Iphone 在ABPeoplePickerNavigationController中设置提示

我无法让此代码设置提示：

// Create a PeoplePicker
ABPeoplePickerNavigationController *objPeoplePicker = [[ABPeoplePickerNavigationController alloc] init];
[objPeoplePicker setPeoplePickerDelegate:self];

// Customize colors
objPeoplePicker.topViewController.navigationController.navigationBar.tintColor = [UIColor colorWithRed:0.294 green:0.278 blue:0.247 alpha:1.0];
objPeoplePicker.topViewController.searchDisplayController.searchBar.tintColor = [UIColor colorWithRed:0.294 green:0.278 blue:0.247 alpha:1.0];

// Only display phone numbers
NSArray *displayedItems = [NSArray arrayWithObjects:[NSNumber numberWithInt:kABPersonPhoneProperty], nil];
objPeoplePicker.displayedProperties = displayedItems;

// Add a prompt
objPeoplePicker.navigationBar.topItem.prompt = @"Choose a contact to...";

// Show the picker
[self presentModalViewController:objPeoplePicker animated:YES];

“添加提示”部分似乎没有设置提示。有什么想法吗？以下是输出的屏幕截图：

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这个问题的关键信息（不是很明显）是需要在行后设置提示：

[self presentModalViewController:objPeoplePicker animated:YES];

所以，如果你这样做，它会起作用：

[self presentModalViewController:objPeoplePicker animated:YES];
objPeoplePicker.navigationBar.topItem.prompt = @"Choose a contact to...";