btn.currentTitle
判断字符串是否为空
str.length == 0
隐藏button
btn.hidden = YES;
延迟执行
[self performSelector:@selector() withObject:nil afterDelay:1.5];
UITextField笔记
UITextField *textField = [[UITextField alloc] init];
textField.delegate = self;
//响应键盘
[textField becomeFirstResponder];
//取消响应键盘
[textField resignFirstResponder];
//
[self.view endEditing:YES];
ImageView自适应图像大小
[self.imageView sizeTofit:image];
