動畫-CAShapeLayer實現QQ消息紅點拖拽效果

CAShapeLayer

一言以蔽之：CAShapeLayer 能夠根據貝塞爾曲線描繪出的路徑而生成對應的圖形

綜合例子

• 效果圖

• 關鍵技術點剖析

• 分析 QQ 粘性動畫的關鍵點就是當手勢拖動時候2個圓之間那個形狀怎麼繪製

答案：將2個圓的某一時刻之間造成的形狀用數學抽象來計算。

• 拖動到超過某個範圍的時候怎麼執行爆炸動畫

UIImageView 能夠執行幀動畫，相似於 Flash 效果

關鍵代碼

- (void)pan:(UIPanGestureRecognizer *)pan{
    //當前移動的偏移量
    CGPoint transP = [pan translationInView:self];
    //改變紅點的位置
    //transform並無修改自身的 center（center 是 layer 的position），只是修改了 frame
    NSLog(@"偏移量:%@",NSStringFromCGPoint(transP));
    CGPoint center = self.center;
    center.x += transP.x;
    center.y += transP.y;
    self.center = center;
    
    //self.transform = CGAffineTransformTranslate(self.transform, transP.x, transP.y);
    //手勢復位:設置座標原點位上次的座標
    [pan setTranslation:CGPointZero inView:self];
    
    CGFloat distance = [self distanceWith:self.smallCircle bigCircle:self];
    NSLog(@"%f",distance);
    
    
    CGFloat smallCircleRadius = self.bounds.size.width * 0.5;
    smallCircleRadius = smallCircleRadius - distance/10;
    
    if (smallCircleRadius < 3) {
        smallCircleRadius = 3;
    }
    self.smallCircle.bounds = CGRectMake(0, 0, smallCircleRadius*2, smallCircleRadius*2);
    self.smallCircle.layer.cornerRadius = smallCircleRadius;
    
    if (self.smallCircle.hidden == NO) {
        //返回一個不規則的路徑
        UIBezierPath *path = [self drawTracertWithSmallCircle:self.smallCircle bigCircle:self];
        //將形狀轉換爲一個形狀圖層
        self.shapeLayer.path = path.CGPath;//根據路徑生成形狀
    }
    //建立形狀圖層
    [self.superview.layer insertSublayer:self.shapeLayer atIndex:0];
    
    if (distance > 60) {
        self.smallCircle.hidden = YES;
        [self.shapeLayer removeFromSuperlayer];
    }
    
    if (pan.state == UIGestureRecognizerStateEnded) {
        //結束手勢
        if (distance < 60) {
            [self.shapeLayer removeFromSuperlayer];
            self.center = self.smallCircle.center;
            self.smallCircle.hidden = NO;
        }
        else{
            //手勢拖拽超過60則播放一個動畫
            UIImageView *imageView = [[UIImageView alloc] initWithFrame:self.bounds];
            
            NSMutableArray *images = [NSMutableArray array];
            
            for (int i=0; i<8; i++) {
                NSString *imageName = [NSString stringWithFormat:@"%d",i+1];
                UIImage *image = [UIImage imageNamed:imageName];
                [images addObject:image];
            }
            imageView.animationImages = images;
            [imageView setAnimationDuration:1];
            [imageView startAnimating];
            [self addSubview:imageView];
            //動畫結束移除自己
            dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(1 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
                [self removeFromSuperview];
            });
        }
    }
    
}


- (CGFloat )distanceWith:(UIView *)smallCircle bigCircle:(UIView *)bigScirle{
    CGFloat offsetX = bigScirle.frame.origin.x - smallCircle.frame.origin.x;
    CGFloat offsetY = bigScirle.frame.origin.y - smallCircle.frame.origin.y;
    return sqrt( pow(offsetX, 2) + pow(offsetY, 2));
}

//將2個圓運行的變化軌跡用代碼模擬
- (UIBezierPath *)drawTracertWithSmallCircle:(UIView *)smallCircle bigCircle:(UIView *)bigCircle{
    
    CGFloat X1 = smallCircle.center.x;
    CGFloat X2 = bigCircle.center.x;
    CGFloat Y1 = smallCircle.center.y;
    CGFloat Y2 = bigCircle.center.y;
    
    CGFloat r1 = smallCircle.bounds.size.width/2;
    CGFloat r2 = bigCircle.bounds.size.width/2;
    
    CGFloat d = [self distanceWith:smallCircle bigCircle:bigCircle];
    //Ø 表明角度
    CGFloat SinØ = (X2 - X1)/d;
    CGFloat CosØ = (Y2 - Y1)/d;
    
    CGPoint pointA = CGPointMake(X1 - r1*CosØ, Y1 + r1*SinØ);

    CGPoint pointB = CGPointMake(X1 + r1*CosØ, Y1 - r1*SinØ);
    
    CGPoint pointC = CGPointMake(X2 + r2*CosØ, Y2 - r2*SinØ);
    
    CGPoint pointD = CGPointMake(X2 - r2*CosØ, Y2 + r2*SinØ);
    
    CGPoint pointO = CGPointMake(X1 + SinØ *d/2, Y1 + CosØ*d/2);
    
    CGPoint pointP = CGPointMake(X1 + SinØ *d/2,Y1 + CosØ*d/2 );

    //描述路徑
    UIBezierPath *path = [UIBezierPath bezierPath];
    
    //AB
    [path moveToPoint:pointA];
    [path addLineToPoint:pointB];
    
    //BC(曲線)
    [path addQuadCurveToPoint:pointC controlPoint:pointP];
    
    //CD
    [path addLineToPoint:pointD];
    
    //DA(曲線)
    [path addQuadCurveToPoint:pointA controlPoint:pointO];
    
    return path;
}

完整的代碼，Github地址