Mobile: Long press on images or other attachments to share them (#3367)

ReactNativeClient/lib/components/BackButtonDialogBox.ts

@@ -0,0 +1,24 @@
+const { BackButtonService } = require('lib/services/back-button.js');
+const DialogBox = require('react-native-dialogbox').default;
+
+export default class BackButtonDialogBox extends DialogBox {
+	constructor() {
+		super();
+
+		this.backHandler_ = () => {
+			if (this.state.isVisible) {
+				this.close();
+				return true;
+			}
+			return false;
+		};
+	}
+
+	componentDidMount() {
+		BackButtonService.addHandler(this.backHandler_);
+	}
+
+	componentWillUnmount() {
+		BackButtonService.removeHandler(this.backHandler_);
+	}
+}