantResults)
    {
        Xamarin.Essentials.Platform.OnRequestPermissionsResult(requestCode, permissions, grantResults);

        base.OnRequestPermissionsResult(requestCode, permissions, grantResults);
    }
}