如何将安全UITextField文本(简单地说是一堆点)更改为(*)星号字符,如下图所示?

这应该是一个简单的.我有一个AVPlayer播放视频文件,我希望能够跳到特定的时间,但我在理解CMTime工作方式时遇到了一些麻烦.
我需要以秒为单位指定时间.例如:如果我想跳到第二个10.8我想做这样的事情:
[self.avPlayer.currentItem seekToTime:CMTimeMakeWithSeconds(10.8, 1];
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但我没有得到我想要的结果.
我有两个UIViewControllers有一个AVPlayer应该播放视频文件时,他们被推入UINavigationController:
-(void)viewWillAppear:(BOOL)animated{
videoView = [[UIView alloc]initWithFrame:self.view.frame];
NSString *filepath = [[NSBundle mainBundle] pathForResource:@"myVideo" ofType:@"mov"];
NSURL *fileURL = [NSURL fileURLWithPath:filepath];
self.avPlayer = [AVPlayer playerWithURL:fileURL];
AVPlayerLayer *foregroundLayer = [AVPlayerLayer playerLayerWithPlayer:self.avPlayer];
self.avPlayer.actionAtItemEnd = AVPlayerActionAtItemEndNone;
foregroundLayer.frame = self.view.frame;
foregroundLayer.videoGravity = AVLayerVideoGravityResizeAspectFill;
[videoView.layer addSublayer:foregroundLayer];
[self.view addSubview:videoView];
self.avPlayer.actionAtItemEnd = AVPlayerActionAtItemEndNone;
[[NSNotificationCenter defaultCenter] addObserver:self
selector:@selector(playerItemDidReachEnd:)
name:AVPlayerItemDidPlayToEndTimeNotification
object:[self.avPlayer currentItem]];
}
-(void)viewDidAppear:(BOOL)animated{
[self.avPlayer play];
}
-(void)playerItemDidReachEnd:(NSNotification *)notification {
[self.navigationController popViewControllerAnimated:NO]
}
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我第一次推动任何UIViewControllers播放效果都很好.但在那之后,如果我再推它们中的任何一个声音,但视频会冻结.
我尝试过使用MPMoviePlayerViewController但行为是一样的.有什么想法吗?