警告框和操作表

使用步骤：
step1：创建控制器实例，同时设定title+message，通过style来确定本次创建的是警告框还是操作表
step2：创建所需的UIAlertAction实例，同时设定按钮上的title，并且在block中设定，点击按钮后要做的事情
step3：将action添加到controller中
step4：如果创建的是警告框，则可以添加textField，操作表绝对不能添加textField
step5：使用当前控制器的presentViewController方法推出AlertController
上代码：
警告框：

//点击空白处
- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
    //1.创建AlertController
    UIAlertController *alert = [UIAlertController alertControllerWithTitle:@"title" message:@"message" preferredStyle:UIAlertControllerStyleAlert];
    
    //2.创建界面上的按钮
    UIAlertAction *actionYes = [UIAlertAction actionWithTitle:@"YES" style:UIAlertActionStyleDefault handler:^(UIAlertAction * _Nonnull action) {
        //获取在文本框中输入的用户名和密码
        NSString *name = alert.textFields[0].text;
        NSString *pwd = alert.textFields[1].text;
        NSLog(@"name=%@   pwd=%@",name,pwd);
    }];
    
    UIAlertAction *actionNo = [UIAlertAction actionWithTitle:@"NO" style:UIAlertActionStyleCancel handler:^(UIAlertAction * _Nonnull action) {
        NSLog(@"NO");
    }];
    
    //3.将按钮添加到AlertController中
    [alert addAction:actionNo];
    [alert addAction:actionYes];
    
    //4.(可选)为AlertController添加文本框
    [alert addTextFieldWithConfigurationHandler:^(UITextField * _Nonnull textField) {
        //配置添加的用户名文本框
        textField.placeholder = @"用户名";
    }];
    
    [alert addTextFieldWithConfigurationHandler:^(UITextField * _Nonnull textField) {
        //配置添加的密码文本框
        textField.textColor = [UIColor redColor];
        textField.secureTextEntry = YES;
    }];
    
    //5.显示AlertController
    [self presentViewController:alert animated:YES completion:nil];
    
}

操作表：

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
    UIAlertController *actionSheet = [UIAlertController alertControllerWithTitle:nil message:nil preferredStyle:UIAlertControllerStyleActionSheet];
    UIAlertAction *action1 = [UIAlertAction actionWithTitle:@"取消" style:UIAlertActionStyleCancel handler:nil];
    
    UIAlertAction *action2 = [UIAlertAction actionWithTitle:@"转发" style:UIAlertActionStyleDefault handler:nil];
    
    UIAlertAction *action3 = [UIAlertAction actionWithTitle:@"回复" style:UIAlertActionStyleDefault handler:nil];
    
    UIAlertAction *action4 = [UIAlertAction actionWithTitle:@"删除" style:UIAlertActionStyleDestructive handler:nil];
    
    [actionSheet addAction:action4];
    [actionSheet addAction:action2];
    [actionSheet addAction:action3];
    [actionSheet addAction:action1];
    
    [self presentViewController:actionSheet animated:YES completion:nil];
}