How to scan a barcode from another Android application via Intents

How to scan a barcode from another Android application via Intents
透過其他的應用程式，使用其內部所提供的功能
    public Button.OnClickListener mScan = new Button.OnClickListener() {
        public void onClick(View v) {
            Intent intent = new Intent("com.google.zxing.client.android.SCAN");
            intent.setPackage("com.google.zxing.client.android");
            // "SCAN_MODE" for all unknow code
            intent.putExtra("SCAN_MODE", "QR_CODE_MODE");
            // use this method, can get the response by "onActivityResult( )"
            startActivityForResult(intent, 0);
        }
    };
    // receive the result    public void onActivityResult(int requestCode, int resultCode, Intent intent) {
        if (requestCode == 0) {  // this line maybe can marked
            if (resultCode == RESULT_OK) {  // -1
                String contents = intent.getStringExtra("SCAN_RESULT");
                String format = intent.getStringExtra("SCAN_RESULT_FORMAT");
                // Handle successful scan
            } else if (resultCode == RESULT_CANCELED) {  // 0
                // Handle cancel
            }
        }
    }