iPhone iOS如何按需重绘UINavigationBar？

我有使用外观属性更改导航栏颜色的代码 . 我想立即看到导航栏颜色的变化 . 但是，我找不到正确的调用来重绘导航栏 . 当我按下模态导航控制器时，它的颜色会发生变化，从而覆盖了导航栏 .

这不起作用：

AppDelegate* appDelegate = ((AppDelegate*)[[UIApplication sharedApplication] delegate]);

    [appDelegate.window setNeedsDisplay];

我也试过要求导航控制器的各种实例重绘他们的视图，这些都不起作用 .

What's the correct way to ask the UINavigationBar to redraw itself on demand?

谢谢！

UPDATE: Here's the code that works!

- (UIColor *) colorOfPoint:(CGPoint)point
    {
        unsigned char pixel[4] = {0};
        CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
        CGContextRef context = CGBitmapContextCreate(pixel, 1, 1, 8, 4, colorSpace, kCGImageAlphaPremultipliedLast);

        CGContextTranslateCTM(context, -point.x, -point.y);

        [self.view.layer renderInContext:context];

        CGContextRelease(context);
        CGColorSpaceRelease(colorSpace);

        NSLog(@"pixel: %d %d %d %d", pixel[0], pixel[1], pixel[2], pixel[3]);
        float red = pixel[0]/255.0;
        float green = pixel[1]/255.0;
        float blue = pixel[2]/255.0;
        float alpha = pixel[3]/255.0;
        UIColor *color = [UIColor colorWithRed:red green:green blue:blue alpha:alpha];

        [[NSUserDefaults standardUserDefaults] setFloat:red forKey:@"navBarRed"];
        [[NSUserDefaults standardUserDefaults] setFloat:green forKey:@"navBarGreen"];
        [[NSUserDefaults standardUserDefaults] setFloat:blue forKey:@"navBarBlue"];    
        [[NSUserDefaults standardUserDefaults] setFloat:alpha forKey:@"navBarAlpha"];



        return color;
    }





  - (IBAction)handleTapFrom:(id)sender {

        if([sender isKindOfClass:[UITapGestureRecognizer class]])
        {


            CGPoint location = [tapGestureRecognizer locationInView:self.view];

            //remember color preferences
         UIColor* navbarColor =  [self colorOfPoint:location];
            selectColorView.center = location;

            //UPDATE THE NAVBAR COLOR CODE HERE

    //this does not update immediately 
        float navBarRed = [[NSUserDefaults standardUserDefaults] floatForKey:@"navBarRed"];
        float navBarGreen = [[NSUserDefaults standardUserDefaults] floatForKey:@"navBarGreen"];    
        float navBarBlue = [[NSUserDefaults standardUserDefaults] floatForKey:@"navBarBlue"];
        float navBarAlpha = [[NSUserDefaults standardUserDefaults] floatForKey:@"navBarAlpha"];

       UIColor* navBarColor =  [UIColor colorWithRed:navBarRed green:navBarGreen blue:navBarBlue alpha:navBarAlpha];


//set the color of all newly created navbars
        [[UINavigationBar appearance] setTintColor:navBarColor];  
        [[UINavigationBar appearance] setBarStyle:UIBarStyleBlackTranslucent];
        [[UINavigationBar appearance] setAlpha:0.7];


        //update the toolbar appearance
        [[UIToolbar appearance] setTintColor:navBarColor];

//set the color of the current navbar, displaying immediate change
self.navigationController.navigationBar.tintColor = navbarColor;



        }



    }