iOS視圖動畫效果 CPAnimationSequence

編寫iOS視圖UIView的動畫效果需要很多代碼，雖然iOS 4支持塊定義，對視圖動畫的定義減少了不少代碼，但語法依舊不好看。CPAnimationSequence是一個開源代碼庫，可以一種間接快捷的方式來定義描述動畫隊列，克服了寫繁多的代碼。下面一個使用例子：

CPAnimationSequence* shakespeare = [CPAnimationSequence sequenceWithSteps:
    [CPAnimationStep           for:0.2 animate:^{ self.romeo.alpha = 1.0; }],
    [CPAnimationStep           for:0.2 animate:^{ self.julia.alpha = 1.0;  }],
    [CPAnimationStep after:1.0 for:0.7 animate:^{
                            CGPoint love = CGPointMake((self.romeo.center.x + self.julia.center.x)/2,
                                                       (self.romeo.center.y + self.julia.center.y)/2);
                            self.romeo.center = love;
                            self.julia.center = love;
    }],
    [CPAnimationStep after:2.0 for:0.5 animate:^{ self.romeo.alpha = 0.0;
                                                  self.julia.alpha = 0.0; }]
    nil];
[shakespeare run];

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