关于UIAlertController的基本使用:

• UIAlertControlle 弹出样式:
  UIAlertControllerStyleAlert 在屏幕中间
  UIAlertControllerStyleActionSheet 在屏幕底部
  <pre>
  UIAlertController *alert = [UIAlertController alertControllerWithTitle:@"标题" message:@"内容" preferredStyle:UIAlertControllerStyleAlert];
  <code>

• UIAlertAction 按钮样式:
  UIAlertActionStyleDefault,
  UIAlertActionStyleCancel,
  UIAlertActionStyleDestructive
  <pre>UIAlertAction **default = [UIAlertAction actionWithTitle:@"Default" style:UIAlertActionStyleDefault
  handler:^(UIAlertAction * _Nonnull action) { NSLog(@"回调"); }];

UIAlertAction *Destructive = [UIAlertAction actionWithTitle:@"Destructive" style:UIAlertActionStyleDestructive handler:nil];

UIAlertAction *Cancel = [UIAlertAction actionWithTitle:@"Destructive" style:UIAlertActionStyleCancel handler:nil]; <code>

• 添加UIAlertAction:
  <pre>
  [alert addAction:Default];
  [alert addAction:Destructive];
  [alert addAction:Cancel];

  // 添加TextField
  [alert addTextFieldWithConfigurationHandler:^(UITextField * _Nonnull textField) {
  }];
  // 显示
  [self presentViewController:alert animated:YES completion:nil];
  <code>