一、MessageBox的Buttons

 MessageBox.Show可以出现有按钮的对话框

例如：

DialogResult dr = MessageBox.Show("是否要继续吗？", "警告！！！", MessageBoxButtons.OKCancel);//它弹出的对话框如下图所示
if (dr == DialogResult.OK)//只有按下确定按钮才执行下面
{
label1.Text = "天气不错";
}

除此之外MessageBoxButtons还有好几种对话框

二、三级联动

三个Combobox

public Form1()// Form1的构造函数
{
InitializeComponent();

AreaDataBind(comboBox1, "0001");
AreaDataBind(comboBox2, comboBox1.SelectedValue.ToString());
AreaDataBind(comboBox3, comboBox2.SelectedValue.ToString());
}

public void AreaDataBind(ComboBox cb, string Pcode)
{
cb.DataSource = new ChinaData().Select(Pcode);//数据源
cb.DisplayMember = "AreaName";//显示值
cb.ValueMember = "AreaCode";//实际值
}

private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
{
AreaDataBind(comboBox2, comboBox1.SelectedValue.ToString());
}

private void comboBox2_SelectedIndexChanged(object sender, EventArgs e)
{
AreaDataBind(comboBox3, comboBox2.SelectedValue.ToString());
}

DateTime类型比较大小：

MessageBox的Buttons和三级联动