如何在分段控制按钮中永久取消选择分段，直到再次单击它

问题描述

我有一个有 4 个段的 UISegmentedControl.当它被选中时，它应该保持选中状态.当再次单击同一段时，它应该取消选择自身.如何做到这一点?

I have a UISegmentedControl with 4 segments. When it is selected, it should maintain the selected state. When the same segment is clicked again, it should deselect itself. How to achieve this?

推荐答案

由于 UISegmentedControl 只在未选中段被选中时发送动作，所以你必须继承 UISegmentedControl对其触摸处理进行微小的更改.我使用这个类:

Since UISegmentedControl only sends an action if a not selected segment is selected, you have to subclass UISegmentedControl to make a tiny change in its touch handling. I use this class:

@implementation MBSegmentedControl

// this sends a value changed event even if we reselect the currently selected segment
- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
    NSInteger current = self.selectedSegmentIndex;
    [super touchesBegan:touches withEvent:event];
    if (current == self.selectedSegmentIndex) {
        [self sendActionsForControlEvents:UIControlEventValueChanged];
    }
}

@end

现在您将获得 UIControlEventValueChanged 事件，即使该段已被选中.只需将当前索引保存在变量中并在操作中进行比较.如果两个索引匹配，您必须取消选择触摸的段.

Now you will get UIControlEventValueChanged events even if the segment is already selected. Simply save the current index in a variable and compare it in the action. If the two indexes match you have to unselect the touched segment.

// _selectedSegmentIndex is an instance variable of the view controller

- (void)viewWillAppear:(BOOL)animated {
    [super viewWillAppear:animated];
    _selectedSegmentIndex = self.segment.selectedSegmentIndex;
}

- (IBAction)segmentChanged:(UISegmentedControl *)sender {
    if (sender.selectedSegmentIndex == _selectedSegmentIndex) {
        NSLog(@"Segment %d deselected", sender.selectedSegmentIndex);
        sender.selectedSegmentIndex =  UISegmentedControlNoSegment;
        _selectedSegmentIndex = UISegmentedControlNoSegment;
    }
    else {
        NSLog(@"Segment %d selected", sender.selectedSegmentIndex);
        _selectedSegmentIndex = sender.selectedSegmentIndex;
    }
}

<小时>

iOS 7 更改了 UISegmentedControl 的触摸处理方式.selectedSegmentIndex 现在在 touchesEnded: 期间更改.

所以更新后的子类应该是这样的:

So the updated Subclass should look like this:

@implementation MBSegmentedControl

+ (BOOL)isIOS7 {
    static BOOL isIOS7 = NO;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        NSInteger deviceSystemMajorVersion = [[[[[UIDevice currentDevice] systemVersion] componentsSeparatedByString:@"."] objectAtIndex:0] integerValue];
        if (deviceSystemMajorVersion >= 7) {
            isIOS7 = YES;
        }
        else {
            isIOS7 = NO;
        }
    });
    return isIOS7;
}

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
    NSInteger previousSelectedSegmentIndex = self.selectedSegmentIndex;
    [super touchesBegan:touches withEvent:event];
    if (![[self class] isIOS7]) {
        // before iOS7 the segment is selected in touchesBegan
        if (previousSelectedSegmentIndex == self.selectedSegmentIndex) {
            // if the selectedSegmentIndex before the selection process is equal to the selectedSegmentIndex
            // after the selection process the superclass won't send a UIControlEventValueChanged event.
            // So we have to do this ourselves.
            [self sendActionsForControlEvents:UIControlEventValueChanged];
        }
    }
}

- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event {
    NSInteger previousSelectedSegmentIndex = self.selectedSegmentIndex;
    [super touchesEnded:touches withEvent:event];
    if ([[self class] isIOS7]) {
        // on iOS7 the segment is selected in touchesEnded
        if (previousSelectedSegmentIndex == self.selectedSegmentIndex) {
            [self sendActionsForControlEvents:UIControlEventValueChanged];
        }
    }
}

@end

<小时>

Swift 2.2 版本，修复了 Grzegorz 注意到的问题.

Swift 2.2 version, fixed the problem Grzegorz noticed.

class ReselectableSegmentedControl: UISegmentedControl {
    @IBInspectable var allowReselection: Bool = true

    override func touchesEnded(touches: Set<UITouch>, withEvent event: UIEvent?) {
        let previousSelectedSegmentIndex = self.selectedSegmentIndex
        super.touchesEnded(touches, withEvent: event)
        if allowReselection && previousSelectedSegmentIndex == self.selectedSegmentIndex {
            if let touch = touches.first {
                let touchLocation = touch.locationInView(self)
                if CGRectContainsPoint(bounds, touchLocation) {
                    self.sendActionsForControlEvents(.ValueChanged)
                }
            }
        }
    }
}

<小时>

Swift 3.0 对此进行了修改，如下所示:

Swift 3.0 changes the fix for this to look like the following:

class MyDeselectableSegmentedControl: UISegmentedControl {
    override func touchesEnded(_ touches: Set<UITouch>, with event: UIEvent?) {
        let previousIndex = selectedSegmentIndex

        super.touchesEnded(touches, with: event)

        if previousIndex == selectedSegmentIndex {
            let touchLocation = touches.first!.location(in: self)

            if bounds.contains(touchLocation) {
                sendActions(for: .valueChanged)
            }
        }
    }
}

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