objective-c - 在一个点和你的手指之间画一条恒定的线

Question

我想做与 Scalar 应用程序类似的事情，他们可以从一个点拖动到记事本上，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，所以我在寻找如何做到这一点时遇到了麻烦。有谁知道这会被称为什么，有他们遇到过关于这个主题的任何教程吗？如果你有一些代码让我看，那就更好了。

谢谢。

Answer 1

它将涉及子类UIView化和实现touchesBeganand方法，并在您的视图子类方法中从初始触摸到当前触摸touchesMoved画一条线。drawRect

继承人以前的问题，这将有助于我如何在 iPhone 上画一条线？

您只需要更改以下内容，以便坐标是您从 touches 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);

然后调用[self setNeedsDisplay];该touchesMoved方法将在您移动时重新绘制线条以跟随您的手指。

然后touchesEnded在手指抬起时执行代码。

希望它有帮助！

Answer 2

这个 UIView 示例在手指拖动时绘制线条并检测到要触摸的第一个视图应该可以帮助您开始。

//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

AUIGestureRecognizer可以做到这一点，而不会混淆触摸和拖动逻辑与视图。我用它们来编辑地图上的形状、长按拖动等。请参阅本教程。