QLPreviewController自定义分享按钮功能

QLPreviewController是iOS 提供的文档预览功能。
查看文件类型如下：
A QLPreviewController can display previews for the following items:

iWork documents
Microsoft Office documents (Office ‘97 and newer)
Rich Text Format (RTF) documents
PDF files
Images
Text files whose uniform type identifier (UTI) conforms to the public<wbr>.text type (see Uniform Type Identifiers Reference)
Comma-separated value (csv) files
3D models in USDZ format (with both standalone and AR views for viewing the model)

如果在navigationController中显示，可以自定义navigation bar上的按钮。
但是当你指定rightBarButtonItem时，原来右上角的分享按钮会自动显示到左下角，并不是隐藏。

如何实现share按钮的自定义功能？

创建QLPreviewController子类
重写- (void)viewWillAppear:(BOOL)animated指定share按钮的响应事件。

- (void)viewWillAppear:(BOOL)animated{
    [super viewWillAppear:animated];
    UIBarButtonItem *shareBtnItem = self.navigationItem.rightBarButtonItem;
    if (shareBtnItem) {
        [shareBtnItem setAction:@selector(showActivityController)];
    }
}

实现showActivityController方法。

- (void)showActivityController{
    NSURL *previewItemURL = self.currentPreviewItem.previewItemURL;
    NSArray *items = @[previewItemURL];
    UIActivityViewController *vc = [[UIActivityViewController alloc] initWithActivityItems:items applicationActivities:@[]];
    vc.completionWithItemsHandler = ^(UIActivityType  _Nullable activityType, BOOL completed, NSArray * _Nullable returnedItems, NSError * _Nullable activityError) {};
    [self presentViewController:vc animated:YES completion:NULL];
}

源码：https://github.com/bianfu/BFUIKit