Xamarin Visual Studio 2017 Java.Lang.ClassNotFoundException：找不到类“BarcodeFragmentActivity”

Question

我正在尝试从片段实例化一个新活动。而且我一直遇到同样的错误。

Java.Lang.ClassNotFoundException：在路径上找不到类“BarcodeFragmentActivity”：DexPathList[[zip 文件“/data/app/StockApp.StockApp-1/base.apk”],nativeLibraryDirectories=[/data/app /StockApp.StockApp-1/lib/arm, /system/fake-libs, /data/app/StockApp.StockApp-1/base.apk!/lib/armeabi-v7a, /system/lib, /vendor/lib] ]

我使用的是 Visual Studio 2017 版本 15.3.3。 我已经到处搜索了这个问题的答案，但无论我尝试了什么，我仍然遇到同样的错误。当我尝试添加

<intent-filter>
    <action android:name="android.intent.action.MAIN" />

    <category android:name="android.intent.category.LAUNCHER" />
</intent-filter>

抛出一个错误，它在构建时找不到 BarcodeFragment。

我的 Android 清单

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android" 
package="StockApp.StockApp" android:versionCode="1" 
android:versionName="1.0" android:installLocation="preferExternal">
    <uses-sdk android:minSdkVersion="23" />
    <uses-permission android:name="android.permission.CAMERA" />
    <application android:allowBackup="true" android:label="@string/app_name" 
android:theme="@style/Theme.AppCompat.Light.DarkActionBar" 
android:supportsRtl="true">
    <activity android:name=".barcodeFragment" android:label="Barcode Fragment"></activity>
    <activity android:name=".barcodeFragmentActivity" android:label="Activity Barcode" android:parentActivityName=".barcodeFragment">
        <meta-data android:name="android.support.PARENT_ACTIVITY" android:value=".barcodeFragmentActivity"></meta-data>
    </activity>
</application>

调用活动的片段：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

using Android;
using Android.App;
using Android.Content;
using Android.Content.PM;
using Android.OS;
using Android.Runtime;
using Android.Views;
using Android.Widget;

using Android.Gms.Vision.Barcodes;
using Android.Gms.Common.Apis;

using Android.Support.V4.View;
using Android.Support.V4.App;
using Android.Support.V7.App;

namespace StockApp
{
    class BarcodeFragment : Android.Support.V4.App.Fragment, View.IOnClickListener
    {
        private CompoundButton autoFocus { get; set; }
        private CompoundButton useFlash { get; set; }
        private Button btnReadBarcode { get; set; }

        private TextView statusMessage { get; set; }
        private TextView barcodeValue { get; set; }

        private static int RC_BARCODE_CAPTURE = 9001;
        private static string TAG = "BarcodeMain";

        public BarcodeFragment() { }

        public void OnClick(View v)
        {
            if (v.Id == Resource.Id.read_barcode)
            {

                Intent intent = new         Intent(Context.ApplicationContext,Activity.ClassLoader.LoadClass("barcodeFragmentActivity"));//("StockApp.StockApp", typeof(BarcodeFragmentActivity));
            //intent.SetClassName("StockApp.StockApp", );
            intent.PutExtra("AutoFocus", autoFocus.Checked);
            intent.PutExtra("UseFlash", useFlash.Checked);

            if (intent.ResolveActivity(Activity.PackageManager) != null)
            {
                StartActivityForResult(intent, RC_BARCODE_CAPTURE);
            }

        }
    }

    public override void OnActivityResult(int requestCode, int resultCode, Intent data)
    {
        if (requestCode == RC_BARCODE_CAPTURE)
        {
            if(resultCode == CommonStatusCodes.Success)
            {
                if(data != null)
                {
                  //  Barcode barcode = data.GetParcelableExtra(BarcodeFragmentActivity.BarcodeObject);
                }
            }
        }
    }

    public override View OnCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
    {
        View view = inflater.Inflate(Resource.Layout.Fragment_BarcodeMain, container, false);
        statusMessage = view.FindViewById(Resource.Id.txtBarcodeStatus) as TextView;
        barcodeValue = view.FindViewById(Resource.Id.txtBarcodeValue) as TextView;

        autoFocus = view.FindViewById(Resource.Id.auto_focus) as CompoundButton;
        useFlash = view.FindViewById(Resource.Id.use_flash) as CompoundButton;

        view.FindViewById(Resource.Id.read_barcode).SetOnClickListener(this);
        btnReadBarcode = view.FindViewById(Resource.Id.read_barcode) as Button;



        return view;
    }

    public static BarcodeFragment newInstance()
    {
        BarcodeFragment fragment = new BarcodeFragment();
        Bundle args = new Bundle();

        fragment.Arguments = args;
        return fragment;
    }
}
}    

我的 BarcodeFragmentActivity 代码：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

using Android;
using Android.App;
using Android.Content;
using Android.OS;
using Android.Runtime;
using Android.Views;
using Android.Widget;
using Android.Content.PM;

using Android.Gms.Vision.Barcodes;
using Android.Gms.Common.Apis;
using Android.Gms.Common;
using Android.Gms.Vision;

using Android.Hardware;

using Android.Support.V4.View;
using Android.Support.V4.App;
using Android.Support.V7.App;
using Android.Support.Design.Widget;

using StockApp.UI;
using StockApp.BarcodeReader;


namespace StockApp
{
    class BarcodeFragmentActivity : AppCompatActivity
    {
    private static string tag = "Barcode-Reader";
    private static int RC_HANDLE_GMS = 9001;
    private static int RC_HANDLE_CAMERA_PERM = 2;

    public static string AutoFocus = "AutoFocus";
    public static string UseFlash = "UseFlash";
    public static string BarcodeObject = "Barcode";


    private CameraSourcePreview<BarcodeGraphic> mPreview;
    private Android.Gms.Vision.CameraSource mCameraSource;
    private GraphicOverlay<BarcodeGraphic> mGraphicOverlay;

    private ScaleGestureDetector scaleGestureDetector;
    private GestureDetector getsureDetector;

    private View layout;
    private static BarcodeFragmentActivity thisInstance;

    protected override void OnCreate(Bundle savedInstanceState)
    {
        thisInstance = this;
        base.OnCreate(savedInstanceState);
        SetContentView(Resource.Layout.Barcode_Capture);

        mPreview = (CameraSourcePreview<BarcodeGraphic>)FindViewById(Resource.Id.preview);
        mGraphicOverlay = (GraphicOverlay<BarcodeGraphic>)FindViewById(Resource.Id.graphicOverlay);

        bool autoFocus = Intent.GetBooleanExtra(AutoFocus, false);
        bool useFlash = Intent.GetBooleanExtra(UseFlash, false);

        int rc = (int) ActivityCompat.CheckSelfPermission(this, Manifest.Permission.Camera);
        if (rc == (int) Permission.Granted)
        {
            createCameraSource(autoFocus, useFlash);
        }
        else
        {
            requestCameraPermission(); 
        }

        getsureDetector = new GestureDetector(this, new CaptureGestureListener());
    }

    private void requestCameraPermission()
    {
        string[] permissions = new string[] { Manifest.Permission.CallPhone };
        if (ActivityCompat.ShouldShowRequestPermissionRationale(this, Manifest.Permission.Camera))
        {

            Snackbar.Make(layout, "Require Camera Permions To Read Barcodes", Snackbar.LengthIndefinite)
                .SetAction("Ok", new Action<View> (delegate(View obj)
                {
                    ActivityCompat.RequestPermissions(this, permissions, RC_HANDLE_CAMERA_PERM);
                }
                    )).Show();
        }
        else
        {
            ActivityCompat.RequestPermissions(this, permissions, RC_HANDLE_CAMERA_PERM);
        }

        //Activity thisActivity = this;
        //View.IOnClickListener listener = new View.IOnClickListener;

    }

    public override bool OnTouchEvent(MotionEvent e)
    {
        bool b = scaleGestureDetector.OnTouchEvent(e);
        bool c = getsureDetector.OnTouchEvent(e);
        return b || c || base.OnTouchEvent(e);
    }

    private void createCameraSource(bool autoFocus, bool useFlash)
    {
        Context context = ApplicationContext;

        BarcodeDetector barcodeDetector = new BarcodeDetector.Builder(context).Build();
        BarcodeTrackerFactory barcodeFactory = new BarcodeTrackerFactory(mGraphicOverlay);
        barcodeDetector.SetProcessor(
            new MultiProcessor.Builder(barcodeFactory).Build());

        if (!barcodeDetector.IsOperational)
        {
            IntentFilter lowstorageFilter = new IntentFilter(Intent.ActionDeviceStorageLow);
            bool hasLowStorage = RegisterReceiver(null, lowstorageFilter) != null;

            if (hasLowStorage)
            {
                Toast.MakeText(this, "Low Storage Error", ToastLength.Long);
            }
        }

        Android.Gms.Vision.CameraSource.Builder builder = new Android.Gms.Vision.CameraSource.Builder(base.ApplicationContext, barcodeDetector)
            .SetFacing(Android.Gms.Vision.CameraFacing.Back)
            .SetRequestedPreviewSize(1600, 1024)
            .SetRequestedFps(15.0f)
            .SetAutoFocusEnabled(true);

        mCameraSource = builder.Build();




    }

    private void startCameraSource()
    {
        int code = GoogleApiAvailability.Instance.IsGooglePlayServicesAvailable(ApplicationContext);

        if(code != ConnectionResult.Success)
        {
            Dialog dig = GoogleApiAvailability.Instance.GetErrorDialog(this, code, RC_HANDLE_GMS);
            dig.Show();
        }

        if (mCameraSource != null)
        {
            try
            {
                mPreview.start(mCameraSource, mGraphicOverlay);
            }
            catch (InvalidOperationException)
            {
                mCameraSource.Release();
                mCameraSource = null;
            }
        }
    }

    private bool OnTap(float rawX, float rawY)
    {
        int[] location = new int[2];
        mGraphicOverlay.GetLocationOnScreen(location);
        float x = (rawX - location[0]);
        float y = (rawY - location[1]);

        Barcode best = null;
        float bestDistance = float.MaxValue;

        foreach (BarcodeGraphic graphic in mGraphicOverlay.getGraphics())
        {
            Barcode barcode = graphic.GetBarcode();

            if(barcode.BoundingBox.Contains((int)x,(int)y))
            {
                best = barcode;
                break;
            }

            float dx = x - barcode.BoundingBox.CenterX();
            float dy = y - barcode.BoundingBox.CenterY();

            float distance = (dx * dx) + (dy * dy);

            if ( distance > bestDistance)
            {
                best = barcode;
                bestDistance = distance;
            }

            if (best != null)
            {
                Intent data = new Intent();
                data.PutExtra(BarcodeObject, best);
                SetResult(CommonStatusCodes.Success, data);
                Finish();
                return true;
            }

        }
        return false;

    }

    protected override void OnResume()
    {
        base.OnResume();
        startCameraSource();
    }

    protected override void OnPause()
    {
        base.OnPause();
        if (mPreview != null)
        {
            mPreview.stop();
        }
    }

    protected override void OnDestroy()
    {
        base.OnDestroy();
        if(mPreview != null)
        {
            mPreview.release();
        }
    }

    private class CaptureGestureListener : GestureDetector.SimpleOnGestureListener
    {
        public override bool OnSingleTapConfirmed(MotionEvent e)
        {
            return thisInstance.OnTap(e.RawX, e.RawY) || base.OnSingleTapConfirmed(e);
        }
    }

    private class ScaleListener : ScaleGestureDetector.IOnScaleGestureListener
    {
        public IntPtr Handle => throw new NotImplementedException();

        public void Dispose()
        {
            throw new NotImplementedException();
        }

        public bool OnScale(ScaleGestureDetector detector)
        {
            return false;
        }

        public bool OnScaleBegin(ScaleGestureDetector detector)
        {
            return true;
        }

        public void OnScaleEnd(ScaleGestureDetector detector)
        {
        }
    }

  }
}

Answer 1

我正在尝试从片段实例化一个新活动。

在你的代码中，我看到了：

Activity.ClassLoader.LoadClass("barcodeFragmentActivity")//("StockApp.StockApp", typeof(BarcodeFragmentActivity));

为什么要使用LoadClass 方法？在您的项目中，您在另一个classes2.dex 中使用MultiDex 和barcodeFragmentActivity？

如果没有，请修改您的代码：

Intent intent = new Intent(Context.ApplicationContext, Activity.ClassLoader.LoadClass("barcodeFragmentActivity"));

到

Intent intent = new Intent(Context.ApplicationContext, typeof(BarcodeFragmentActivity));

它会正常工作的。