C#中的Dialog对话框

MessageBox.Show("用户名或者密码不能为空");
MessageBox.Show("用户名或者密码不能为空","登录提示");
MessageBox.Show("用户名或者密码不能为空","登录提示",MessageBoxButtons.OKCancel);
MessageBox.Show("用户名或者密码不能为空","登录提示",MessageBoxButtons.OKCancel,MessageBoxIcon.Exclamation);

System.Windows.Forms.OpenFileDialog dlg = new System.Windows.Forms.OpenFileDialog();
dlg.Title = "打开文件";
dlg.InitialDirectory = Environment.GetFolderPath(Environment.SpecialFolder.Templates);
dlg.Filter = "txt files (*.txt)|*.txt|All files (*.*)|*.*";
dlg.FilterIndex = 2;
dlg.RestoreDirectory = true;
if (dlg.ShowDialog() == DialogResult.OK)
{
    if (dlg.FileName != "") //如果dlg.Multiselect=true;可以是dlg.FileNames
    {
        MessageBox.Show("你选择了" + dlg.FileName);
    }
}

System.IO.Stream stream;
System.Windows.Forms.SaveFileDialog saveFileDialog1 = new System.Windows.Forms.SaveFileDialog();
saveFileDialog1.Filter = "txt files (*.txt)|*.txt|All files (*.*)|*.*";
saveFileDialog1.FilterIndex = 2;
saveFileDialog1.RestoreDirectory = true;
if (saveFileDialog1.ShowDialog() == DialogResult.OK)
{
    if ((stream = saveFileDialog1.OpenFile()) != null)
    {
        // Code to write the stream goes here.
        stream.Close();
     }
}

private void printPreviewButton_Click(object sender, EventArgs e)
{
    StreamReader streamToPrint = new StreamReader("PrintMe.Txt");
    try
    {
        PrintDocument pd = new PrintDocument(streamToPrint); //假定为默认打印机
        if (storedPageSettings != null)
        {
            pd.DefaultPageSettings = storedPageSettings;
        }
        PrintPreviewDialog dlg = new PrintPreviewDialog();
        dlg.Document = pd;
        dlg.ShowDialog();
    }
    finally
    {
        streamToPrint.Close();
    }

}

private void printButton_Click(object sender, EventArgs e)
{

    StreamReader streamToPrint = new StreamReader("PrintMe.Txt");
    try
    {
        PrintDocument pd = new PrintDocument(streamToPrint);
        PrintDialog dlg = new PrintDialog();
        dlg.Document = pd;
        DialogResult result = dlg.ShowDialog();
        if (result == DialogResult.OK)
            pd.Print();

    }
    finally
    {
        streamToPrint.Close();
    }

}

public Form1(string para)//获取参数
{
    InitializeComponent();

    this.StartPosition = FormStartPosition.CenterParent;//启动位置，父窗口中央
    this.MaximizeBox = false;
    this.MinimizeBox = false;
    this.ShowIcon = false;//不显示图标
    this.ControlBox = false;
    this.ShowInTaskbar = false;
    this.FormBorderStyle = FormBorderStyle.FixedDialog;//边框样式为固定对话框
    this.btnOK.DialogResult = DialogResult.OK;//"Enter"为OK按钮
    this.btnCancel.DialogResult = DialogResult.Cancel;//“ESC”为Cancel按钮
    this.textBox1.Text = para;
}

public string ReturnText //定义一个公共属性，供调用窗口Form1使用
{
    get { return this.textBox1.Text + "b"; }
}


private void Form1_Load(object sender, EventArgs e)
{
    if (this.Owner.Name != "Form1")//Owner为调用窗体，即调用改对话框的窗体
        MessageBox.Show("非法调用");
}


private void BtnOK_Click(object sender, EventArgs e)
{
    if (this.textBox1.Text.Trim().Length == 0)
        MessageBox.Show("无输入");
    this.textBox1.Focus();
    this.DialogResult = DialogResult.None;//阻止隐藏对话框，对话框不消失
}

Form f2 = new Form2("a");

if (f2.ShowDialog(this) == DialogResult.OK)//对应Form2中的Owner，this为给对话框窗体传值
    this.textBox1.Text = f2.ReturnText;
f2.Close();
f2.Dispose();