PickFiles 继承自： ClientAction

当控件被激活时，打开一个文件选择器对话框。

它等价于 pick_files，但由客户端在用户手势内部执行——而浏览器只有在此时才会打开 文件选择器。这也正是文件选择在 iOS 的 Web 应用中能够生效的原因。

与 pick_files() 不同，所选文件不会返回给调用方，而是 通过 on_result 事件送达。文件会一直与 file_picker 关联， 因此可以直接传给 upload。

Example: ```python picker = ft.FilePicker(on_result=handle_result) page.services.append(picker)

ft.Button("Upload", action=ft.PickFiles(picker, allow_multiple=True))
```

属性

名称	类型	默认值	说明
file_picker	FilePicker	action_	The FilePicker that opens the dialog and reports the result through its on_result event.
dialog_title	Optional[str]	action_None	The title of the dialog window.
initial_directory	Optional[str]	action_None	The initial directory where the dialog should open.
file_type	Optional[FilePickerFileType]	action_None	The file types allowed to be selected.
allowed_extensions	Optional[list[str]]	action_None	The allowed file extensions. Has effect only if file_type is CUSTOM.
allow_multiple	bool	action_False	Allow the selection of multiple files at once.
with_data	bool	action_False	Read selected file contents into bytes.
compression_quality	int	action_0	Image compression quality from 0 to 100. 0 disables compression.
cancel_upload_on_window_blur	bool	action_True	Web-only. Whether to treat browser window blur as a cancelled selection.
service_id	int	0	Internal id of the service that performs this action on the client.
method	str	''	Name of the service method invoked on the client.
args	dict[str, Any]	{}	Arguments passed to method.