show() {
      if (this.loading) {
        console.warn("Barcode scanning is already in progress."); // eslint-disable-line
        return;
      }
      if (!this._hasGetUserMedia()) {
        this.fireEvent("scan-error", {
          message: "getUserMedia() is not supported by your browser"
        });
        return;
      }
      this.loading = true;
      this._getUserPermission().then(() => this._showDialog()).catch(err => {
        this.fireEvent("scan-error", {
          message: err
        });
        this.loading = false;
      });
    }
Shows a dialog with the camera videostream. Starts a scan session.
@method
@name sap.ui.webc.fiori.BarcodeScannerDialog#show
@returns {void}
@public