问题
I have a UIPickerView that gets faded out to 20% alpha when not in use. I want the user to be able to touch the picker and have it fade back in.
I can get it to work if I put a touchesBegan method on the main View, but this only works when the user touches the View. I tried sub-classing UIPickerView and having a touchesBegan in there, but it didn't work.
I'm guessing it's something to do with the Responder chain, but can't seem to work it out.
回答1:
I've been searching for a solution to this problem for over a week. I'm answering you even if you're question is over a year old hoping this helps others.
Sorry if my language is not very technical, but I'm pretty new to Objective-C and iPhone development.
Subclassing UIpickerView is the right way to do it. But you've to override the - (UIView *)hitTest:(CGPoint)point withEvent:(UIEvent *)event method. This is the method called whenever you touch the screen and it returns the view that will react to the touch. In other words the view whose touchesBegan:withEvent: method will be called.
The UIPickerView has 9 subviews! In the UIPickerView class implementation - (UIView *)hitTest:(CGPoint)point withEvent:(UIEvent *)event won't return self (this means the touchesBegan:withEvent: you write in the subclass won't be called) but will return a subview, exactly the view at index 4 (an undocumented subclass called UIPickerTable).
The trick is to make the - (UIView *)hitTest:(CGPoint)point withEvent:(UIEvent *)event method to return self so you have control over the touchesBegan:withEvent:, touchesMoved:withEvent: and touchesEnded:withEvent: methods.
In these methods, in order to keep the standard functionalities of the UIPickerView, you MUST remember to call them again but on the UIPickerTable subview.
I hope this makes sense. I can't write code now, as soon as I'm at home I will edit this answer and add some code.
回答2:
Here is some code that does what you want:
@interface TouchDetectionView : UIPickerView {
}
- (UIView *)getNextResponderView:(NSSet *)touches withEvent:(UIEvent *)event;
@end
@implementation TouchDetectionView
- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
UIView * hitTestView = [self getNextResponderView:touches withEvent:event];
[hitTestView touchesBegan:touches withEvent:event];
}
- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
{
UIView * hitTestView = [self getNextResponderView:touches withEvent:event];
[hitTestView touchesMoved:touches withEvent:event];
}
- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event
{
UIView * hitTestView = [self getNextResponderView:touches withEvent:event];
[hitTestView touchesEnded:touches withEvent:event];
}
- (void)touchesCancelled:(NSSet *)touches withEvent:(UIEvent *)event
{
UIView * hitTestView = [self getNextResponderView:touches withEvent:event];
[hitTestView touchesCancelled:touches withEvent:event];
}
- (UIView *)hitTest:(CGPoint)point withEvent:(UIEvent *)event
{
return self;
}
- (UIView *)getNextResponderView:(NSSet *)touches withEvent:(UIEvent *)event
{
UITouch * touch = [touches anyObject];
CGPoint point = [touch locationInView:self];
UIView * hitTestView = [super hitTest:point withEvent:event];
return ( hitTestView == self ) ? nil : hitTestView;
}
回答3:
Both of the above answers were very helpful, but I have a UIPickerView nested within a UIScrollView. I'm also doing continual rendering elsewhere on-screen while the GUI is present. The problem is that the UIPickerView doesn't update fully when: a non-selected row is tapped, the picker is moved so that two rows straddle the selection area, or a row is dragged but the finger slides outside of the UIPickerView. Then it's not until the UIScrollView is moved that the picker instantly updates. This result is ugly.
The problem's cause: my continual rendering was keeping the UIPickerView's animation from getting the CPU cycles it needed to finish, hence to show the correct, current selection. My solution --which works-- was this: in the UIPickerView's touchesEnded:withEvent:, execute something to pause my rendering for a short while. Here's the code:
#import "SubUIPickerView.h"
@implementation SubUIPickerView
- (void) touchesBegan:(NSSet*)touches withEvent:(UIEvent*)event
{
[pickerTable touchesBegan:touches withEvent:event];
}
- (void) touchesMoved:(NSSet*)touches withEvent:(UIEvent*)event
{
[pickerTable touchesMoved:touches withEvent:event];
}
- (void) touchesEnded:(NSSet*)touches withEvent:(UIEvent*)event
{
[singleton set_secondsPauseRendering:0.5f]; // <-- my code to pause rendering
[pickerTable touchesEnded:touches withEvent:event];
}
- (void) touchesCancelled:(NSSet*)touches withEvent:(UIEvent*)event
{
[pickerTable touchesCancelled:touches withEvent:event];
}
- (UIView*) hitTest:(CGPoint)point withEvent:(UIEvent*)event
{
if (CGRectContainsPoint(self.bounds, point))
{
if (pickerTable == nil)
{
int nSubviews = self.subviews.count;
for (int i = 0; i < nSubviews; ++i)
{
UIView* view = (UIView*) [self.subviews objectAtIndex:i];
if ([view isKindOfClass:NSClassFromString(@"UIPickerTable")])
{
pickerTable = (UIPickerTable*) view;
break;
}
}
}
return self; // i.e., *WE* will respond to the hit and pass it to UIPickerTable, above.
}
return [super hitTest:point withEvent:event];
}
@end
and then the header, SubUIPickerView.h:
@class UIPickerTable;
@interface SubUIPickerView : UIPickerView
{
UIPickerTable* pickerTable;
}
@end
Like I said, this works. Rendering pauses for an additional 1/2 second (it already pauses when you slide the UIScrollView) allowing the UIPickerView animation to finish. Using NSClassFromString() means you're not using any undocumented APIs. Messing with the Responder chain was not necessary. Thanks to checcco and Tylerc230 for helping me come up with my own solution!
回答4:
Set canCancelContentTouches and delaysContentTouches of parent view to NO, that worked for me
来源：https://stackoverflow.com/questions/567805/responding-to-touchesbegan-in-uipickerview-instead-of-uiview