關於在DataGridView中嵌入圖片……

有一句英語名言——Picutures speak louder than words（圖片勝於千言萬語）。可見在描述一些細節問題，或者是用語言文字難以讓人產生“身臨其境”的時候，圖片就發揮了其作用。在WinForm中，DataGridView不僅僅是用於顯示文字、我們還可以顯示圖片。本章就和大伙兒討論DataGridView中嵌入顯示圖片的問題。

一、嵌入式顯示：

所謂“嵌入式”，就是說把圖片單獨存放在某個DataTable的字段中（該字段為byte[]類型）然后綁定到對應DataGridView的指定單元格中顯示出來，代碼大致如下：

[C#]

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

        public Form1()
        {
            InitializeComponent();

            //初始化動態產生數據表等字段
            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()

        '初始化動態產生數據表等字段
        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

這樣做的好處在於：由於你的圖片文件被嵌入到了數據庫中（這里是模擬數據庫的效果，真實情況下你應該使用DataAdapter.Fill填充到DataTable中方可）。這樣不存在圖片丟失等情況；當然數據庫的容量也大大增加。

二、連接式圖片顯示：

這是我給起的名字，就是類似我“關於資源文件”中那個“Link when compile"效果差不多——只在動態綁定的時候根據一定規律（如存儲在數據庫中的絕對或者相對路徑）順序加載圖片，這樣圖片和數據庫必然是分離的。不過拷貝的時候注意路徑等問題。示例代碼如下：

[C#]

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

        public Form1()
        {
            InitializeComponent();

            //初始化動態產生數據表等字段
            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()

        '初始化動態產生數據表等字段
        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

以上代碼和第一種”嵌入式“差不多，不過還請注意一下重要差別：

1）自定義了各個Columns，而不是自動生成（這是因為DataTable中都是string類型，包括存儲圖片的路徑，如果單用自動生成的話則無法生成Image類型的列）。

2）人為使用了CellFormatting事件，該事件在呈現整個DataGridView的時候被出發。此時該事件的e的RowIndex將從0~最后一行（實際在DataTable中不存在），ColumnIndex從0~最后一列逐個遍歷。如If中判斷，其中e.ColumnIndex=1表示第一列，e.RowIndex不等於dgv.NewRowIndex表示不等於最后一行。同時給e.Value（實際單元格中內容）直接賦予其byte數組即可。

附帶說明一下：你把DataGridView的AllowUserToAddRows設置為False，那么“e.RowIndex <> dgv.NewRowIndex”完全可以省略。

有興趣的話，可以嘗試結合我“關於資源文件”的方法，先把圖片嵌入到資源文件中，然后在DataTable中某列添加各個對應資源文件的相對路徑和名稱，然后動態加載。

三、圖片大小調整：

有時我們喜歡統一把圖片“按比例縮放”，不喜歡很大或者很小的圖片——怎么辦？我們可以采取把圖片的byte數組讀入一個Memory中，然后加載到Image，同時創建新的BitMap（利用其構造函數定義統一的Size），然后存儲到另外一個MemoryStream中並且使用其ToArray方法與DataGridView進行綁定。

對於“嵌入式”，示例代碼如下：

[C#]

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

        public Form1()
        {
            InitializeComponent();

            //初始化動態產生數據表等字段
            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()

        '初始化動態產生數據表等字段
        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

注意我還是沿用了CellFormatting事件，並且請觀察該事件內部代碼。如果是“連接式”的，只需更改第二列的類型，並且在CellFormatting中讀取該列存儲的圖片路徑，轉化為byte即可。
[C#]

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

        public Form1()
        {
            InitializeComponent();

            //初始化動態產生數據表等字段
            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()

        '初始化動態產生數據表等字段
        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