Essentials/Xamarin.Essentials/FilePicker/FilePicker.android.cs

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Threading.Tasks;
using Android.Content;

namespace Xamarin.Essentials
{
    public static partial class FilePicker
    {
        static async Task<IEnumerable<FileResult>> PlatformPickAsync(PickOptions options, bool allowMultiple = false)
        {
            // Essentials supports >= API 19 where this action is available
            var action = Intent.ActionOpenDocument;

            var intent = new Intent(action);
            intent.SetType(FileSystem.MimeTypes.All);
            intent.PutExtra(Intent.ExtraAllowMultiple, allowMultiple);

            var allowedTypes = options?.FileTypes?.Value?.ToArray();
            if (allowedTypes?.Length > 0)
                intent.PutExtra(Intent.ExtraMimeTypes, allowedTypes);

            var pickerIntent = Intent.CreateChooser(intent, options?.PickerTitle ?? "Select file");

            try
            {
                var resultList = new List<FileResult>();
                void OnResult(Intent intent)
                {
                    // The uri returned is only temporary and only lives as long as the Activity that requested it,
                    // so this means that it will always be cleaned up by the time we need it because we are using
                    // an intermediate activity.

                    if (intent.ClipData == null)
                    {
                        var path = FileSystem.EnsurePhysicalPath(intent.Data);
                        resultList.Add(new FileResult(path));
                    }
                    else
                    {
                        for (var i = 0; i < intent.ClipData.ItemCount; i++)
                        {
                            var uri = intent.ClipData.GetItemAt(i).Uri;
                            var path = FileSystem.EnsurePhysicalPath(uri);
                            resultList.Add(new FileResult(path));
                        }
                    }
                }

                await IntermediateActivity.StartAsync(pickerIntent, Platform.requestCodeFilePicker, onResult: OnResult);

                return resultList;
            }
            catch (OperationCanceledException)
            {
                return null;
            }
        }
    }

    public partial class FilePickerFileType
    {
        static FilePickerFileType PlatformImageFileType() =>
            new FilePickerFileType(new Dictionary<DevicePlatform, IEnumerable<string>>
            {
                { DevicePlatform.Android, new[] { FileSystem.MimeTypes.ImagePng, FileSystem.MimeTypes.ImageJpg } }
            });

        static FilePickerFileType PlatformPngFileType() =>
            new FilePickerFileType(new Dictionary<DevicePlatform, IEnumerable<string>>
            {
                { DevicePlatform.Android, new[] { FileSystem.MimeTypes.ImagePng } }
            });

        static FilePickerFileType PlatformJpegFileType() =>
            new FilePickerFileType(new Dictionary<DevicePlatform, IEnumerable<string>>
            {
                { DevicePlatform.Android, new[] { FileSystem.MimeTypes.ImageJpg } }
            });

        static FilePickerFileType PlatformVideoFileType() =>
            new FilePickerFileType(new Dictionary<DevicePlatform, IEnumerable<string>>
            {
                { DevicePlatform.Android, new[] { FileSystem.MimeTypes.VideoAll } }
            });

        static FilePickerFileType PlatformPdfFileType() =>
            new FilePickerFileType(new Dictionary<DevicePlatform, IEnumerable<string>>
            {
                { DevicePlatform.Android, new[] { FileSystem.MimeTypes.Pdf } }
            });
    }
}