无法在profilesParams ios中设置图片属性

Question

我无法在Facebook分享参数中设置图片属性。

每次我设置它时，它始终保持nil：

NSURL *url = [[NSURL alloc] initWithString:filePath];

    // Check if the Facebook app is installed and we can present the share dialog
    FBLinkShareParams *params = [[FBLinkShareParams alloc] init];
    params.link = [NSURL URLWithString:@"https://www.google.com"];
    params.name = @"Check if it works";
    params.caption = @"Yet to fix image capture and publishing it";
    params.picture = url;

那里有什么问题？