问ios 9.2 predictedTouchesForTouch:没有文档

EN

@interface ViewController ()

@property (nonatomic, strong) UIBezierPath *path;
@property (nonatomic, weak) CAShapeLayer *pathLayer;
@property (nonatomic, weak) CAShapeLayer *predictedPathLayer;

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];

    // set up layer for the main (non-predicted) path; line blue line

    CAShapeLayer *mainPathLayer = [CAShapeLayer layer];
    mainPathLayer.lineWidth = 1;
    mainPathLayer.strokeColor = [UIColor blueColor].CGColor;
    mainPathLayer.fillColor = [UIColor clearColor].CGColor;
    mainPathLayer.lineCap = kCALineCapRound;
    mainPathLayer.lineJoin = kCALineJoinRound;
    mainPathLayer.frame = self.view.layer.bounds;
    [self.view.layer addSublayer:mainPathLayer];
    self.pathLayer = mainPathLayer;

    // set up layer for the predicted path, if any; thicker red line (just so I can see it clearly)

    CAShapeLayer *predictedPathLayer = [CAShapeLayer layer];
    predictedPathLayer.lineWidth = 5;
    predictedPathLayer.strokeColor = [UIColor redColor].CGColor;
    predictedPathLayer.fillColor = [UIColor clearColor].CGColor;
    predictedPathLayer.lineCap = kCALineCapRound;
    predictedPathLayer.lineJoin = kCALineJoinRound;
    predictedPathLayer.frame = self.view.layer.bounds;
    [self.view.layer addSublayer:predictedPathLayer];
    self.predictedPathLayer = predictedPathLayer;
}

- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event {
    UITouch *touch = [touches anyObject];
    self.path = [UIBezierPath bezierPath];
    [self.path moveToPoint:[touch locationInView:self.view]];
}

- (void)touchesMoved:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event {
    UITouch *touch = [touches anyObject];
    CGPoint location = [touch locationInView:self.view];

    // handle coalesced touches

    NSArray<UITouch *> *coalescedTouches = [event coalescedTouchesForTouch:touch];
    for (UITouch *coalescedTouch in coalescedTouches) {
        location = [coalescedTouch locationInView:self.view];
        [self.path addLineToPoint:location];
    }

    self.pathLayer.path = self.path.CGPath;

    // now handle predicted touches

    UIBezierPath *predictedPath = [UIBezierPath bezierPath];
    [predictedPath moveToPoint:location];
    NSArray<UITouch *> *predictedTouches = [event predictedTouchesForTouch:touch];


    for (UITouch *predictedTouch in predictedTouches) {
        [predictedPath addLineToPoint:[predictedTouch locationInView:self.view]];
    }

    self.predictedPathLayer.path = predictedPath.CGPath;

    // for diagnostic purposes, let's log the count of each; do not do this in production app

    NSLog(@"%ld %ld", [coalescedTouches count], [predictedTouches count]);
}

- (void)touchesEnded:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event {
    self.predictedPathLayer.path = NULL; // discard any predicted path, because that's no longer valid
}

@end