如何在触摸事件上画线?

问题描述

嘿，我是 Objective C 的初学者，请帮帮我

Hey i m beginner of objective C Please Help me

我做了以下代码，但不起作用.....

i make following code but not work.....

-(void) touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{

UITouch *touch = [touches anyObject];
if ([touch view] == self.view) {

    CGPoint location = [touch locationInView:self.view];
    loc1 = location;
    CGContextMoveToPoint(context, location.x, location.y);
    NSLog(@"x:%d y:%d At Touch Begain", loc1.x, loc1.y);
}
}
- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event

{
    UITouch *touch = [touches anyObject];

        if ([touch view] == self.view)
    {
    CGPoint location = [touch locationInView:self.view];
    CGContextMoveToPoint(context, loc1.x, loc1.y);
    NSLog(@"x:%d y:%d At Touch Move", loc1.x, loc1.y);
    CGContextAddLineToPoint(context, location.x, location.y);
    NSLog(@"x:%d y:%d", location.x, location.y);
}

}

我在 viewdidload 方法中声明了 contex，并尝试在触摸事件中声明但不起作用...

i declare contex in viewdidload method and also try to declare in touch event but not work...

我的应用日志文件看起来像...

My app Log file look like...

x:0 y:1079934976 At Touch Move 周四 1 月 13 日 11:20:05 .local拖放[536]:

CGContextAddLineToPoint: 无效上下文 0x0 2011-01-13 11:20:05.149DragDrop[536:207] x:0 y:1079902208 Thu Jan 13 11:20:05 .local拖放[536]:

CGContextAddLineToPoint: invalid context 0x0 2011-01-13 11:20:05.149 DragDrop[536:207] x:0 y:1079902208 Thu Jan 13 11:20:05 .local DragDrop[536] :

CGContextSetRGBStrokeColor: 无效上下文 0x0 Thu Jan 13 11:20:05.local 拖放[536]:

CGContextSetRGBStrokeColor: invalid context 0x0 Thu Jan 13 11:20:05 .local DragDrop[536] :

CGContextDrawPath: 无效上下文 0x0 Thu Jan 13 11:20:05 .local拖放[536]:

CGContextDrawPath: invalid context 0x0 Thu Jan 13 11:20:05 .local DragDrop[536] :

CGContextMoveToPoint: 无效上下文 0x0 2011-01-13 11:20:05.199DragDrop[536:207] x:0 y:1079934976 At Touch Move Jan 13 Thu 11:20:05.local 拖放[536]:

CGContextMoveToPoint: invalid context 0x0 2011-01-13 11:20:05.199 DragDrop[536:207] x:0 y:1079934976 At Touch Move Thu Jan 13 11:20:05 .local DragDrop[536] :

CGContextAddLineToPoint: 无效上下文 0x0 2011-01-13 11:20:05.200拖放[536:207] x:0 y:1079885824

CGContextAddLineToPoint: invalid context 0x0 2011-01-13 11:20:05.200 DragDrop[536:207] x:0 y:1079885824

推荐答案

您通常不会在触摸检测方法中直接绘图.通常，您只需在此处存储新的点/线，然后将它们全部绘制在 drawRect: 中.假设您有一个 UIView 的自定义子类，它有一个类型为 NSMutableArray 的实例变量 paths 和一个属性 currentPathUIBezierPath 类型.然后，您可以大致像这样实现触摸检测和 drawRect 方法:

You typically don't draw directly in the touch detection methods.Usually, you'd just store new points/lines there and draw all of them in drawRect:. Let's assume you have a custom subclass of UIView which has an instance variable paths of type NSMutableArray and a property currentPath of type UIBezierPath. You could then implement the touch detection and drawRect methods roughly like this:

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
  self.currentPath = [UIBezierPath bezierPath];
  currentPath.lineWidth = 3.0;
  [currentPath moveToPoint:[touch locationInView:self]];
  [paths addObject:self.currentPath];
}

- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event {
  [self.currentPath addLineToPoint:[touch locationInView:self]];
  [self setNeedsDisplay];
}

- (void)drawRect:(CGRect)rect {
  [[UIColor redColor] set];
  for (UIBezierPath *path in paths) {
    [path stroke];
  }
}

请注意，这被简化了很多.如果你画了很多线，性能会受到影响，最终，你会希望将绘图缓存在位图图像中，但这应该可以帮助你开始.

Note that this is simplified a lot. If you draw many lines, performance will suffer and eventually, you'll want to cache the drawing in a bitmap image, but this should get you started.

这篇关于如何在触摸事件上画线?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！