SteamTools/System.Common.ClientLib/Application/Services/Implementation/PermissionsImpl.cs

using System.Threading.Tasks;
using Xamarin.Essentials;

namespace System.Application.Services.Implementation
{
    /// <inheritdoc cref="IPermissions"/>
    public class PermissionsImpl : IPermissions
    {
        /// <summary>
        /// 权限被拒绝，可提示用户在“设置”中启用，通常应有不再提示的选项
        /// </summary>
        /// <param name="permission"></param>
        protected virtual void PromptUserGoToSettings(IPermissions.IPermission permission)
        {
            // 可由平台重写此函数实现，通常为显示一个UI上的弹窗，上有复选框不再显示
        }

        /// <summary>
        /// 提示用户需要权限的其他信息
        /// </summary>
        /// <param name="permission"></param>
        protected virtual void ShowRationale(IPermissions.IPermission permission)
        {
            // 可由平台重写此函数实现，通常为显示一个吐司消息，因调用此函数后会立即开始重新申请权限
        }

        public async Task<PermissionStatus> CheckAndRequestAsync(IPermissions.IPermission permission)
        {
            // https://docs.microsoft.com/zh-cn/xamarin/essentials/permissions?context=xamarin%2Fandroid&tabs=android#general-usage
            var status = await permission.CheckStatusAsync();

            if (status == PermissionStatus.Granted)
                return status;

            if (status == PermissionStatus.Denied && DeviceInfo.Platform == DevicePlatform.iOS)
            {
                // Prompt the user to turn on in settings
                // 提示用户在“设置”中启用
                // On iOS once a permission has been denied it may not be requested again from the application
                // 在iOS上，一旦权限被拒绝，就不能再次从应用程序请求权限
                PromptUserGoToSettings(permission);
                return status;
            }

            if (permission.ShouldShowRationale())
            {
                // Prompt the user with additional information as to why the permission is needed
                // 提示用户需要权限的其他信息
                ShowRationale(permission);
            }

            status = await permission.RequestAsync();

            if (status == PermissionStatus.Denied)
            {
                PromptUserGoToSettings(permission);
            }

            return status;
        }
    }
}