如何从 Android firebase ML-Kit BarcodeScannerProcessor onSuccess 找到上下文并启动新活动

Question

I am using the quickstart-android code provided by google but after many attempts I cam unable to find a context that is not returning null. The BarcodeScannerProcessor is not itself an Activity, so I have attempted to create an instance of the LivePreviewActivity and use that as the context in the intent, but it's null.

The goal is to once a valid barcode is recognized I want to open a new activity that allows a user to verify value and on the push of a button call a webservice to post the barcode to a database via API. I am having a hard time finding a valid context and the app is crashing when it trys to execute the Intent.

Starting at line 97-107:

https://github.com/jamiekeefer/quickstart-android/blob/master/mlkit/app/src/main/java/com/google/firebase/samples/apps/mlkit/java/barcodescanning/BarcodeScanningProcessor.java

        for (int i = 0; i < barcodes.size(); ++i) {
        FirebaseVisionBarcode barcode = barcodes.get(i);
        BarcodeGraphic barcodeGraphic = new BarcodeGraphic(graphicOverlay, barcode);
        graphicOverlay.add(barcodeGraphic);

        System.out.println(barcode.getRawValue());

        if (!barcode.getRawValue().equals("") ) {

            System.out.println("Got the number:" + barcode.getRawValue() + " Context: " + mContext); //OLD SCHOOL DEBUG OUTPUT

            //enter code to start activity

                Intent intent = new Intent(mContext, SendScannedBarcode.class);
                String message = scannedBarcode;
                intent.putExtra(EXTRA_MESSAGE, message);
                mContext.startActivity(intent);
        }


    }

You can back up in the repo to see the instance of the LivePreviewActivity where I trying to get context.

I have tried a number of things and read about Context, Views and Activities and basically have completely confused myself. The only tuts I can find are using Kotlin, which is not helping clarify things.

I appreacite any help in indentifying or contruting a valid Intent from this Context. Thank you.

Answer 1

So I am assuming that in your LivePreviewActivity you are creating an object of the class BarcodeScanningProcessor . What you can do is change the constructor in the BarcodeScanningProcessor class to accept a context and then you pass in your LivePreviewActivity 's context.

This is what the code should look like:

In BarcodeScanningProcessor :

  public BarcodeScanningProcessor(Context context) {
    // Note that if you know which format of barcode your app is dealing with, detection will be
    // faster to specify the supported barcode formats one by one, e.g.
    // new FirebaseVisionBarcodeDetectorOptions.Builder()
    // .setBarcodeFormats(FirebaseVisionBarcode.FORMAT_QR_CODE)
    // .build();
    detector = FirebaseVision.getInstance().getVisionBarcodeDetector();
    this.mContext = context;
}

Then in LivePreviewActivity :

In the particular case of your activity you would do:

  case BARCODE_DETECTION:
          Log.i(TAG, "Using Barcode Detector Processor");
          cameraSource.setMachineLearningFrameProcessor(new BarcodeScanningProcessor(getApplicationContext()));
          break;

Or if you just wanted to create an object of the class you could do: BarcodeScanningProcessor bsp = new BarcodeScanningProcessor(getApplicationContext());

This should now give your BarcodeScanningProcessor class the context of your activity. Now, in BarcodeScanningProcessor , mContext should not be null and will have the context of your activity. I hope this answers your question.

Answer 2

try this create Application class

import android.app.Application;

public class MyApplication  extends Application {
    static MyApplication instance;

    @Override
    public void onCreate() {
        super.onCreate();
        instance=this;
    }

    public static MyApplication getInstance() {
        return instance;
    }
}

Register in manifest file

<application
        ..
        android:name="com.yourpackage.MyApplication"
        ..>
.
.
.
</application>

start activity using this MyApplication.

Intent intent = new Intent(MyApplication.getInstance(), SendScannedBarcode.class);
                String message = scannedBarcode;
                intent.putExtra(EXTRA_MESSAGE, message);
intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
               MyApplication. getInstance().startActivity(intent);

Answer 3

Another way of handling the issue is create new constructor of BarcodeScanningProcessor which takes interface call back and once processing is done pass back result to caller.

   public interface BarcodeUpdateListener {
      @UiThread
      void onBarcodeDetected(Barcode barcode);
   } 


   private BarcodeUpdateListener callback;

   public BarcodeScanningProcessor(BarcodeUpdateListener callback){
      this.callback = callback;
      detector = FirebaseVision.getInstance().getVisionBarcodeDetector();
   } 

Once you get the result pass result to caller

callback.onBarcodeDetected(<Barcode>)

Answer 4

您可以从graphicOverlay获取上下文：

Context context = graphicOverlay.getContext();