在iPhone上点击背景图片

Question

I want to do something when the background was tapped on iPhone.

How to enable the background tapping?

I put a sample background on my app using this code.

- void viewDidLoad{

     [super viewDidLoad];
     UIGraphicsBeginImageContext(self.view.frame.size);
     [[UIImage imageNamed:@"backgroundimage.jpeg"] drawInRect:self.view.bounds];
     UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
     UIGraphicsEndImageContext();
}

How to do background tapping?

For example I want to click the background and a message will pop up " Background was tapped!" .

Do i need IBAction for that?

Need help.

Answer 1

What you could do is use an IBAction, which would be a lot simpler code.

In your header file of your view controller, do this:

- (IBAction)backgroundTap:(id)sender;

In your implementation file of your view controller, do this:

- (IBAction)backgroundTap:(id)sender
{

}

In the storyboard, assuming that you have linked up view controller GUI with your view controller class, click on the background of the view controller GUI and then show the Identity Inspector in the Utilities view, which should show up on the right. Then, under custom class, which should currently be blank, type in UIControl. Now go to the connections inspector and link at Touch Down to the background, selecting backgroundTap. Now, anything inside the backgroundTap method will be what will happen when you select the background.

Answer 2

UIButton is the simplest way.

- (void)backgroundButtonClicked:(id)sender
{
    UIAlertView *alertView = [[UIAlertView alloc] initWithTitle:nil message:@"Background was tapped!" delegate:nil cancelButtonTitle:@"OK" otherButtonTitles:nil];
    [alertView show];
    [alertView release];
}

- (void)viewDidLoad
{
    [super viewDidLoad];
    /*
     * Your other code here
     */
    UIButton *backgroundButton = [UIButton buttonWithType:UIButtonTypeCustom];
    backgroundButton.backgroundColor = [UIColor clearColor];
    backgroundButton.frame = self.view.bounds;
    [backgroundButton addTarget:self action:@selector(backgroundButtonClicked:) forControlEvents:UIControlEventTouchUpInside];
    [self.view addSubview:backgroundButton];
    [self.view sendSubviewToBack:backgroundButton];
}

BTW, there is no need to draw a background image because [UIImage imageNamed:@"imagename"] returns an image. If you want to present it, try putting the code in your -viewDidLoad :

UIImageView *imageView = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"backgroundimage.jpeg"]];
imageView.frame = self.view.bounds;
[self.view insertSubview:imageView belowSubview:backgroundButton];
[imageView release];

Edit:

Thanks to @AlexMDC for reminding me of UITapGestureRecognizer . Here is the UITapGestureRecognizer version:

- (void)tapped:(UITapGestureRecognizer *)g
{
    UIAlertView *alertView = [[UIAlertView alloc] initWithTitle:nil message:@"Background was tapped!" delegate:nil cancelButtonTitle:@"OK" otherButtonTitles:nil];
    [alertView show];
    [alertView release];
}

- (void)viewDidLoad
{
    [super viewDidLoad];
    /*
     * Your other code here
     */
    UITapGestureRecognizer*tap = [[UITapGestureRecognizer alloc] init];
    [tap addTarget:self action:@selector(tapped:)];
    [self.view addGestureRecognizer:tap];
    [tap release];
}

Both versions meet the requirements. Admittedly, UITapGestureRecognizer is more powerful and more flexible. However, I'd prefer UIButton to do the trick this time. It's more lightweight than gesture recognizer. I needn't care about the state of the gesture recognizer, whether touch events have been blocked by it or how to implement the UIGestureRecognizerDelegate .
It's more likely the case that we want to add some other UIView or subclasses of UIView on the controller's view. At this point, the UITapGestureRecognizer version need to exclude all the non-background areas in – gestureRecognizerShouldBegin: delegate method.
If detecting double tap is the new requirement, it is still not too late to refactor the UIButton to the UITapGestureRecognizer .