第一次在 xamarin 表单中使用 webview 保存空白页

Question

我有 local html file 我想将 html 保存到本地路径中加载的 Webview。 但第一次总是保存空数据。

 try 
        {
            htmltopdfs = html;
            var dir = new Java.IO.File(Android.OS.Environment.ExternalStorageDirectory.AbsolutePath + "/SVSTATIONERY/");
            var file = new Java.IO.File(dir + "/" + fileName + ".pdf");

            if (!dir.Exists())
                dir.Mkdirs();
            //else
            //    dir.Delete();

            int x = 0;
            while (file.Exists())
            {
                x++;
                file = new Java.IO.File(dir + "/" + fileName + "( " + x + " )" + ".pdf");
            }

            //if (webpage == null)
            var webpage = new Android.Webkit.WebView(MainActivity.context);

            int width = 2102;
            int height = 2970;

            webpage.Layout(0, 0, width, height);
            webpage.LoadDataWithBaseURL("", htmltopdfs, "text/html", "UTF-8", null);
            webpage.SetWebViewClient(new WebViewCallBack(file.ToString()));

            return file.ToString();
        }
        catch (Java.Lang.Exception e)
        {
            return e.Message;
        }

Onpagefinished event

 class WebViewCallBack : WebViewClient
{

    string fileNameWithPath = null;

    public WebViewCallBack(string path)
    {
        this.fileNameWithPath = path;
    }

    public override void OnPageFinished(Android.Webkit.WebView myWebview, string url)
    {
        PdfDocument document = new Android.Graphics.Pdf.PdfDocument();
        PdfDocument.Page page = document.StartPage(new PdfDocument.PageInfo.Builder(2102, 3500, 1).Create());

        myWebview.Draw(page.Canvas);
        document.FinishPage(page);
        Stream filestream = new MemoryStream();
        FileOutputStream fos = new Java.IO.FileOutputStream(fileNameWithPath, false);

        document.WriteTo(filestream);
        fos.Write(((MemoryStream)filestream).ToArray(), 0, (int)filestream.Length);
        fos.Close();
    }


}

创建后，但第一次，空白页面已创建到本地路径，然后创建多次后正常工作。

Answer 1

这是我关于将 webview（加载本地 html）打印为 PDF 的演示。

这里正在运行 GIF()。

我在 xamarin 表单中的布局，如以下代码。

   <StackLayout>
    <Button Text="save" Clicked="Button_Clicked"/>
    <Entry x:Name="MyEntry" Text="5"></Entry>
    <Label x:Name="MyLabel"></Label>
    <!-- Place new controls here -->
    <WebView x:Name="MywebView" HeightRequest="1000" Navigated="MywebView_Navigated"
    WidthRequest="1000"/>
</StackLayout>

在 Android 成就中，我使用了 MessagingCenter 和 webview 的自定义渲染器来实现。

[assembly: ExportRenderer(typeof(Xamarin.Forms.WebView), typeof(MyWebviewRender))]

命名空间 MyWebView.Droid { MyWebviewRender 类：WebViewRenderer { 上下文上下文； 公共 MyWebviewRender（上下文上下文）：基础（上下文）{ this.context = 上下文； }

    protected override void OnElementChanged(ElementChangedEventArgs<Xamarin.Forms.WebView> e)
    {
        base.OnElementChanged(e);

        MessagingCenter.Subscribe<string>(this, "pdf", (key) => {

            var printManager = (PrintManager)context.GetSystemService(Context.PrintService);
            var printAdapter = new MyPrintDocumentAdapter(context, Control);
            var printJob = printManager.Print("MyPrintJob", printAdapter, null);

        });


    }

}

MyPrintDocumentAdapter.cs

    public class MyPrintDocumentAdapter : PrintDocumentAdapter
{

    View view;
    Context context;
    PrintedPdfDocument document;
    float scale;

    public MyPrintDocumentAdapter(Context context, View view)
    {
        this.view = view;
        this.context = context;
    }

    public override void OnLayout(PrintAttributes oldAttributes, PrintAttributes newAttributes, CancellationSignal cancellationSignal, LayoutResultCallback callback, Bundle extras)
    {
        document = new PrintedPdfDocument(context, newAttributes);

        CalculateScale(newAttributes);

        //set the printed PDF attributes
        var printInfo = new PrintDocumentInfo
            .Builder("MyPrint.pdf")
            .SetContentType(PrintContentType.Document)
            .SetPageCount(10)
            .Build();

        callback.OnLayoutFinished(printInfo, true);
    }

    public override void OnWrite(PageRange[] pages, ParcelFileDescriptor destination, CancellationSignal cancellationSignal, WriteResultCallback callback)
    {
        PrintedPdfDocument.Page page = document.StartPage(0);

        page.Canvas.Scale(scale, scale);

        view.Draw(page.Canvas);

        document.FinishPage(page);

        WritePrintedPdfDoc(destination);

        document.Close();

        document.Dispose();

        callback.OnWriteFinished(pages);
    }

    void CalculateScale(PrintAttributes newAttributes)
    {
        int dpi = Math.Max(newAttributes.GetResolution().HorizontalDpi, newAttributes.GetResolution().VerticalDpi);

        int leftMargin = (int)(dpi * (float)newAttributes.MinMargins.LeftMils / 1000);
        int rightMargin = (int)(dpi * (float)newAttributes.MinMargins.RightMils / 1000);
        int topMargin = (int)(dpi * (float)newAttributes.MinMargins.TopMils / 1000);
        int bottomMargin = (int)(dpi * (float)newAttributes.MinMargins.BottomMils / 1000);

        int w = (int)(dpi * (float)newAttributes.GetMediaSize().WidthMils / 1000) - leftMargin - rightMargin;
        int h = (int)(dpi * (float)newAttributes.GetMediaSize().HeightMils / 1000) - topMargin - bottomMargin;

        scale = Math.Min((float)document.PageContentRect.Width() / w, (float)document.PageContentRect.Height() / h);
    }

    void WritePrintedPdfDoc(ParcelFileDescriptor destination)
    {
        var i=destination.FileDescriptor;
        var javaStream = new Java.IO.FileOutputStream(destination.FileDescriptor);
        var osi = new OutputStreamInvoker(javaStream);
        using (var mem = new MemoryStream())
        {
            document.WriteTo(mem);
            var bytes = mem.ToArray();
            osi.Write(bytes, 0, bytes.Length);
        }
    }

}

这是我的演示链接。 https://github.com/851265601/PrintLocalWebview2PDF