在点和手指之间形成一条恒定线

Question

我想做一个与Scalar应用程序类似的东西，在那里他们能够从一个点拖到记事本上，将数字粘贴到他们拖动点的位置。我真正感兴趣的是与点和手指保持连接的线，如下所示：

我的问题是我真的不知道这叫什么，所以我很难找到如何做到这一点。有谁知道这将被称为什么，他们有关于这个主题的任何教程？如果你有一些代码供我查看，那就更好了。

感谢。

Answer 1

它将涉及子类化UIView并实现touchesBegan和touchesMoved方法，并在视图子类drawRect方法中绘制一条线，从初始触摸到当前触摸。

继承人之前的问题将有助How do I draw a line on the iPhone?

您只需要更改以下内容，以便坐标是您从触摸方法获得的初始触摸和当前触摸的坐标

CGContextMoveToPoint(c, 5.0f, 5.0f);
CGContextAddLineToPoint(c, 50.0f, 50.0f);

然后在[self setNeedsDisplay];方法中调用touchesMoved会重新绘制线条，以便在移动时跟随您的手指。

然后在手指抬起时为代码实施touchesEnded。

Hoope有帮助！

Answer 2

这个UIView的示例在手指被拖动并且检测到要触摸的第一个视图时绘制线条可以帮助您开始。

//this goes in the header file called "UILineView.h"

#import <UIKit/UIKit.h>

@interface UILineView : UIView

@end

//this in the implementation file called "UILineView.m"

#import "UILineView.h"

@implementation UILineView

{
    CGPoint _originOfTouchPoint; // your fist touch detected in touchesBegan: method
    CGPoint _currentFingerPositionPoint; // the position you have dragged your finger to
    CGFloat _strokeWidth; // the width of the line you wish to draw
    id _touchStartedObject; // the object(UIView) that the first touch was detected on
}

// If you use Interface Builder to design your interface, Objects in a nib file are reconstituted and then initialized using
// their initWithCoder: method
- (id)initWithCoder:(NSCoder *)decoder
{
    self = [super initWithCoder:decoder];
    if (self) {
        // Initialization code
        _originOfTouchPoint = CGPointMake( 0.0, 0.0 );
        _currentFingerPositionPoint = CGPointMake( 100.0, 100.0 );
        _strokeWidth = 2.0;
    }
    return self;
}
/*
// Use initWithFrame if you are not loding the UIView from a nib file
- (id)initWithFrame:(CGRect)frame
{
    self = [super initWithFrame:frame];
    if (self) {
        // Initialization code
        _originOfTouchPoint = CGPointMake( 0.0, 0.0 );
        _currentFingerPositionPoint = CGPointMake( 100.0, 100.0 );
        _strokeWidth = 2.0;
    }
    return self;
}
*/

// Only override drawRect: if you perform custom drawing.
// An empty implementation adversely affects performance during animation.
- (void)drawRect:(CGRect)rect
{
    CGContextRef context    = UIGraphicsGetCurrentContext();
    CGContextSetStrokeColorWithColor( context, [UIColor blueColor].CGColor );
    CGContextSetLineWidth( context, _strokeWidth );
    // fisrt point of line
    CGContextMoveToPoint( context, _originOfTouchPoint.x, _originOfTouchPoint.y );
    // last point of line
    CGContextAddLineToPoint( context, _currentFingerPositionPoint.x, _currentFingerPositionPoint.y );
    // draw the line
    CGContextStrokePath( context );
}

#pragma mark touches

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
    // get starting point and first view touched (if you need to send that view messages)
    _originOfTouchPoint = [[touches anyObject] locationInView:self];
    _touchStartedObject = [[touches anyObject] view];
}
- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
{
    CGPoint movedToPoint = [[touches anyObject] locationInView:self];
    // if moved to a new point redraw the line 
    if ( CGPointEqualToPoint( movedToPoint, _currentFingerPositionPoint ) == NO )
    {
        _currentFingerPositionPoint = movedToPoint;
        // calls drawRect: method to show updated line
        [self setNeedsDisplay];
    }
}
- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event
{
    // reset values
    _originOfTouchPoint = CGPointZero;
    _currentFingerPositionPoint = CGPointZero;
    _touchStartedObject = nil;
}

@end

Answer 3

UIGestureRecognizer可以做到这一点，而不会将触摸和拖动逻辑与视图混淆。我用它们来编辑地图上的形状，长按拖动等。请参阅this tutorial。