如何在xamarin表单中自定义ZXingDefaultOverlay

<zxing:ZXingScannerView x:Name="scannerView" OnScanResult="OnScanResult" />

var overlay = new ZXingDefaultOverlay
{
    TopText = "将二维码放置在框内，即可自动扫描",
    BottomText = "请稍等...",
    ShowFlashButton = true
};

var scannerView = new ZXingScannerView
{
    HorizontalOptions = LayoutOptions.FillAndExpand,
    VerticalOptions = LayoutOptions.FillAndExpand,
    AutomationId = "scannerView"
};

scannerView.Options = new ZXing.Mobile.MobileBarcodeScanningOptions
{
    PossibleFormats = new List<ZXing.BarcodeFormat>
    {
        ZXing.BarcodeFormat.QR_CODE
    }
};

scannerView.OnScanResult += (result) =>
{
    // 处理扫描结果
    scannerView.IsAnalyzing = false;

    Device.BeginInvokeOnMainThread(async () =>
    {
        await DisplayAlert("扫描结果", result.Text, "确定");
        scannerView.IsAnalyzing = true;
    });
};

scannerView.Options.DelayBetweenContinuousScans = 3000;
scannerView.Options.ContinuousScanning = true;
scannerView.Options.TryHarder = true;

Content = new StackLayout
{
    Children =
    {
        scannerView,
        overlay
    }
};