此篇文章將要引見IOS動畫案例(1) 相似於qq賬號信息裡的一個動畫的相關內容，詳細內容請看上面

   受人所托，做一個相似於qq賬號信息裡的一個動畫，覺得挺有意思，也沒覺得有多難，就開端做了，後果才發現學的數學知識都還給體育教師了，研討了大半天賦做出來。    先看一下動畫效果：

  用到的知識點： (1)三角函數 (2)CALayer (3)CATransaction (4)UIBezierPath (5)CAKeyframeAnimation (6)CAAnimationGroup

   如圖，這分明是一段圓弧，那麼要確定這段一段圓弧的地位，就得確定這段圓弧的圓心和圓心角。我規則圓心在手機屏幕的左頂點，也就是（0，0），圓心角為60°。別問我為什麼這麼確定，我也是一點點嘗試的。我們先設手機屏幕的寬度為 ScreenWidth，圓弧半徑為R；那麼R = ScreenWidth/cos(60°)；知道了這些開端畫圓弧。

    // 屏幕的寬度
    CGFloat width = [UIScreen mainScreen].bounds.size.width;
    // 圓半徑 
    float r = 2 * width / sqrt(3);
    // 畫曲線
    UIColor *color = [UIColor redColor];
    [color set];
    UIBezierPath *path = [UIBezierPath bezierPathWithArcCenter:CGPointMake(0, 0) radius:r startAngle:M_PI / 2 endAngle:M_PI / 6 clockwise:NO];
    path.lineWidth = 1.0;
    path.lineCapStyle = kCGLineCapRound;
    path.lineJoinStyle = kCGLineJoinRound;
    [path stroke];

   確定了圓心角和半徑就要確定ABCD四個點的坐標了，辨別作為四張圖片的圓心。圓弧SA和圓弧DE的圓心角一樣，設定為7.5°，那麼弧AB、弧BC、弧CD的圓心角設定為相等，辨別為（60 - 7.5 * 2）/ 3 = 15°。那麼A點的坐標就等於（R * sin7.5，R * cos7.5°）；B,C,D點的坐標一樣用三角函數求，辨別為（R * sin22.5，R * cos22.5°）,（R * sin37.5，R * cos37.5°）,（R * sin52.5，R * cos52.5°）。ABCD其實都是一個按鈕，上面開端放按鈕。

// 放圖片
    for (int i = 0; i < 4; i++) {
    
        // 一共四個按鈕 從左到右index辨別為0，1，2，3
        UIButton *button = [UIButton buttonWithType:UIButtonTypeCustom];
        button.frame = [self getButtonFrame:i];
        button.tag = i + 1;
        [button addTarget:self action:@selector(buttonClick:) forControlEvents:UIControlEventTouchUpInside];
        [button setImage:[UIImage imageNamed:[NSString stringWithFormat:@"%d",i + 1]] forState:UIControlStateNormal];
        // 設置按鈕為圓
        button.layer.cornerRadius = 25;
        button.layer.borderColor = [UIColor greenColor].CGColor;
        button.layer.masksToBounds = YES;
        button.layer.borderWidth = 2.0f;
        [self addSubview:button];
    }
    // 依據Index確定按鈕的坐標
    - (CGRect)getButtonFrame: (int) index {
    
    float radians = M_PI * (7.5 + 15 * index) / 180;
    CGFloat width = [UIScreen mainScreen].bounds.size.width;
    float r = 2 * width / sqrt(3);
    CGRect frame = CGRectMake(sin(radians) * r, cos(radians) * r, 50, 50);
    frame.origin.x = frame.origin.x - 25;
    frame.origin.y = frame.origin.y - 25;
    return frame;
 }

   頭像默許放第一個。

    self.head = [[UIImageView alloc] initWithFrame:[self getButtonFrame:0]];
    self.head.image = [UIImage imageNamed:@"myHead"];
    self.head.layer.borderColor = [UIColor greenColor].CGColor;
    self.head.layer.masksToBounds = YES;
    self.head.layer.cornerRadius = 25;
    self.head.layer.borderWidth = 2.0f;
    [self addSubview:self.head];

   之後按鈕點擊之後，頭像挪動到按鈕點擊的中央。

// 按鈕點擊事情
- (void)buttonClick:(UIButton *)button {
    
    // 原來圖片所在按鈕的index
    int preIndex = [self getPreviousIndexByFrame:self.head.frame];
    int buttonIndex = (int)button.tag - 1;
    // 點擊圖片所在按鈕 不做任何操作
    if (preIndex == buttonIndex) {
        return;
    }
    CGFloat width = [UIScreen mainScreen].bounds.size.width;
    float r = 2 * width / sqrt(3);
    //參加動畫效果
    CALayer *transitionLayer = [[CALayer alloc] init];
    
    [CATransaction begin];
    //顯式事務默許開啟動畫效果,kCFBooleanTrue封閉 保證begin和commit 之間的屬性修正同時停止
    [CATransaction setValue:(id)kCFBooleanFalse forKey:kCATransactionDisableActions];
     [CATransaction setDisableActions:NO];
    transitionLayer.opacity = 1.0;
    transitionLayer.contents = self.head.layer.contents;
    transitionLayer.borderColor = [UIColor greenColor].CGColor;
    transitionLayer.masksToBounds = YES;
    transitionLayer.cornerRadius = 25;
    transitionLayer.borderWidth = 2.0f;
    transitionLayer.frame = self.head.frame;//[self convertRect:self.head.bounds toView:self.head];
    self.head.hidden = YES;
    transitionLayer.backgroundColor=[UIColor blueColor].CGColor;
    [self.layer addSublayer:transitionLayer];
    [CATransaction commit];
    
    UIBezierPath *movePath;
    //途徑曲線 貝塞爾曲線
    if (buttonIndex > preIndex) {
        // 向上滑 逆時針
        movePath = [UIBezierPath bezierPathWithArcCenter:CGPointMake(0, 0) radius:r startAngle:[self getAnticlockwiseByIndex:preIndex] endAngle:[self getAnticlockwiseByIndex:buttonIndex] clockwise:NO];
        [movePath moveToPoint:transitionLayer.position];
    }else {
        // 向下滑 順時針
        movePath = [UIBezierPath bezierPathWithArcCenter:CGPointMake(0, 0) radius:r startAngle:[self getClockwiseAngleByIndex:preIndex] endAngle:[self getClockwiseAngleByIndex:buttonIndex] clockwise:YES];
        [movePath moveToPoint:transitionLayer.position];
    }
    //關鍵幀動畫效果
    CAKeyframeAnimation *positionAnimation = [CAKeyframeAnimation animationWithKeyPath:@"position"];
    positionAnimation.path = movePath.CGPath;
    positionAnimation.removedOnCompletion = YES;
    
    CAAnimationGroup *group = [CAAnimationGroup animation];
    group.beginTime = CACurrentMediaTime();
    CGFloat time = 0.7 * labs(buttonIndex - preIndex);
    group.duration = time;
    group.animations = [NSArray arrayWithObjects:positionAnimation,nil];
    group.timingFunction=[CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionEaSEOut];
    group.fillMode = kCAFillModeForwards;
    group.removedOnCompletion = NO;
    group.autoreverses= NO;
    
    [transitionLayer addAnimation:group forKey:@"opacity"];
    [CATransaction setCompletionBlock:^{
        [NSThread sleepForTimeInterval:time];
        [transitionLayer removeFromSuperlayer];
        self.head.hidden = NO;
        self.head.frame = button.frame;
    }];
}
// 依據Index取得順時針的弧度
- (float)getAnticlockwiseByIndex: (NSInteger)index {
    
    return M_PI * (0.5  - (7.5 + 15 * index) / 180);
}
// 依據Index取得逆時針的弧度
- (float)getClockwiseAngleByIndex: (NSInteger)index {
    
    index = 3 - index;
    return M_PI * (30 + 7.5 + 15 * index) / 180;
}

   這個動畫的難點其實是確定四個按鈕的坐標以及圓弧的半徑，次要是學的數學都忘的差不多了，還好重新撿起來還算不難。 

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