如何在 Xcode 中跟踪多次触摸

Question

最近我正在制作一个可以同时拖动多个对象的应用程序。我曾尝试使用UIPanGestureRecognizer 来获取手指触摸的坐标，但我不知道哪个触摸属于哪个手指。

我需要使用 Objective-C 支持四个手指同时平移而不会相互干扰。

我已经搜索了一段时间的解决方案，但他们显示的答案对我不起作用。任何帮助将不胜感激。

Answer 1

我在同一个问题上苦苦挣扎了很长时间，终于解决了。以下是我的DrawView.m中的代码，它是UIView的子类，可以支持使用drawRect:进行绘图。

#import "DrawView.h"

#define MAX_TOUCHES 4

@interface DrawView() {

    bool touchInRect[MAX_TOUCHES];
    CGRect rects[MAX_TOUCHES];
    UITouch *savedTouches[MAX_TOUCHES];
}

@end

@implementation DrawView

-(id)initWithCoder:(NSCoder *)aDecoder {
    self = [super initWithCoder:aDecoder];
    if (self) {
        // Initialization code
        self.multipleTouchEnabled = YES;
        for (int i=0; i<MAX_TOUCHES; i++) {
            rects[i] = CGRectMake(200, 200, 50 ,50);
            savedTouches[i] = NULL;
            touchInRect[i] = false;
        }
    }
    return self;
}

- (void)drawRect:(CGRect)rect {
    // Drawing code
    [[UIColor blueColor] set];
    CGContextRef context = UIGraphicsGetCurrentContext();

    for (int i=0; i<MAX_TOUCHES; i++) {
        CGContextFillRect(context, rects[i]);
        CGContextStrokePath(context);
    }
}

#pragma mark - Handle Touches

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

    NSArray *allTouches = [touches allObjects];
    for (int i=0; i<[allTouches count]; i++) {
        UITouch *touch = allTouches[i];
        CGPoint newPoint = [touch locationInView:self];

        for (int j=0; j<MAX_TOUCHES; j++) {
            if (CGRectContainsPoint(rects[j], newPoint) && !touchInRect[j]) {
                touchInRect[j] = true;
                savedTouches[j] = touch;
                break;
            }
        }
    }
}

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

    NSArray *allTouches = [touches allObjects];
    for (int i=0; i<[allTouches count]; i++) {
        UITouch *touch = allTouches[i];
        CGPoint newPoint = [touch locationInView:self];

        for (int j=0; j<MAX_TOUCHES; j++) {
            if (touch == savedTouches[j]) {
                rects[j] = [self rectWithSize:rects[j].size andCenter:newPoint];
                [self setNeedsDisplay];
                break;
            }
        }
    }
}

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

    NSArray *allTouches = [touches allObjects];
    for (int i=0; i<[allTouches count]; i++) {
        UITouch *touch = allTouches[i];

        for (int j=0; j<MAX_TOUCHES; j++) {
            if (touch == savedTouches[j]) {
                touchInRect[j] = false;
                savedTouches[j] = NULL;
                break;
            }
        }
    }
}


- (CGRect)rectWithSize:(CGSize)size andCenter:(CGPoint)point {
    return CGRectMake(point.x - size.width/2, point.y - size.height/2, size.width, size.height);
}

@end

我将MAX_TOUCHES 设置为4，所以屏幕上会有四个对象。其基本概念是在调用touchesBegan:: 时将每个UITouch ID 存储在savedTouches 数组中，然后在调用touchesMoved:: 时将每个ID 与屏幕上的触摸进行比较。

只需将代码粘贴到您的.m 文件中即可。示例结果如下所示：

希望这会有所帮助:)