关于在DataGridView中嵌入图片……

有一句英语名言——Picutures speak louder than words（图片胜于千言万语）。可见在描述一些细节问题，或者是用语言文字难以让人产生“身临其境”的时候，图片就发挥了其作用。在WinForm中，DataGridView不仅仅是用于显示文字、我们还可以显示图片。本章就和大伙儿讨论DataGridView中嵌入显示图片的问题。

一、嵌入式显示：

所谓“嵌入式”，就是说把图片单独存放在某个DataTable的字段中（该字段为byte[]类型）然后绑定到对应DataGridView的指定单元格中显示出来，代码大致如下：

[C#]

public partial class Form1 : Form
    {
        DataGridView dgv = null;

        public Form1()
        {
            InitializeComponent();

            //初始化动态产生数据表等字段
            dgv = new DataGridView();
            dgv.Parent = this;
            dgv.Dock = DockStyle.Fill;

            DataTable dt = new DataTable();
            dt.Columns.Add("Name", typeof(string));
            dt.Columns.Add("Image", typeof(byte[]));
            dt.Rows.Add("Test1", File.ReadAllBytes("d:\\test.jpg"));
            dgv.AutoSizeColumnsMode = DataGridViewAutoSizeColumnsMode.AllCells;
            dgv.AutoSizeRowsMode = DataGridViewAutoSizeRowsMode.AllCells;
            dgv.DataSource = dt;
        }
    }

[VB.NET]

Public Partial Class Form1
    Inherits Form
    Private dgv As DataGridView = Nothing

    Public Sub New()
        InitializeComponent()

        '初始化动态产生数据表等字段
        dgv = New DataGridView()
        dgv.Parent = Me
        dgv.Dock = DockStyle.Fill

        Dim dt As New DataTable()
        dt.Columns.Add("Name", GetType(String))
        dt.Columns.Add("Image", GetType(Byte()))
        dt.Rows.Add("Test1", File.ReadAllBytes("d:\test.jpg"))
        dgv.AutoSizeColumnsMode = DataGridViewAutoSizeColumnsMode.AllCells
        dgv.AutoSizeRowsMode = DataGridViewAutoSizeRowsMode.AllCells
        dgv.DataSource = dt
    End Sub
End Class

这样做的好处在于：由于你的图片文件被嵌入到了数据库中（这里是模拟数据库的效果，真实情况下你应该使用DataAdapter.Fill填充到DataTable中方可）。这样不存在图片丢失等情况；当然数据库的容量也大大增加。

二、连接式图片显示：

这是我给起的名字，就是类似我“关于资源文件”中那个“Link when compile"效果差不多——只在动态绑定的时候根据一定规律（如存储在数据库中的绝对或者相对路径）顺序加载图片，这样图片和数据库必然是分离的。不过拷贝的时候注意路径等问题。示例代码如下：

[C#]

public partial class Form1 : Form
    {
        DataGridView dgv = null;

        public Form1()
        {
            InitializeComponent();

            //初始化动态产生数据表等字段
            dgv = new DataGridView();
            dgv.Parent = this;
            dgv.Dock = DockStyle.Fill;

            DataTable dt = new DataTable();
            dt.Columns.Add("Name", typeof(string));
            dt.Columns.Add("Image", typeof(string));
            dt.Rows.Add("Test1", "d:\\test.jpg");
            dgv.AutoSizeColumnsMode = DataGridViewAutoSizeColumnsMode.AllCells;
            dgv.AutoSizeRowsMode = DataGridViewAutoSizeRowsMode.AllCells;
            dgv.Columns.Add(new DataGridViewTextBoxColumn() { HeaderText = "Name", DataPropertyName = "Name" });
            dgv.Columns.Add(new DataGridViewImageColumn() { HeaderText = "Image", DataPropertyName = "Image" });
            dgv.CellFormatting += new DataGridViewCellFormattingEventHandler(dgv_CellFormatting);
            dgv.DataSource = dt;
        }

        void dgv_CellFormatting(object sender, DataGridViewCellFormattingEventArgs e)
        {
            if (e.ColumnIndex==1 && e.RowIndex!=dgv.NewRowIndex)
            {
                e.Value = File.ReadAllBytes(dgv.Rows[e.RowIndex].Cells[1].Value.ToString());
            }
        }
    }

[VB.NET]

Public Partial Class Form1
    Inherits Form
    Private dgv As DataGridView = Nothing

    Public Sub New()
        InitializeComponent()

        '初始化动态产生数据表等字段
        dgv = New DataGridView()
        dgv.Parent = Me
        dgv.Dock = DockStyle.Fill

        Dim dt As New DataTable()
        dt.Columns.Add("Name", GetType(String))
        dt.Columns.Add("Image", GetType(String))
        dt.Rows.Add("Test1", "d:\test.jpg")
        dgv.AutoSizeColumnsMode = DataGridViewAutoSizeColumnsMode.AllCells
        dgv.AutoSizeRowsMode = DataGridViewAutoSizeRowsMode.AllCells
        dgv.Columns.Add(New DataGridViewTextBoxColumn() With { _
            Key .HeaderText = "Name", _
            Key .DataPropertyName = "Name" _
        })
        dgv.Columns.Add(New DataGridViewImageColumn() With { _
            Key .HeaderText = "Image", _
            Key .DataPropertyName = "Image" _
        })
        AddHandler dgv.CellFormatting, AddressOf New DataGridViewCellFormattingEventHandler(AddressOf dgv_CellFormatting)
        dgv.DataSource = dt
    End Sub

    Private Sub dgv_CellFormatting(sender As Object, e As DataGridViewCellFormattingEventArgs)
        If e.ColumnIndex = 1 AndAlso e.RowIndex <> dgv.NewRowIndex Then
            e.Value = File.ReadAllBytes(dgv.Rows(e.RowIndex).Cells(1).Value.ToString())
        End If
    End Sub
End Class

以上代码和第一种”嵌入式“差不多，不过还请注意一下重要差别：

1）自定义了各个Columns，而不是自动生成（这是因为DataTable中都是string类型，包括存储图片的路径，如果单用自动生成的话则无法生成Image类型的列）。

2）人为使用了CellFormatting事件，该事件在呈现整个DataGridView的时候被出发。此时该事件的e的RowIndex将从0~最后一行（实际在DataTable中不存在），ColumnIndex从0~最后一列逐个遍历。如If中判断，其中e.ColumnIndex=1表示第一列，e.RowIndex不等于dgv.NewRowIndex表示不等于最后一行。同时给e.Value（实际单元格中内容）直接赋予其byte数组即可。

附带说明一下：你把DataGridView的AllowUserToAddRows设置为False，那么“e.RowIndex <> dgv.NewRowIndex”完全可以省略。

有兴趣的话，可以尝试结合我“关于资源文件”的方法，先把图片嵌入到资源文件中，然后在DataTable中某列添加各个对应资源文件的相对路径和名称，然后动态加载。

三、图片大小调整：

有时我们喜欢统一把图片“按比例缩放”，不喜欢很大或者很小的图片——怎么办？我们可以采取把图片的byte数组读入一个Memory中，然后加载到Image，同时创建新的BitMap（利用其构造函数定义统一的Size），然后存储到另外一个MemoryStream中并且使用其ToArray方法与DataGridView进行绑定。

对于“嵌入式”，示例代码如下：

[C#]

 public partial class Form1 : Form
    {
        DataGridView dgv = null;

        public Form1()
        {
            InitializeComponent();

            //初始化动态产生数据表等字段
            dgv = new DataGridView();
            dgv.Parent = this;
            dgv.Dock = DockStyle.Fill;

            DataTable dt = new DataTable();
            dt.Columns.Add("Name", typeof(string));
            dt.Columns.Add("Image", typeof(byte[]));
            dt.Rows.Add("Test1", File.ReadAllBytes("d:\\test.jpg"));
            dgv.AutoSizeColumnsMode = DataGridViewAutoSizeColumnsMode.AllCells;
            dgv.AutoSizeRowsMode = DataGridViewAutoSizeRowsMode.AllCells;
            dgv.CellFormatting += new DataGridViewCellFormattingEventHandler(dgv_CellFormatting);
            dgv.AllowUserToAddRows = false;
            dgv.DataSource = dt;
        }

        void dgv_CellFormatting(object sender, DataGridViewCellFormattingEventArgs e)
        {
            if (e.ColumnIndex == 1)
            {
                using (MemoryStream oldms = new MemoryStream((byte[])e.Value))
                {
                    Image img = Image.FromStream(oldms);
                    Bitmap bt = new Bitmap(img,new Size(100, 100));
                    using (MemoryStream newms = new MemoryStream())
                    {
                        bt.Save(newms,ImageFormat.Jpeg);
                        e.Value = newms.ToArray();
                    }
                }
            }
        }
    }

[VB.NET]

Public Partial Class Form1
    Inherits Form
    Private dgv As DataGridView = Nothing

    Public Sub New()
        InitializeComponent()

        '初始化动态产生数据表等字段
        dgv = New DataGridView()
        dgv.Parent = Me
        dgv.Dock = DockStyle.Fill

        Dim dt As New DataTable()
        dt.Columns.Add("Name", GetType(String))
        dt.Columns.Add("Image", GetType(Byte()))
        dt.Rows.Add("Test1", File.ReadAllBytes("d:\test.jpg"))
        dgv.AutoSizeColumnsMode = DataGridViewAutoSizeColumnsMode.AllCells
        dgv.AutoSizeRowsMode = DataGridViewAutoSizeRowsMode.AllCells
        AddHandler dgv.CellFormatting,AddressOf New DataGridViewCellFormattingEventHandler(AddressOf dgv_CellFormatting)
        dgv.AllowUserToAddRows = False
        dgv.DataSource = dt
    End Sub

    Private Sub dgv_CellFormatting(sender As Object, e As DataGridViewCellFormattingEventArgs)
        If e.ColumnIndex = 1 Then
            Using oldms As New MemoryStream(DirectCast(e.Value, Byte()))
                Dim img As Image = Image.FromStream(oldms)
                Dim bt As New Bitmap(img, New Size(100, 100))
                Using newms As New MemoryStream()
                    bt.Save(newms, ImageFormat.Jpeg)
                    e.Value = newms.ToArray()
                End Using
            End Using
        End If
    End Sub
End Class

注意我还是沿用了CellFormatting事件，并且请观察该事件内部代码。如果是“连接式”的，只需更改第二列的类型，并且在CellFormatting中读取该列存储的图片路径，转化为byte即可。
[C#]

 public partial class Form1 : Form
    {
        DataGridView dgv = null;

        public Form1()
        {
            InitializeComponent();

            //初始化动态产生数据表等字段
            dgv = new DataGridView();
            dgv.Parent = this;
            dgv.Dock = DockStyle.Fill;

            DataTable dt = new DataTable();
            dt.Columns.Add("Name", typeof(string));
            dt.Columns.Add("Image", typeof(string));
            dt.Rows.Add("Test1", "d:\\test.jpg");
            dgv.AutoSizeColumnsMode = DataGridViewAutoSizeColumnsMode.AllCells;
            dgv.AutoSizeRowsMode = DataGridViewAutoSizeRowsMode.AllCells;

            dgv.Columns.Add(new DataGridViewTextBoxColumn() { HeaderText = "Name", DataPropertyName = "Name" });
            dgv.Columns.Add(new DataGridViewImageColumn() { HeaderText = "Image", DataPropertyName = "Image" });
            dgv.CellFormatting += new DataGridViewCellFormattingEventHandler(dgv_CellFormatting);
            dgv.AllowUserToAddRows = false;
            dgv.DataSource = dt;
        }

        void dgv_CellFormatting(object sender, DataGridViewCellFormattingEventArgs e)
        {
            if (e.ColumnIndex == 1)
            {
                byte[] bytes = File.ReadAllBytes(e.Value.ToString());
                using (MemoryStream oldms = new MemoryStream(bytes))
                {
                    Image img = Image.FromStream(oldms);
                    Bitmap bt = new Bitmap(img,new Size(100, 100));
                    using (MemoryStream newms = new MemoryStream())
                    {
                        bt.Save(newms,ImageFormat.Jpeg);
                        e.Value = newms.ToArray();
                    }
                }
            }
        }
    }

[VB.NET]

Public Partial Class Form1
    Inherits Form
    Private dgv As DataGridView = Nothing

    Public Sub New()
        InitializeComponent()

        '初始化动态产生数据表等字段
        dgv = New DataGridView()
        dgv.Parent = Me
        dgv.Dock = DockStyle.Fill

        Dim dt As New DataTable()
        dt.Columns.Add("Name", GetType(String))
        dt.Columns.Add("Image", GetType(String))
        dt.Rows.Add("Test1", "d:\test.jpg")
        dgv.AutoSizeColumnsMode = DataGridViewAutoSizeColumnsMode.AllCells
        dgv.AutoSizeRowsMode = DataGridViewAutoSizeRowsMode.AllCells

        dgv.Columns.Add(New DataGridViewTextBoxColumn() With { _
            Key .HeaderText = "Name", _
            Key .DataPropertyName = "Name" _
        })
        dgv.Columns.Add(New DataGridViewImageColumn() With { _
            Key .HeaderText = "Image", _
            Key .DataPropertyName = "Image" _
        })
        AddHandler dgv.CellFormatting,AddressOf New DataGridViewCellFormattingEventHandler(AddressOf dgv_CellFormatting)
        dgv.AllowUserToAddRows = False
        dgv.DataSource = dt
    End Sub

    Private Sub dgv_CellFormatting(sender As Object, e As DataGridViewCellFormattingEventArgs)
        If e.ColumnIndex = 1 Then
            Dim bytes As Byte() = File.ReadAllBytes(e.Value.ToString())
            Using oldms As New MemoryStream(bytes)
                Dim img As Image = Image.FromStream(oldms)
                Dim bt As New Bitmap(img, New Size(100, 100))
                Using newms As New MemoryStream()
                    bt.Save(newms, ImageFormat.Jpeg)
                    e.Value = newms.ToArray()
                End Using
            End Using
        End If
    End Sub
End Class