如何在 Xamarin Forms 的默认应用程序中打开 PDF 或 TXT 文件

Question

I am going to open document using default app in Xamarin Forms. I tried already this approach but it doesn't work for me and I am not sure what is the reason.

Device.OpenUri(new Uri(FILE_PATH));

Please give me great solution if anyone knows how to handle it. Thanks.

Answer 1

You can use DependencyService to implement this from each platform. Firstly, create a interface from PCL for example like:

public interface IFileViewer
{
    void ShowPDFTXTFromLocal(string filename);
}

Then for Android platform, create a class to implement this interface:

[assembly: Xamarin.Forms.Dependency(typeof(FileViewer))]

namespace NameSpace.Droid
{
    public class FileViewer : IFileViewer
    {
        public void ShowPDFTXTFromLocal(string filename)
        {
            string dirPath = Xamarin.Forms.Forms.Context.GetExternalFilesDir(Android.OS.Environment.DirectoryDocuments).Path;
            var file = new Java.IO.File(dirPath, System.IO.Path.Combine(dirPath, filename));

            if (file.Exists())
            {
                Xamarin.Forms.Device.BeginInvokeOnMainThread(() =>
                {
                    var uri = Android.Net.Uri.FromFile(file);
                    Intent intent = new Intent(Intent.ActionView);
                    var mimetype = MimeTypeMap.Singleton.GetMimeTypeFromExtension(MimeTypeMap.GetFileExtensionFromUrl((string)uri).ToLower());
                    intent.SetDataAndType(uri, mimetype);
                    intent.SetFlags(ActivityFlags.ClearWhenTaskReset | ActivityFlags.NewTask);

                    try
                    {
                        Xamarin.Forms.Forms.Context.StartActivity(intent);
                    }
                    catch (Exception ex)
                    {
                        System.Diagnostics.Debug.WriteLine(ex.ToString());
                    }
                });
            }
            else
            {
                System.Diagnostics.Debug.WriteLine("file not found");
            }
        }
    }
}

This is a example only works for the files which be placed in GetExternalFilesDir(Android.OS.Environment.DirectoryDocuments) , if your files are in other place, you will need to modify the code.

Answer 2

I implemented below code and worked perfectly. I hope that this code will help others.

var PreviewController = UIDocumentInteractionController.FromUrl(NSUrl.FromFilename(filePath));
PreviewController.Delegate = new UIDocumentInteractionControllerDelegateClass(UIApplication.SharedApplication.KeyWindow.RootViewController);
Device.BeginInvokeOnMainThread(() =>
{
    PreviewController.PresentPreview(true);
});

public class UIDocumentInteractionControllerDelegateClass : UIDocumentInteractionControllerDelegate
{
    UIViewController ownerVC;

    public UIDocumentInteractionControllerDelegateClass(UIViewController vc)
    {
        ownerVC = vc;
    }

    public override UIViewController ViewControllerForPreview(UIDocumentInteractionController controller)
    {
        return ownerVC;
    }

    public override UIView ViewForPreview(UIDocumentInteractionController controller)
    {
        return ownerVC.View;
    }
}

Answer 3

2020 update: Xamarin now has a very simple solution for this using Xamarin.Essentials. You can use a single line of code to open a file in the default application using Launcher.OpenAsync:

await Launcher.OpenAsync(new OpenFileRequest { File = new ReadOnlyFile(uri) });

Here is some sample code I am using in my app to open PDF files in the default application:

private void BtnOpen_Clicked(object sender, EventArgs e)
{
    string filePathAndName = Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData), "test.pdf");
    OpenPdf(filePathAndName);
}

public async void OpenPdf(string uri)
{
    await Launcher.OpenAsync(new OpenFileRequest { File = new ReadOnlyFile(uri) });
}

This will work on any platform with no custom renderers needed (as long as you have Xamarin.Essentials added to each project). Here is a link to the Microsoft documentation which provides some additional information.