自定义UIToolbar的不同外观作为iOS6设备上的inputAccessoryView＆amp;模拟器

Question

我正在尝试在我的iOS6通用应用程序中使用透明的UIToolbar作为UITextField的inputAccessoryView。

在iOS6 iphone上运行时，工具栏显示为透明但有顶部边框。这只发生在iOS6 iphone上。不在iOS6 ipad设备上，不在iOS6 ipad模拟器上，甚至不在iOS6 iPhone模拟器上。以下是设备和模拟器的截图...

这是我的代码......

// Transparent Toolbar.m

@implementation TransparentToolbar
- (void)drawRect:(CGRect)rect
{
    CGContextRef context = UIGraphicsGetCurrentContext();
    [[UIColor clearColor] setFill];
    CGContextFillRect(context, self.bounds);
}
@end

// ViewController.m

#import "ViewController.h"
#import "TransparentToolbar.h"

@interface ViewController () {
    TransparentToolbar *_accessoryView;
}
@end

@implementation ViewController
@synthesize textField;
- (TransparentToolbar *)_accessoryView
{
    if (!_accessoryView) {
        _accessoryView = [[TransparentToolbar alloc] init];
        [_accessoryView sizeToFit];
        [_accessoryView setTranslucent:YES];

        UIBarButtonItem *flexButton = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemFlexibleSpace target:self action:nil];

        UIButton *resignKeyboardButton = [UIButton buttonWithType:UIButtonTypeInfoDark];
        [resignKeyboardButton setFrame:CGRectMake(0, 0, 44, 44)];
        [resignKeyboardButton setTitle:@"DONE" forState:UIControlStateNormal];
        [resignKeyboardButton addTarget:self action:@selector(didTapResignKeyboardButton:) forControlEvents:UIControlEventTouchUpInside];

        UIBarButtonItem *resignKeyboardBarButton =[[UIBarButtonItem alloc] initWithCustomView:resignKeyboardButton];

        NSArray *itemsArray = [NSArray arrayWithObjects:flexButton, resignKeyboardBarButton, nil];
        [_accessoryView setItems:itemsArray];
    }

    return _accessoryView;
}

- (void)viewDidLoad
{
    [super viewDidLoad];
    [textField setInputAccessoryView:[self _accessoryView]];
}

- (void)didTapResignKeyboardButton:(UIBarButtonItem *)aButtonItem
{
    [textField resignFirstResponder];
}
@end

这里可能出现什么问题？