Allowing user to select a UIPickerView row by tapping

问题

I'm trying to use a UIPicker View with a behavior somehow different of what's usually seen in iPhone code examples.

What I want to do is to allow users to scroll through the picker contents, but not to select a picker's row automatically (using the "didSelectRow" method from picker's delegate). Instead, I want to allow the user to touch the center row of the picker, which gets highlighted, and becomes the selection.

Is there any way to achieve this?

Thanks in advance.

回答1:

Add a gesture recogniser to the UIPickerView which triggers a target method in your object:

myGR = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(pickerTapped:)];
[myPicker addGestureRecognizer:myGR];

// target method

-(void)pickerTapped:(id)sender
{
// your code
}

回答2:

1. make a new UIControl

   • same position as the UIPickerView
   • [yourcontrol setBackGroundColor: [UIColor clearColor]];

2. make a method

- (IBAction) pickerControlTapped 
{
    [yourpicker selectRow: rand()% yourpickersize
              inComponent: 0
                 animated: YES];
}

.3. make a connection between 1 and 2

 
[yourcontrol addTarget: self 
                action: @selector(pickerControlTapped) 
      forControlEvents: UIControlEventTouchUpInsied];

回答3:

Building on Martin Linklater's answer to support tapping on the pickers other rows: Has some magic numbers but works for me.

- (void) pickerTapped:(UITapGestureRecognizer*)gestureRecognizer
{
    CGPoint location = [gestureRecognizer locationInView:self.pickerView];

    CGFloat halfViewHeight = self.pickerView.frame.size.height / 2;

    NSInteger row = -1;
    if (location.y < halfViewHeight - 22
        && location.y > halfViewHeight - 66)
    {
        row = [self.pickerView selectedRowInComponent:0] - 1;
    }
    else if (location.y < halfViewHeight + 22
             && location.y > halfViewHeight - 22)
    {
        row = [self.pickerView selectedRowInComponent:0];
    }
    else if (location.y < halfViewHeight + 66
             && location.y > halfViewHeight + 22)
    {
        row = [self.pickerView selectedRowInComponent:0] + 1;
    }

    if (row >= 0 && row < [self.content count])
    {
        id element = [self.content objectAtIndex:row];

        if (element)
        {
            [self.pickerView selectRow:row inComponent:0 animated:YES];

            // do more stuff
        }
    }
}

回答4:

I have a relatively simple solution to this problem that has worked well for me. Using a hidden custom button you can achieve the tap functionality without a gesture recogniser. This solution works for a picker with one component, however I'm sure it could be adapted to work with more.

Firstly add a button, either in the Interface Builder or programatically. Make it hidden and as wide as the picker then place it so that it sits exactly in the centre of the picker and also in front of it in the view hierarchy.

I'm using an IBAction like this to show my picker. However it's really up to you how you show and hide the picker.

- (IBAction)showPicker:(id)sender
{
    _picker.hidden = NO;
    _buttonPicker.hidden = NO;
}

All the action for choosing the picker value happens in an IBAction for the UIControlEventTouchUpInside event, something like this.

- (IBAction)selectPicker:(id)sender
{
    //Hide the button so that it doesn't get in the way
    _buttonPicker.hidden = YES;

    //Make sure we're within range
    NSInteger max = _values.count;
    NSInteger row = [_picker selectedRowInComponent:0];
    if(row >= 0 && row < max) {
        NSString *value = [_values objectAtIndex:row];

        //Set the label value and hide the picker
        _label.text = value;
        _picker.hidden = YES;
    }
}

I've slightly modified the code for this answer from working code so apologies if it's broken at all.

回答5:

There are only 2 delegates for UIPickerView.

• UIPickerViewDelegate
• UIPickerViewDataSource

So, we can use only 7 methods to control UIPickerView by delegate.

– pickerView:rowHeightForComponent:
– pickerView:widthForComponent:
– pickerView:titleForRow:forComponent:
– pickerView:viewForRow:forComponent:reusingView:
– pickerView:didSelectRow:inComponent:
– numberOfComponentsInPickerView:
– pickerView:numberOfRowsInComponent:

that'all.

In UITableViewDelegate case, there are more methods for UITableView for managing selections. such as, – tableView:willSelectRowAtIndexPath:
– tableView:didSelectRowAtIndexPath:
– tableView:willDeselectRowAtIndexPath:
– tableView:didDeselectRowAtIndexPath:

However...

In UIPickerViewDelegate case, there is only 1 method for responding to row selection.

– pickerView:didSelectRow:inComponent:

来源：https://stackoverflow.com/questions/2403262/allowing-user-to-select-a-uipickerview-row-by-tapping