如何在分段控制按钮中永久取消选择分段，直到再次单击为止

我有一个UISegmentedControl，它有4个段。选择时，应保持selected state。当再次单击同一段时，它应该是deselect itself。如何做到这一点？

由于UISegmentedControl只有在选择了未选择的分段时才会发送动作，因此必须对UISegmentedControl进行子类化，以对其触摸处理进行微小更改。我使用这个类：

@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，即使已经选择了分段，也将获得UIControlEventValueChanged事件。只需将当前索引保存在变量中，然后在操作中进行比较。如果两个索引匹配，则必须取消选择所触摸的线段。

// _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;
    }
}

iOS 7改变了UISegmentedControl的触摸处理方式。选定的SegmentIndex现在在touchesEnded:期间发生更改。

所以更新后的子类应该是这样的：

@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

Swift 2.2版本，修复了Grzegorz注意到的问题。

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)
                }
            }
        }
    }
}

Swift 3.0对此进行了修改，如下所示：

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)
            }
        }
    }
}

这里有一个问题的解决方案，当你试图通过点击UISegmentControl来取消选择，然后你完成触摸外部时，它仍然会取消选择。

- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event
{
CGPoint locationPoint = [[touches anyObject] locationInView:self];
CGPoint viewPoint = [self convertPoint:locationPoint fromView:self];
if ([self pointInside:viewPoint withEvent:event]) {
    int oldValue = self.selectedSegmentIndex;
    [super touchesEnded:touches withEvent:event];
    if (oldValue == self.selectedSegmentIndex)
    {
        [super setSelectedSegmentIndex:UISegmentedControlNoSegment];
        [self sendActionsForControlEvents:UIControlEventValueChanged];
    }
}
}

您可以使用以下方法（感谢Grzegorz和Matthias的回答）：

- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event {
    NSInteger previousSelectedSegmentIndex = self.selectedSegmentIndex;
    [super touchesEnded:touches withEvent:event];
    CGPoint locationPoint = [[touches anyObject] locationInView:self];
    CGPoint viewPoint = [self convertPoint:locationPoint fromView:self];
    if ([self pointInside:viewPoint withEvent:event] && previousSelectedSegmentIndex == self.selectedSegmentIndex) {
        self.selectedSegmentIndex = UISegmentedControlNoSegment;
        [self sendActionsForControlEvents:UIControlEventValueChanged];
    }
}

我制作了一个开源（麻省理工学院许可）类STASegmentedControl（支持iOS 7+），它包含了这一功能（以及更多）。

参考@Matthias Bauch发布的答案。我不得不根据Xcode 7.3:中的Swift 2.2进行一些更改

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)
                }
            }
        }
    }
}

swift3.1版本由@Kushal Ashok 发布

class ReselectableSegmentedControl: UISegmentedControl {
    @IBInspectable var allowReselection: Bool = true
    override func touchesEnded(_ touches: Set<UITouch>, with event: UIEvent?) {
        let previousSelectedSegmentIndex = self.selectedSegmentIndex
        super.touchesEnded(touches, with: event)
        if allowReselection && previousSelectedSegmentIndex == self.selectedSegmentIndex {
            if let touch = touches.first {
                let touchLocation = touch.location(in: self)
                if bounds.contains(touchLocation) {
                    self.sendActions(for: .valueChanged)
                }
            }
        }
    }
}

这里有一个独立于IOS版本的解决方案。这是行为本身的选择。

@interface CustomSegmentedControl : UISegmentedControl
@end


@implementation CustomSegmentedControl{

BOOL _touchBegan;
BOOL _reactOnTouchBegan;
}

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
    _touchBegan = YES;
    NSInteger previousSelectedSegmentIndex = self.selectedSegmentIndex;
    [super touchesBegan:touches withEvent:event];
    if (_reactOnTouchBegan) {
        // before iOS7 the segment is selected in touchesBegan
        if (previousSelectedSegmentIndex == self.selectedSegmentIndex) {
            [self sendActionsForControlEvents:UIControlEventValueChanged];
        }
    }
}

-(void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event {
    _touchBegan = NO;
    NSInteger previousSelectedSegmentIndex = self.selectedSegmentIndex;
    [super touchesEnded:touches withEvent:event];
    if (!_reactOnTouchBegan) {
        CGPoint locationPoint = [[touches anyObject] locationInView:self];
        CGPoint viewPoint = [self convertPoint:locationPoint fromView:self];
        if ([self pointInside:viewPoint withEvent:event]) {
            // on iOS7 the segment is selected in touchesEnded
            if (previousSelectedSegmentIndex == self.selectedSegmentIndex) {
                [self sendActionsForControlEvents:UIControlEventValueChanged];
            }
        }
    }
}

- (void)sendActionsForControlEvents:(UIControlEvents)controlEvents {
    if(controlEvents == UIControlEventValueChanged){
        _reactOnTouchBegan = _touchBegan;
    }
    [super sendActionsForControlEvents:controlEvents];
}

@end

非常有用！非常感谢。我想对我的项目的事件有更多的控制权，所以我调整了@Matthias的回答，发送了一个自定义的"值不变"事件。我在GitHub上举了一个例子。

我还加入了@Grzegorz的修复程序，这样当用户将手指拖到分段控件之外时，它就会正常工作。

关于@Stunner，这是我为实现目标所做的贡献。我更改了一些内容，并添加了属性_previousSelectedSegmentIndex；在@Stunner代码中，变量previousSelectedSegmentIndex是无用的：

@implementation STASegmentedControl
{
    NSInteger _previousSelectedSegmentIndex;
}
- (void)setSelectedSegmentIndex:(NSInteger)selectedSegmentIndex
{
    [super setSelectedSegmentIndex: selectedSegmentIndex];
    _previousSelectedSegmentIndex = self.selectedSegmentIndex;
}
- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event {
    [super touchesEnded:touches withEvent:event];
    CGPoint locationPoint = [[touches anyObject] locationInView:self];
    CGPoint viewPoint = [self convertPoint:locationPoint fromView:self];
    if (self.toggleableSegments) { // toggle selected segment on/off
        if ([self pointInside:viewPoint withEvent:event] && _previousSelectedSegmentIndex == self.selectedSegmentIndex) {
            self.selectedSegmentIndex = UISegmentedControlNoSegment;
            [self sendActionsForControlEvents:UIControlEventValueChanged];
        }
    }
    _previousSelectedSegmentIndex = self.selectedSegmentIndex;
}

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