iOS 时钟：SPClockView

SPClockView 特性如下：

1. 可以设置时区，也可以从列表中选择时区

2. 自动检测日间和夜间，转换时钟的背景

3. 不能用 NSTimer 来规划时间，不能使用任意的 UI 操作

4. 点击来添加和删除时钟

5. 显示时区的名字和数码格式的时间

6. 数码时钟来显示的格式： HH:mm:ss

如何使用

1. Import the files SPClockView.h and SPClockView.m into your projects.
2. After adding the SPClockView into your parent view, set its time zone by calling setTimeZone: method.
3. Digital clock SPDigitalClock is a subclass of UILabel, and is implemented inside the SPClockView class. To set the digital time also call the method setTimeZone: on SPDigitalClock

示例：

1. SPClockView

   SPClockView *clockView = [[SPClockView alloc] initWithFrame:CGRectMake(0, 0, 140, 140)];    [clockView setTimeZone:[NSTimeZone timeZoneWithAbbreviation:@"EDT"]]; // New York

2. SPDigitalClock

   SPDigitalClock *digClock = [[SPDigitalClock alloc] initWithFrame:CGRectMake(0, 0, 140, 140)];    [digClock setTimeZone:[NSTimeZone timeZoneWithAbbreviation:@"EDT"]]; // New York

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