想想我们身边的一些例子，当你设置你的QQ头像后，再次登录你的头像就是上次你设置并保存的那个图片。那头像是存放在哪里了呢？存放方式有很多种，我们选择比较合适的方式就行。下面介绍一下我们系统使用的一种方法 。

一、需求

         给粮库加载一张背景图片，并下次加载时显示出来。其实和保存QQ头像是一样的原理。

二、解决方案

  1、将图片存放在数据库中

步骤：

1.    在数据库中建立一张表，将存储的图片的字段类型设为Image类型
   
2.    用FileStream类、BinaryReader把图片读成字节的形式，赋给一个字节数组
   
3.    用ADO.SqlCommand对象的ExecuteNonQuery()方法把数据保存到数据库

实例：

U层

   Private Sub FrmHouseLayoutSet_FormClosed(sender As Object, e As FormClosedEventArgs) Handles
   Me.FormClosed

        Dim storageBLL As New SetStorageBLL

        Dim image As New DataTable


        Try

            ‘如果openFileDialog中无图片

            If OpenFileDialog1.FileName Is Nothing Then

                Exit Sub

            Else ‘有图片

 

                ‘将图片路径给fullpath，filename获取选定图片的文件名的字符串

                Dim fullpath As String = OpenFileDialog1.FileName

 

                ‘使用指定的路径、创建模式、读/写权限和共享权限创建 FileStream 类的新实例

                Dim fs As FileStream = New FileStream(fullpath, FileMode.Open, FileAccess.Read, 
                FileShare.Read)

                ‘length获取用字节表示的流长度

                Dim imagebytes() As Byte = New Byte(fs.Length) {}

                ‘BinaryReader用特定的编码将基元数据类型读作二进制值

                Dim br As BinaryReader = New BinaryReader(fs)

 

                ‘从当前流中读取指定的字节数以写入字节数组中，并将当前位置前移相应的字节数

                imagebytes = br.ReadBytes(Convert.ToInt32(fs.Length))

 

                ‘保存图片

                If storageBLL.SaveBackImage(imagebytes) = True Then  ‘保存成功退出

                    Exit Sub

                Else ‘失败弹出对话框

                    MsgBox("背景图片保存失败！", vbOKOnly, "信息提示！")

                    Exit Sub

                End If

            End If

        Catch ex As Exception

            MsgBox(ex.Message, MsgBoxStyle.OkOnly, "信息提示！")

        End Try

 

    End Sub

B层

   ‘‘‘ <summary>

    ‘‘‘ 保存背景图片

    ‘‘‘ </summary>

    ‘‘‘ <param name="byImage">图片的二进制形式</param>

    ‘‘‘ <returns>是否保存成功， 成功返回true 否则返回false</returns>

    ‘‘‘ <remarks>高晓青  2013-11-22</remarks>

    Public Function SaveBackImage(ByVal byImage As Byte()) As Boolean

        Dim iStorage As IStorageDevice

 

        iStorage = factory.CreateStorageDevice

 

        Return iStorage.SaveBackImage(byImage)

    End Function

工厂层

    ‘‘‘ <summary>

    ‘‘‘ 仓房内设备

    ‘‘‘ </summary>

    Public Function CreateStorageDevice() As IStorageDevice

 

        Dim className As String ‘定义实例化类的名称 

        Dim storageDevice As IStorageDevice ‘定义类的返回类型 

 

        className = AssemblyName + "." + db + "StorageDeviceDAL"‘为实例化类名称赋值，程序集名称+类名 

        storageDevice = CType(Assembly.Load(AssemblyName).CreateInstance(className), IStorageDevice)    

 

        Return storageDevice ‘返回值 

    End Function

 

接口层

   ‘‘‘ <summary>

    ‘‘‘ 保存背景图片

    ‘‘‘ </summary>

    ‘‘‘ <param name="byImage">图片的二进制形式</param>

    ‘‘‘ <returns>是否保存成功， 成功返回true 否则返回false</returns>

    ‘‘‘ <remarks>高晓青  2013-11-22</remarks>

    Function SaveBackImage(ByVal byImage As Byte()) As Boolean

D层

    ‘‘‘ <summary>

    ‘‘‘ 保存背景图片

    ‘‘‘ </summary>

    ‘‘‘ <param name="byImage">图片的二进制形式</param>

    ‘‘‘ <returns>是否保存成功， 成功返回true 否则返回false</returns>

    ‘‘‘ <remarks>高晓青  2013-11-22</remarks>

    Public Function SaveBackImage(byImage As Byte()) As Boolean Implements IStorageDevice.SaveBackImage

 

        Dim strSql As String = "if  not exists(select *  from T_SaveBackImage )   insert into " & _
        "T_SaveBackImage(backImage)values(@BackImage) else update T_SaveBackImage set " & _
        "backImage=@BackImage"

        Dim helper As New SqlHelper

        Dim sqlParamers As SqlParameter() = {New SqlParameter("@BackImage", byImage)}

        Dim bolInsert = helper.UpdDelAlter(strSql, CommandType.Text, sqlParamers)

        Return bolInsert

    End Function

2、将图片从数据库中读取

步骤：

1. 利用SqlDataReader从数据库中把Image字段值读出来，赋给一个Byte()字节数组
2. 使用MemoryStream类与Bitmap把图片读取出来

实例：

U层

           ‘读取背景图片,定义byte数组类型的变量imagebytes

            Dim imagebytes As Byte()

            ‘从数据库中读取图片

            imagebytes = storageBLL.GetImage()

            ‘创建其支持存储区为内存的流,MemoryStream(imagebytes)基于指定的字节数组初始化 MemoryStream 
             类的无法调整大小的新实例

            Dim ms As MemoryStream = New MemoryStream(imagebytes)

            ‘Bitmap 是用于处理由像素数据定义的图像的对象,Bitmap(ms)从指定的数据流初始化 
            Bitmap 类的新实例

            Dim bmpt As Bitmap = New Bitmap(ms)

 

            ‘将数据库中的图片赋值给控件

            plLocation.BackgroundImage = bmpt

 

B层

    ‘‘‘ <summary>

    ‘‘‘ 查询背景图片

    ‘‘‘ </summary>

    ‘‘‘ <returns>背景图片的二进制保存形式</returns>

    ‘‘‘ <remarks></remarks>

    Public Function GetImage() As Byte()

        Dim iStorage As IStorageDevice

 

        iStorage = factory.CreateStorageDevice

 

        Return iStorage.GetImage()

    End Function

 

 

工厂层

 ‘‘‘ <summary>

    ‘‘‘ 仓房内设备

    ‘‘‘ </summary>

    Public Function CreateStorageDevice() As IStorageDevice

 

        Dim className As String ‘定义实例化类的名称 

        Dim storageDevice As IStorageDevice ‘定义类的返回类型 

 

 className = AssemblyName + "." + db + "StorageDeviceDAL"    ‘为实例化类名称赋值，程序集名称+类名 

 storageDevice = CType(Assembly.Load(AssemblyName).CreateInstance(className), IStorageDevice)  

 

        Return storageDevice ‘返回值 

    End Function

 

接口层

 

    ‘‘‘ <summary>

    ‘‘‘ 查询背景图片

    ‘‘‘ </summary>

    ‘‘‘ <returns>背景图片的二进制保存形式</returns>

    ‘‘‘ <remarks>高晓青  2013-11-22</remarks>

    Function GetImage() As Byte()

 

D层

  ‘‘‘ <summary>

    ‘‘‘ 查询背景图片

    ‘‘‘ </summary>

    ‘‘‘ <returns>背景图片的二进制保存形式</returns>

    ‘‘‘ <remarks>高晓青  2013-11-22</remarks>

    Public Function GetImage() As Byte() Implements IStorageDevice.GetImage

        Dim strSql As String = "select backImage from T_SaveBackImage"

 

        Dim helper As New SqlHelper

        Dim bolInsert = helper.GetImage(strSql, CommandType.Text)

 

        Return bolInsert

    End Function