C# DataColumn.AllowDBNull属性代码示例

private void AddNullAllowedColumn()
{
    DataColumn column;
    column = new DataColumn("classID", 
        System.Type.GetType("System.Int32"));
    column.AllowDBNull = true;

    // Add the column to a new DataTable.
    DataTable table;
    table = new DataTable();
    table.Columns.Add(column);
}

//引入命名空间
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;

public class Car {
    public string carPetName, carMake, carColor;
    public Car(string petName, string make, string color) {
        carPetName = petName;
        carColor = color;
        carMake = make;
    }
}
public class MainForm : Form {
    private List<Car> arTheCars = new List<Car>();
    private DataTable inventoryTable = new DataTable("Inventory");
    DataView coltsOnlyView;      // I only show red colts.

    public MainForm() {
        InitializeComponent();
        arTheCars.Add(new Car("C", "BMW", "Green"));
        arTheCars.Add(new Car("T", "Y", "White"));
        arTheCars.Add(new Car("AAA", "Jeep", "Tan"));
        arTheCars.Add(new Car("PInducer", "Caravan", "Pink"));
        arTheCars.Add(new Car("F", "BMW", "Pea Soup Green"));
        arTheCars.Add(new Car("B", "BMW", "Black"));
        arTheCars.Add(new Car("M", "DDD", "Red"));
        arTheCars.Add(new Car("S", "Colt", "Black"));

        CreateDataTable();
        CreateDataView();
    }

    private void CreateDataTable() {
        DataColumn carIDColumn = new DataColumn("CarID", typeof(int));
        carIDColumn.ReadOnly = true;
        carIDColumn.Caption = "Car ID";
        carIDColumn.AllowDBNull = false;
        carIDColumn.Unique = true;
        carIDColumn.AutoIncrement = true;
        carIDColumn.AutoIncrementSeed = 0;
        carIDColumn.AutoIncrementStep = 1;
        carIDColumn.ColumnMapping = MappingType.Attribute;

        DataColumn carMakeColumn = new DataColumn("Make", typeof(string));
        DataColumn carColorColumn = new DataColumn("Color", typeof(string));
        DataColumn carPetNameColumn = new DataColumn("PetName", typeof(string));
        carPetNameColumn.Caption = "Pet Name";
        inventoryTable.Columns.AddRange(new DataColumn[] { carIDColumn, carMakeColumn, carColorColumn, carPetNameColumn });

        inventoryTable.PrimaryKey = new DataColumn[] { inventoryTable.Columns[0] };

        foreach (Car c in arTheCars) {
            DataRow newRow = inventoryTable.NewRow();
            newRow["Make"] = c.carMake;
            newRow["Color"] = c.carColor;
            newRow["PetName"] = c.carPetName;
            inventoryTable.Rows.Add(newRow);
        }
        carInventoryGridView.DataSource = inventoryTable;
    }
    private void CreateDataView() {
        coltsOnlyView = new DataView(inventoryTable);
        coltsOnlyView.RowFilter = "Make = 'Colt'";
        dataGridColtsView.DataSource = coltsOnlyView;
    }
    private void btnRemoveRow_Click(object sender, EventArgs e) {
        try {
            inventoryTable.Rows[(int.Parse(txtRowToRemove.Text))].Delete();
            inventoryTable.AcceptChanges();
        } catch (Exception ex) {
            MessageBox.Show(ex.Message);
        }
    }

    private void btnGetMakes_Click(object sender, EventArgs e) {
        string filterStr = string.Format("Make= '{0}' ", txtMakeToGet.Text);
        DataRow[] makes = inventoryTable.Select(filterStr, "PetName DESC");
        if (makes.Length == 0)
            MessageBox.Show("Sorry, no cars...", "Selection error!");
        else {
            string strMake = null;
            for (int i = 0; i < makes.Length; i++) {
                DataRow temp = makes[i];
                strMake += temp["PetName"] + "\n";
            }
            MessageBox.Show(strMake, txtMakeToGet.Text + " type(s):");
        }
    }

    private void btnChangeBeemersToColts_Click(object sender, EventArgs e) {
        string filterStr = "Make='BMW'";
        string strMake = null;

        DataRow[] makes = inventoryTable.Select(filterStr);
        for (int i = 0; i < makes.Length; i++) {
            DataRow temp = makes[i];
            strMake += temp["Make"] = "Colt";
            makes[i] = temp;
        }
    }
    private void ShowCarsWithIdLessThanFive() {
        DataRow[] properIDs;
        string newFilterStr = "ID > '5'";
        properIDs = inventoryTable.Select(newFilterStr);
        string strIDs = null;
        for (int i = 0; i < properIDs.Length; i++) {
            DataRow temp = properIDs[i];
            strIDs += temp["PetName"]
                + " is ID " + temp["ID"] + "\n";
        }
        MessageBox.Show(strIDs, "Pet names of cars where ID > 5");
    }
    private void InitializeComponent() {
        this.label1 = new System.Windows.Forms.Label();
        this.carInventoryGridView = new System.Windows.Forms.DataGridView();
        this.btnRemoveRow = new System.Windows.Forms.Button();
        this.txtRowToRemove = new System.Windows.Forms.TextBox();
        this.txtMakeToGet = new System.Windows.Forms.TextBox();
        this.btnGetMakes = new System.Windows.Forms.Button();
        this.btnChangeBeemersToColts = new System.Windows.Forms.Button();
        this.dataGridColtsView = new System.Windows.Forms.DataGridView();
        this.label2 = new System.Windows.Forms.Label();
        ((System.ComponentModel.ISupportInitialize)(this.carInventoryGridView)).BeginInit();
        ((System.ComponentModel.ISupportInitialize)(this.dataGridColtsView)).BeginInit();
        this.SuspendLayout();
        // 
        this.label1.AutoSize = true;
        this.label1.Location = new System.Drawing.Point(11, 76);
        this.label1.Name = "label1";
        this.label1.Size = new System.Drawing.Size(102, 13);
        this.label1.TabIndex = 0;
        this.label1.Text = "All Cars in DataTable";
        // 
        this.carInventoryGridView.Location = new System.Drawing.Point(12, 93);
        this.carInventoryGridView.Name = "carInventoryGridView";
        this.carInventoryGridView.Size = new System.Drawing.Size(392, 150);
        this.carInventoryGridView.TabIndex = 1;
        this.carInventoryGridView.Text = "dataGridView1";
        // 
        this.btnRemoveRow.Location = new System.Drawing.Point(12, 13);
        this.btnRemoveRow.Name = "btnRemoveRow";
        this.btnRemoveRow.Size = new System.Drawing.Size(101, 23);
        this.btnRemoveRow.TabIndex = 2;
        this.btnRemoveRow.Text = "Remove Row #";
        this.btnRemoveRow.Click += new System.EventHandler(this.btnRemoveRow_Click);
        // 
        this.txtRowToRemove.Location = new System.Drawing.Point(120, 15);
        this.txtRowToRemove.Name = "txtRowToRemove";
        this.txtRowToRemove.Size = new System.Drawing.Size(100, 20);
        this.txtRowToRemove.TabIndex = 3;
        // 
        this.txtMakeToGet.Location = new System.Drawing.Point(120, 44);
        this.txtMakeToGet.Name = "txtMakeToGet";
        this.txtMakeToGet.Size = new System.Drawing.Size(100, 20);
        this.txtMakeToGet.TabIndex = 5;
        // 
        // btnGetMakes
        // 
        this.btnGetMakes.Location = new System.Drawing.Point(12, 42);
        this.btnGetMakes.Name = "btnGetMakes";
        this.btnGetMakes.Size = new System.Drawing.Size(101, 23);
        this.btnGetMakes.TabIndex = 4;
        this.btnGetMakes.Text = "Get These Makes";
        this.btnGetMakes.Click += new System.EventHandler(this.btnGetMakes_Click);
        // 
        // btnChangeBeemersToColts
        // 
        this.btnChangeBeemersToColts.Location = new System.Drawing.Point(245, 15);
        this.btnChangeBeemersToColts.Name = "btnChangeBeemersToColts";
        this.btnChangeBeemersToColts.Size = new System.Drawing.Size(159, 23);
        this.btnChangeBeemersToColts.TabIndex = 6;
        this.btnChangeBeemersToColts.Text = "Change BMW to Colts";
        this.btnChangeBeemersToColts.Click += new System.EventHandler(this.btnChangeBeemersToColts_Click);
        // 
        // dataGridColtsView
        // 
        this.dataGridColtsView.Location = new System.Drawing.Point(12, 266);
        this.dataGridColtsView.Name = "dataGridColtsView";
        this.dataGridColtsView.Size = new System.Drawing.Size(392, 150);
        this.dataGridColtsView.TabIndex = 8;
        this.dataGridColtsView.Text = "dataGridView1";
        // 
        // label2
        // 
        this.label2.AutoSize = true;
        this.label2.Location = new System.Drawing.Point(11, 249);
        this.label2.Name = "label2";
        this.label2.Size = new System.Drawing.Size(76, 13);
        this.label2.TabIndex = 7;
        this.label2.Text = "Colts Only View";
        // 
        // MainForm
        // 
        this.AutoScaleDimensions = new System.Drawing.SizeF(6F, 13F);
        this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;
        this.ClientSize = new System.Drawing.Size(417, 433);
        this.Controls.Add(this.dataGridColtsView);
        this.Controls.Add(this.label2);
        this.Controls.Add(this.btnChangeBeemersToColts);
        this.Controls.Add(this.txtMakeToGet);
        this.Controls.Add(this.btnGetMakes);
        this.Controls.Add(this.txtRowToRemove);
        this.Controls.Add(this.btnRemoveRow);
        this.Controls.Add(this.carInventoryGridView);
        this.Controls.Add(this.label1);
        this.Name = "MainForm";
        this.Text = "Car Data Table";
        ((System.ComponentModel.ISupportInitialize)(this.carInventoryGridView)).EndInit();
        ((System.ComponentModel.ISupportInitialize)(this.dataGridColtsView)).EndInit();
        this.ResumeLayout(false);
        this.PerformLayout();
    }
    private System.Windows.Forms.Label label1;
    private System.Windows.Forms.DataGridView carInventoryGridView;
    private System.Windows.Forms.Button btnRemoveRow;
    private System.Windows.Forms.TextBox txtRowToRemove;
    private System.Windows.Forms.TextBox txtMakeToGet;
    private System.Windows.Forms.Button btnGetMakes;
    private System.Windows.Forms.Button btnChangeBeemersToColts;
    private System.Windows.Forms.DataGridView dataGridColtsView;
    private System.Windows.Forms.Label label2;

    [STAThread]
    static void Main() {
        Application.EnableVisualStyles();
        Application.Run(new MainForm());
    }
}