UIAlertController 在iPad上用法

UIAlertController在iPad上用法，请注意，“取消”按钮显示不了。

     UIAlertController *alert = [UIAlertController alertControllerWithTitle:nil message:nil 
       preferredStyle:UIAlertControllerStyleActionSheet];
       //加上下面的判断
    if (alert.popoverPresentationController) {
         [alert.popoverPresentationController setPermittedArrowDirections:0];//去掉arrow箭头
         alert.popoverPresentationController.sourceView = self.view;
         alert.popoverPresentationController.sourceRect = CGRectMake(0, self.view.height, self.view.width, self.view.height);
     }
    
     UIAlertAction * action1 = [UIAlertAction actionWithTitle:@"照相机" style:UIAlertActionStyleDefault handler:^(UIAlertAction * _Nonnull action) {
         
     }];
     UIAlertAction * action2 = [UIAlertAction actionWithTitle:@"相册" style:UIAlertActionStyleDefault handler:^(UIAlertAction * _Nonnull action) {

     }];
     UIAlertAction * action3 = [UIAlertAction actionWithTitle:@"取消" style:UIAlertActionStyleCancel handler:^(UIAlertAction * _Nonnull action) {
     }];
     [alert addAction:action1];
     [alert addAction:action2];
     [alert addAction:action3];
     alert.modalPresentationStyle =0;
     [self presentViewController:alert animated:YES completion:nil];

iPhone上对应用法：

     UIAlertController * alert = [UIAlertController alertControllerWithTitle:nil message:nil preferredStyle:UIAlertControllerStyleActionSheet];
     UIAlertAction * action1 = [UIAlertAction actionWithTitle:@"照相机" style:UIAlertActionStyleDefault handler:^(UIAlertAction * _Nonnull action) {

     }];
     UIAlertAction * action2 = [UIAlertAction actionWithTitle:@"相册" style:UIAlertActionStyleDefault handler:^(UIAlertAction * _Nonnull action) {

     }];
     UIAlertAction * action3 = [UIAlertAction actionWithTitle:@"取消" style:UIAlertActionStyleCancel handler:^(UIAlertAction * _Nonnull action) {
     }];
     [alert addAction:action1];
     [alert addAction:action2];
     [alert addAction:action3];
     alert.modalPresentationStyle =0;
     [self presentViewController:alert animated:YES completion:nil];