点击时，UIButton图像不会改变

Question

I need to have an image button change to a different image when I tap it. Simple enough, and there are samples out there, but they don't work for me. This is what I tried following the examples:

UIButton *button = [UIButton buttonWithType:UIButtonTypeRoundedRect];
button.frame = CGRectMake(20, 270, 200, 40.0);
[button setImage:[UIImage imageNamed:@"butterfly3.png"] forState:UIControlStateNormal];
[button setImage:[UIImage imageNamed:@"clicked.png"] forState:UIControlStateSelected | UIControlStateHighlighted];
[button addTarget:self action:@selector(buttonPressed) forControlEvents:UIControlEventTouchDown];
[button setTitle:@"Submit" forState:UIControlStateNormal];
[scrollView button];

Now, I notice that my button is set to perform its action on UIControlEventTouchDown so I added it to the "clicked" control states like this:

[button setImage:[UIImage imageNamed:@"clicked.png"] forState:UIControlStateSelected | UIControlStateHighlighted | UIControlEventTouchDown];

but the image still stays the same. What am I missing?

Answer 1

The issue was that my buttonPressed method did a long(ish) query on the main thread and for some reason the highlighting of the button doesn't work in such a case.

When I moved the query to a separate thread the highlight went back on.

For the sake of completion I'll bring the code here. Initially I was fetching objects through Parse.com API like this:

[myQuery findObjects]

This above does the query on the main thread and blocks everything else.

Then I changed it to fetching in a separate thread like this:

[myQuery findObjectsInBackgroundWithBlock:^(NSArray *objects, NSError *error) {
    if(!error) {
            // whatever is needed to be done
        }
    } else {
        NSLog(@"Error while fetching objects %@", error.description);
    }
}];

Answer 2

Just change your code by this, and everything will work!

[button setImage:[UIImage imageNamed:@"clicked.png"] forState:UIControlStateHighlighted];
[button setImage:[UIImage imageNamed:@"clicked.png"] forState:UIControlStateSelected];

Answer 3

Inside buttonPressed method set yourButton.selected = YES; Also set image as Miroslav mentioned.

Answer 4

It appears that you are putting an event mask UIControlEventTouchDown that is being interpreted as a state mask in this line:

[button setImage:[UIImage imageNamed:@"clicked.png"] forState:UIControlStateSelected | UIControlStateHighlighted | UIControlEventTouchDown];

In fact I think you may not need this line at all, as you've already set the appropriate images. Try removing UIControlEventTouchDown from this line or comment out the whole line.