一、从系统“文件”APP选择文件上传

#import "ViewController.h"

@interface ViewController () <UIDocumentPickerDelegate>

@property (nonatomic, strong) UIDocumentPickerViewController *documentPickerVC;

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
}

- (IBAction)tapSelectFileAction:(id)sender {
    dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(0.35 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
        [self presentViewController:self.documentPickerVC animated:YES completion:nil];
    });
}

/**
 初始化 UIDocumentPickerViewController
 
 @param allowedUTIs 支持的文件类型数组
 "public.content",
 "public.text",
 "public.source-code",
 "public.image",
 "public.audiovisual-content",
 "com.adobe.pdf",
 "com.apple.keynote.key",
 "com.microsoft.word.doc",
 "com.microsoft.excel.xls",
 "com.microsoft.powerpoint.ppt"
 @param mode 支持的共享模式
 */
- (UIDocumentPickerViewController *)documentPickerVC {
    if (!_documentPickerVC) {
        NSArray *types = @[@"public.content",@"public.text"];
        self.documentPickerVC = [[UIDocumentPickerViewController alloc] initWithDocumentTypes:types inMode:UIDocumentPickerModeOpen];
        // 设置代理
        _documentPickerVC.delegate = self;
        // 设置模态弹出方式
        _documentPickerVC.modalPresentationStyle = UIModalPresentationFormSheet;
    }
    return _documentPickerVC;
}

#pragma mark - UIDocumentPickerDelegate

- (void)documentPicker:(UIDocumentPickerViewController *)controller didPickDocumentsAtURLs:(NSArray<NSURL *> *)urls {
    // 获取授权
    BOOL fileUrlAuthozied = [urls.firstObject startAccessingSecurityScopedResource];
    if (fileUrlAuthozied) {
        // 通过文件协调工具来得到新的文件地址，以此得到文件保护功能
        NSFileCoordinator *fileCoordinator = [[NSFileCoordinator alloc] init];
        NSError *error;
        
        [fileCoordinator coordinateReadingItemAtURL:urls.firstObject options:0 error:&error byAccessor:^(NSURL *newURL) {
            // 读取文件
            NSString *fileName = [newURL lastPathComponent];
            NSError *error = nil;
            NSData *fileData = [NSData dataWithContentsOfURL:newURL options:NSDataReadingMappedIfSafe error:&error];
            if (error) {
                // 读取出错
            } else {
                // 上传
                NSLog(@"fileName : %@", fileName);
                // [self uploadingWithFileData:fileData fileName:fileName fileURL:newURL];
            }
            [self dismissViewControllerAnimated:YES completion:NULL];
        }];
        [urls.firstObject stopAccessingSecurityScopedResource];
    } else {
        // 授权失败
    }
}

@end

二、从开发APP中保存文件到系统“文件”APP

#pragma mark - 下载文件
/// http://jadinec-test.oss-accelerate.aliyuncs.com/excelFile/a5f23e130d5e4dd7adda942c45207927.pdf
- (void)downLoadWithFilePath:(NSString *)filePath {
    float version = [[[UIDevice currentDevice] systemVersion] floatValue];
    if (version >= 11) {
        
    } else {
        [MBProgressHUD showError:@"下载文件要求手机系统版本在11.0以上"];
        return;
    }
    /**
    /// 保存网络文件到沙盒一
    NSURLRequest *req = [[NSURLRequest alloc] initWithURL:[NSURL URLWithString:filePath]];
    NSData *fileData = [NSURLConnection sendSynchronousRequest:req returningResponse:nil error:nil];
    NSString *temp = NSTemporaryDirectory();
    NSFileManager *fm = [NSFileManager defaultManager];
    NSString *fullPath = [self getNativeFilePath:[filePath componentsSeparatedByString:@"/"].lastObject];
    BOOL downResult = [fm createFileAtPath:fullPath contents:fileData attributes:nil];
    */
    /// 保存网络文件到沙盒二
    NSData *fileData = [NSData dataWithContentsOfURL:[NSURL URLWithString:filePath]];
    NSString *fullPath = [self getNativeFilePath:[filePath componentsSeparatedByString:@"/"].lastObject];
    BOOL downResult = [fileData writeToFile:fullPath atomically:YES];
    
    if (downResult) {
        UIDocumentPickerViewController *documentPickerVC = [[UIDocumentPickerViewController alloc] initWithURL:[NSURL fileURLWithPath:fullPath] inMode:UIDocumentPickerModeExportToService];
        // 设置代理
        documentPickerVC.delegate = self;
        // 设置模态弹出方式
        documentPickerVC.modalPresentationStyle = UIModalPresentationFormSheet;
        [self.navigationController presentViewController:documentPickerVC animated:YES completion:nil];
    }
}

// 获得文件沙盒地址
- (NSString *)getNativeFilePath:(NSString *)fileName {
    NSString *path = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) lastObject];
    NSString *munu = [NSString stringWithFormat:@"%@/%@",@"downLoad",fileName];
    NSString *filePath = [path stringByAppendingPathComponent:munu];
    // 判断是否存在,不存在则创建
    NSFileManager *fileManager = [NSFileManager defaultManager];
    // fileExistsAtPath 判断一个文件或目录是否有效，isDirectory判断是否一个目录
    BOOL isDir = NO;
    NSMutableArray *theArr = [[filePath componentsSeparatedByString:@"/"] mutableCopy];
    [theArr removeLastObject];
    NSString *thePath = [theArr componentsJoinedByString:@"/"];
    BOOL existed = [fileManager fileExistsAtPath:thePath isDirectory:&isDir];
    if ( !(isDir == YES && existed == YES) ) { // 如果文件夹不存在
        [fileManager createDirectoryAtPath:thePath withIntermediateDirectories:YES attributes:nil error:nil];
    }
    return filePath;
}

#pragma mark - UIDocumentPickerDelegate
 
- (void)documentPicker:(UIDocumentPickerViewController *)controller didPickDocumentsAtURLs:(NSArray<NSURL *> *)urls {
    // 获取授权
    BOOL fileUrlAuthozied = [urls.firstObject startAccessingSecurityScopedResource];
    if (fileUrlAuthozied) {
        // 通过文件协调工具来得到新的文件地址，以此得到文件保护功能
        NSFileCoordinator *fileCoordinator = [[NSFileCoordinator alloc] init];
        NSError *error;
        
        [fileCoordinator coordinateReadingItemAtURL:urls.firstObject options:0 error:&error byAccessor:^(NSURL *newURL) {
            // 读取文件
            NSString *fileName = [newURL lastPathComponent];
            NSError *error = nil;
            //NSData *fileData = [NSData dataWithContentsOfURL:newURL options:NSDataReadingMappedIfSafe error:&error];
            if (error) {
                // 读取出错
            } else {
                // 上传
                NSLog(@"fileName : %@", fileName);
            }
        }];
        [urls.firstObject stopAccessingSecurityScopedResource];
    } else {
        // 授权失败
    }
}

TO:

UIDocumentPickerViewController
https://blog.csdn.net/u014084081/article/details/94563298
UIDocumentPickerViewController.h
https://www.jianshu.com/p/75eb512811d9
iOS让APP中的文件在系统的File应用显示
https://www.jianshu.com/p/0d0f2be26cec
UIDocumentPickerViewController和UIDocumentInteractionController
https://www.cnblogs.com/zhouhui231/p/12183125.html