第一步：在build.gradle添加依賴原件

dependencies {
...
implementation 'com.google.android.gms:play-services-vision:16.2.0'
}

第二步：在你的布局文件xml上增加一個TextView 和一個SurfaceView

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <SurfaceView
        android:id="@+id/surfaceView"
        android:layout_width="301dp"
        android:layout_height="281dp"
        android:layout_marginTop="48dp"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <TextView
        android:id="@+id/textView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Hello World!"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

</androidx.constraintlayout.widget.ConstraintLayout>

第三步：定義需要的原件、相機、Google的Vision套件

SurfaceView surfaceView;
TextView textView;
CameraSource cameraSource;      //相機
BarcodeDetector barcodeDetector;//Google的Vision套件

第四步：使用套件

barcodeDetector = new BarcodeDetector.Builder(this)
.setBarcodeFormats(Barcode.QR_CODE).build();
cameraSource=new CameraSource.Builder(this,barcodeDetector)
.setRequestedPreviewSize(300,300).build();

第四步：使用surfaceView 來顯示

surfaceView.getHolder().addCallback(new SurfaceHolder.Callback(){
            @Override
            public void surfaceCreated(@NonNull SurfaceHolder surfaceHolder) {
                if(ActivityCompat.checkSelfPermission(getApplicationContext(), Manifest.permission.CAMERA)
                        != PackageManager.PERMISSION_GRANTED)
                    return;
                try{
                    cameraSource.start(surfaceHolder);
                }catch (IOException e){
                    e.printStackTrace();
            }
        }

            @Override
            public void surfaceChanged(@NonNull SurfaceHolder surfaceHolder, int i, int i1, int i2) {

            }

            @Override
            public void surfaceDestroyed(@NonNull SurfaceHolder surfaceHolder) {
              cameraSource.stop();
            }
    });

之後再將關閉相機的程式碼打在 surfaceView 下的 surfaceDestroyed 就可以了

cameraSource.stop();

*可以只打以下代碼之後按 Alt+Enter自動生成 *

surfaceView.getHolder().addCallback(new SurfaceHolder.Callback(){
});

第五步：開始讀寫條碼

barcodeDetector.setProcessor(new Detector.Processor<Barcode>(){

            @Override
            public void release() {
            }
            @Override
            public void receiveDetections(Detector.Detections<Barcode> detections) {
                final SparseArray<Barcode> qrCodes=detections.getDetectedItems();
                if(qrCodes.size()!=0){
                    textView.post(new Runnable() {
                        @Override
                        public void run() {
                            textView.setText(qrCodes.valueAt(0).displayValue);
                        }
                    });
            }
        }
    });

最後即可顯示到你的textview 上了