目前大部分电视都是16:9的显示屏，史诗级大屁股显示屏已经很少见了。iPad的屏幕是4:3的，当用iPad连接电视后，因为比例不一样，电视屏幕左右两侧会有黑边，看视频的话相当不爽。有人说用遥控器设置，公司电脑全部是海信，我找遍了菜单里所有的选项也没能去掉黑边满屏显示，所以只能从代码上下手了。
下面三个监听可以监控外接显示屏的连接情况
[[NSNotificationCenter defaultCenter] addObserver: self selector: @selector(screenDidConnectNotification:) name: UIScreenDidConnectNotification object: nil];
[[NSNotificationCenter defaultCenter] addObserver: self selector: @selector(screenDidDisconnectNotification:) name: UIScreenDidDisconnectNotification object: nil];
[[NSNotificationCenter defaultCenter] addObserver: self selector: @selector(screenModeDidChangeNotification:) name: UIScreenModeDidChangeNotification object: nil];
可以用下面的方法找到外接屏
//[UIScreen screens] 返回一个数组，包含本机和外连的所有screen，数组中第一个对象肯定是 [UIScreen mainScreen]
UIScreen *external = [[UIScreen screens] objectAtIndex: 1];//external就是电视的screen
屏幕模式，也就是屏幕的大小和像素
UIScreenMode *preferedMode = external.preferredMode;//最合适电视的屏幕模式
UIScreenMode *maxScreenMode = nil;//电视支持的最大的屏幕模式
for(int i = 0; i < [[external availableModes] count]; i++) {
UIScreenMode *current = [[[[UIScreen screens] objectAtIndex:1] availableModes] objectAtIndex: i];
if (current.size.width > max.width) {
max = current.size;
maxScreenMode = current;
}
}
external.currentMode = maxScreenMode;
//我测试的preferedMode和maxScreenMode一直是相同的，为保险还是用的maxScreenMode
屏幕的过扫描补偿(UIScreenOverscanCompensation)
typedef NS_ENUM(NSInteger, UIScreenOverscanCompensation) {
UIScreenOverscanCompensationScale, // the final composited framebuffer for the screen is scaled to avoid clipping
UIScreenOverscanCompensationInsetBounds, // the screen's bounds will be inset in the framebuffer to avoid clipping. no scaling will occur
UIScreenOverscanCompensationNone NS_ENUM_AVAILABLE_IOS(9_0), // no scaling will occur. use overscanCompensationInsets to determine the necessary insets to avoid clipping
UIScreenOverscanCompensationInsetApplicationFrame NS_ENUM_DEPRECATED_IOS(5_0, 9_0, "Use UIScreenOverscanCompensationNone") = 2,
};
//只有电视屏幕是过扫描时才有效果
external.overscanCompensation = UIScreenOverscanCompensationScale;
把iPad屏幕上的内容处理成全屏并传输到电视
大体思路就是实时截屏给external显示，上次写到这就给忘了，过了很久了就不往下写了，有需要的小伙伴可以联系我。
