UISlider won't work when it becomes a subview

问题:

When I add my slider as subview of any view besides self.view it does not work (doesn't slide) but it works fine when it is a subview of self.view. You can see it on the other views besides self.view but it doesn't work.

Here is my code:

alphaSlider = [[UISlider alloc] initWithFrame:CGRectMake(0, 0, 90, 10)];
    [alphaSlider setMinimumValue:0.01];
    [alphaSlider setMaximumValue:1];
    [alphaSlider setValue:0.5];
    [alphaSlider setUserInteractionEnabled:YES];
    [alphaSlider addTarget:self action:@selector(alphaSliderDidChange:) forControlEvents:UIControlEventValueChanged];
    alphaSlider.continuous = YES;
[submenu addSubview:alphaSlider];

Any way to fix this?

回答1:

It may be that submenu is not enabled for user interaction.

[submenu setUserInteractionEnabled:YES];

Another possibility is that the slider's frame is outside of submenu.frame

Since the clipsToBounds property of UIViews is by default NO, the slider would not be clipped despite being outside of submenu's frame. This means that submenu's frame doesn't cover the slider, and there's no way to pass touch events from submenu to submenu's slider. Set the background color of submenu and confirm that the slider is positioned entirely in submenu's frame.

[submenu setBackgroundColor:[UIColor blueColor]];

Submenu's frame might be something like (0, 0, 0, 0).

Include

NSLog(@"%f, %f, %f, %f", submenu.frame.origin.x, submenu.frame.origin.y, submenu.frame.size.width, submenu.frame.size.height);

You could also do

[submenu setClipsToBounds:YES];

and if the slider disappears, then submenu's frame is bad.

回答2:

Check that the frame height of the slider is not too small to allow interaction. 10 pt is probably too small.

Starting in iOS 8, my sliders also stopped working.

In the past, the frame height of UIViews like UISlider, UISwitch, and UIPickerView has been fixed to some pre-defined value. You could set the frame height, but it would be ignored. Instead of trying to remember, "What is the height of a UISlider in Landscape on the iPad/iPhone?", I had been setting the height to 0 and let the OS assign the default value.

David Braun's answer led me to realize that my UISlider frames had height 0 which disabled user interaction.

回答3:

I had a similar problem, where the slider did not have the horizontal line, just the white button and did not respond at all. Based on the above I realized, that my sliders were wider than my safe area. Set some constraints on the 2 sides, and now it works just fine.