在petshop4.0中有这样一段代码:
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Code
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public IList<CategoryInfo> GetCategories()
{
2![](/Images/OutliningIndicators/InBlock.gif)
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IList<CategoryInfo> categories = new List<CategoryInfo>();
4![](/Images/OutliningIndicators/InBlock.gif)
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//Execute a query to read the categories
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using(SqlDataReader rdr = SqlHelper.ExecuteReader(SqlHelper.ConnectionStringLocalTransaction, CommandType.Text, SQL_SELECT_CATEGORIES, null))
{
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while (rdr.Read())
{
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CategoryInfo cat = new CategoryInfo(rdr.GetString(0), rdr.GetString(1), rdr.GetString(2));
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categories.Add(cat);
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}
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}
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return categories;
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}
在第6行处用到了using,这里我想提醒自己的是,这是using的一种用法之一。
using共有三种用法:
1.引用命名空间,减少冗余代码。
Using System.Web.UI.WebControls;
2.创建命名空间的别名(using 别名)。
using MyAlias = MyCompany.Proj.Nested;
3.即时释放资源。
Using (TestObject a = new TestObject())
{
// 使用对象
}
//对象资源被释放
上面代码其实等同于:
![](/Images/OutliningIndicators/ContractedBlock.gif)
Code
1![](/Images/OutliningIndicators/ExpandedBlockStart.gif)
try
{
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SqlDataReader rdr = SqlHelper.ExecuteReader(SqlHelper.ConnectionStringLocalTransaction, CommandType.Text,SQL_SELECT_CATEGORIES, null) ;
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while (rdr.Read())
4![](/Images/OutliningIndicators/ExpandedSubBlockStart.gif)
{
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CategoryInfo cat = new CategoryInfo(rdr.GetString(0), rdr.GetString(1), rdr.GetString(2));
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categories.Add(cat);
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}
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return categories;
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}
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finally
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{rdr .Dispose()}
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这种用法的要求是在using()括号里面的类要实现IDisposable接口,否则的话变异的时候会出错!
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![](/Images/OutliningIndicators/ExpandedBlockEnd.gif)
在第6行处用到了using,这里我想提醒自己的是,这是using的一种用法之一。
using共有三种用法:
1.引用命名空间,减少冗余代码。
Using System.Web.UI.WebControls;
2.创建命名空间的别名(using 别名)。
using MyAlias = MyCompany.Proj.Nested;
3.即时释放资源。
Using (TestObject a = new TestObject())
{
// 使用对象
}
//对象资源被释放
上面代码其实等同于:
![](/Images/OutliningIndicators/ContractedBlock.gif)
![](/Images/OutliningIndicators/ExpandedBlockStart.gif)
1
![](/Images/OutliningIndicators/ExpandedBlockStart.gif)
![](/Images/OutliningIndicators/ContractedBlock.gif)
![](/Images/dot.gif)
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![](/Images/OutliningIndicators/InBlock.gif)
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![](/Images/OutliningIndicators/InBlock.gif)
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![](/Images/OutliningIndicators/ExpandedSubBlockStart.gif)
![](/Images/OutliningIndicators/ContractedSubBlock.gif)
![](/Images/dot.gif)
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![](/Images/OutliningIndicators/None.gif)
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