How to scan QRCode in android

try {
    Intent intent = new Intent("com.google.zxing.client.android.SCAN");
    intent.putExtra("SCAN_MODE", "QR_CODE_MODE"); // "PRODUCT_MODE for bar codes

    startActivityForResult(intent, 0);
} catch (Exception e) {    
    Uri marketUri = Uri.parse("market://details?id=com.google.zxing.client.android");
    Intent marketIntent = new Intent(Intent.ACTION_VIEW,marketUri);
    startActivity(marketIntent);
}

and in onActivityResult():

@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
    super.onActivityResult(requestCode, resultCode, data);
    if (requestCode == 0) {
        if (resultCode == RESULT_OK) {
            String contents = data.getStringExtra("SCAN_RESULT");
        }
        if(resultCode == RESULT_CANCELLED){
            //handle cancel
        }
    }
}

2016 update

The current recommendation is to use the Android Barcode API, which works locally (offline), without requiring a server roundtrip:

The Barcode API detects barcodes in real-time, on device, in any orientation. It can also detect multiple barcodes at once.

It reads the following barcode formats:

• 1D barcodes: EAN-13, EAN-8, UPC-A, UPC-E, Code-39, Code-93, Code-128, ITF, Codabar
• 2D barcodes: QR Code, Data Matrix, PDF-417, AZTEC

It automatically parses QR Codes, Data Matrix, PDF-417, and Aztec values, for the following supported formats:

• URL
• Contact information (VCARD, etc.)
• Calendar event
• Email
• Phone
• SMS
• ISBN
• WiFi
• Geo-location (latitude and longitude)
• AAMVA driver license/ID

Check out the codelab - Barcode Detection with the Mobile Vision API.

You can scan QR code easily with zxing add the following dependencies in your gradle

compile 'com.journeyapps:zxing-android-embedded:3.1.0@aar'
compile 'com.google.zxing:core:3.2.0'

Then in your Activity or on Fragment

   IntentIntegrator scanIntegrator = new IntentIntegrator(context);
                scanIntegrator.setPrompt("Scan");
                scanIntegrator.setBeepEnabled(true);
                //The following line if you want QR code
                scanIntegrator.setDesiredBarcodeFormats(IntentIntegrator.QR_CODE_TYPES);
                scanIntegrator.setCaptureActivity(CaptureActivityAnyOrientation.class);
                scanIntegrator.setOrientationLocked(true);
                scanIntegrator.setBarcodeImageEnabled(true);
                scanIntegrator.initiateScan();

And then capture the result in onActivityResult

   @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        super.onActivityResult(requestCode, resultCode, data);
        IntentResult scanningResult = IntentIntegrator.parseActivityResult(requestCode, resultCode, data);
        if (scanningResult != null) {
            if (scanningResult.getContents() != null) {
                scanContent = scanningResult.getContents().toString();
                scanFormat = scanningResult.getFormatName().toString();
            }

            Toast.makeText(this,scanContent+"   type:"+scanFormat,Toast.LENGTH_SHORT).show();

        }else{
            Toast.makeText(this,"Nothing scanned",Toast.LENGTH_SHORT).show();
        }
    }

Take a look at this sample project , hope it helps you .