null的用途，感觉不到它的存在价值
请问下null的用途，我这里的null删去了会有什么问题啊，我删去感觉不到有问题， 请教大家
using System;
using System.Data;
using System.Data.SqlClient;
using System.IO;
namespace LoadImages
{
class LoadImages
{
string imageFileLocation =
@"C:\Program Files\Microsoft.NET\SDK\v2.0\QuickStart\"
+ @"aspnet\samples\monitoring\tracing\Images\";
string imageFilePrefix = "milk";
int numberImageFiles = 8;
string imageFileType = ".gif";
int maxImageSize = 10000;
SqlConnection conn = null;
SqlCommand cmd = null;
static void Main()
{
LoadImages loader = new LoadImages();
try
{
// Open connection
loader.OpenConnection();
// Create command
loader.CreateCommand();
// Create table
loader.CreateImageTable();
// Prepare insert
loader.PrepareInsertImages();
// Insert images
int i;
for (i = 1; i <= loader.numberImageFiles; i++)
{
loader.ExecuteInsertImages(i);
}
}
catch (SqlException ex)
{
Console.WriteLine(ex.ToString());
}
finally
{
loader.CloseConnection();
}
}
void OpenConnection()
{
// Create connection
conn = new SqlConnection(@"
server = .\sqlexpress;
integrated security = true;
database = tempdb
");
// Open connection
conn.Open();
}
void CloseConnection()
{
// close connection
conn.Close();
Console.WriteLine("Connection Closed.");
}
void CreateCommand()
{
cmd = new SqlCommand();
cmd.Connection = conn;
}
void ExecuteCommand(string cmdText)
{
int cmdResult;
cmd.CommandText = cmdText;
Console.WriteLine("Executing command:");
Console.WriteLine(cmd.CommandText);
cmdResult = cmd.ExecuteNonQuery();
Console.WriteLine("ExecuteNonQuery returns {0}.", cmdResult);
}
void CreateImageTable()
{
ExecuteCommand(@"
create table imagetable
(
imagefile nvarchar(20),
imagedata varbinary(max)
)
");
}
void PrepareInsertImages()
{
cmd.CommandText = @"
insert into imagetable
values (@imagefile, @imagedata)
";
cmd.Parameters.Add("@imagefile", SqlDbType.NVarChar, 20);
cmd.Parameters.Add("@imagedata", SqlDbType.Image, 1000000);
cmd.Prepare();
}
void ExecuteInsertImages(int imageFileNumber)
{
string imageFileName = null;
byte[] imageImageData = null;
imageFileName =
imageFilePrefix + imageFileNumber.ToString() + imageFileType;
imageImageData =
LoadImageFile(imageFileName, imageFileLocation, maxImageSize);
cmd.Parameters["@imagefile"].Value = imageFileName;
cmd.Parameters["@imagedata"].Value = imageImageData;
ExecuteCommand(cmd.CommandText);
}
byte[] LoadImageFile(
string fileName,
string fileLocation,
int maxImageSize
)
{
byte[] imagebytes = null;
string fullpath = fileLocation + fileName;
Console.WriteLine("Loading File:");
Console.WriteLine(fullpath);
FileStream fs = new FileStream(fullpath, FileMode.Open, FileAccess.Read);
BinaryReader br = new BinaryReader(fs);
imagebytes = br.ReadBytes(maxImageSize);
Console.WriteLine(
"Imagebytes has length {0} bytes.",
imagebytes.GetLength(0)
);
return imagebytes;
}
}
}
[解决办法]
NULL OBJECT 空对象。。
[解决办法]
[解决办法]
SqlConnection conn 定义一个变量，内存里没有分配空间，
SqlConnection conn = null 定义一个变量，已经分配了空间，像空杯子。
不写null是可以编译，不过养成良好的编程习惯，合理分配内存，不要用到的时候再找杯子，而且有利于你判断对象是否为空。
[解决办法]
看你怎么用
[解决办法]
