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14.2.1 要求权限
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14.2.1 要求权限
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2006-10-13 14:41:00
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<div style='float:left;width:49%'>·<a href='100165421.htm'>14.1.2 代码访问权限和权限集</a></div><div style='float:right;width:49%'>·<a href='100165422.htm'>14.1.3 策略的级别：Machine、User和Enterprise</a></div><div style='float:left;width:49%'>·<a href='100165423.htm'>14.2 对Framework中安全性的支持</a></div><div style='float:right;width:49%'>·<a href='100165425.htm'>14.2.2 请求权限</a></div><div style='float:left;width:49%'>·<a href='100165426.htm'>14.2.3 隐式的权限</a></div><div style='float:right;width:49%'>·<a href='100165427.htm'>14.2.4 拒绝权限</a></div></div>
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<div id="text"> <link href="css.css" rel="stylesheet" type="text/css" /><h3 style="MARGIN-TOP: 8.15pt; MARGIN-LEFT: 0cm; MARGIN-RIGHT: 0cm; FTEL: 8.15pt"><a ftel="_Toc507815604"><span lang="EN-US">14.2.1 </span></a><span style="FONT-FAMILY: 黑体">要求权限</span></h3>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">为了说明要求权限的工作情况，下面创建一个</span><span lang="EN-US">Windows Forms</span><span style="FONT-FAMILY: 宋体">应用程序，它包含一个按钮，当单击按钮时，应用程序就执行访问磁盘的动作。如果应用程序没有访问本地磁盘的相关权限</span><span lang="EN-US">(FileIOPermission)</span><span style="FONT-FAMILY: 宋体">，就把按钮标记为不可用</span><span lang="EN-US">(</span><span style="FONT-FAMILY: 宋体">即把按钮变为灰色</span><span lang="EN-US">)</span><span style="FONT-FAMILY: 宋体">。</span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">如果导入命名空间</span><span lang="EN-US">System.Security.Permissions</span><span style="FONT-FAMILY: 宋体">，</span> <span style="FONT-FAMILY: 宋体">就把</span><span lang="EN-US">Form1</span><span style="FONT-FAMILY: 宋体">类的构造函数改为检查权限：创建一个</span><span lang="EN-US">FileIOPermission</span><span style="FONT-FAMILY: 宋体">对象，并调用这个对象的</span><span lang="EN-US">Demand()</span><span style="FONT-FAMILY: 宋体">方法，然后对结果进行操作：</span></p>
<p class="a6" style="MARGIN-TOP: 8.15pt; MARGIN-LEFT: 21.45pt; MARGIN-RIGHT: 0cm; FTEL: 18.45pt"><span lang="EN-US"> public Form1()</span></p>
<p class="a6" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> {</span></p>
<p class="a6" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> InitializeComponent();</span></p>
<p class="a6" style="BACKGROUND: #f2f2f2; MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> try</span></p>
<p class="a6" style="BACKGROUND: #f2f2f2; MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> {</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> FileIOPermission fileioperm = new</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> FileIOPermission(FileIOPermissionAccess.AllAccess,@"c:\");</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> fileioperm.Demand();</span></p>
<p class="a6" style="BACKGROUND: #f2f2f2; MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> }</span></p>
<p class="a6" style="BACKGROUND: #f2f2f2; MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> catch</span></p>
<p class="a6" style="BACKGROUND: #f2f2f2; MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> {</span></p>
<p class="a6" style="BACKGROUND: #f2f2f2; MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> button1.Enabled = false;</span></p>
<p class="a6" style="BACKGROUND: #f2f2f2; MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> }</span></p>
<p class="a6" style="MARGIN-TOP: 0cm; MARGIN-LEFT: 21.45pt; MARGIN-RIGHT: 0cm; FTEL: 18.45pt"><span lang="EN-US"> }</span></p>
<p class="MsoNormal"><span lang="EN-US">FileIOPermission</span><span style="FONT-FAMILY: 宋体">包含在</span><span lang="EN-US">System.Security.Permissions</span><span style="FONT-FAMILY: 宋体">命名空间中。这个命名空间实际上包含了权限的全集，除此之外，它还为声明性的权限属性提供了类，为用于创建权限对象的参数提供了枚举值</span><span lang="EN-US">(</span><span style="FONT-FAMILY: 宋体">例如，在创建</span><span lang="EN-US">FileIOPermission</span><span style="FONT-FAMILY: 宋体">时，指定是需要完全访问还是只读访问</span><span lang="EN-US">)</span><span style="FONT-FAMILY: 宋体">。</span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">如果从本地磁盘中运行应用程序</span><span lang="EN-US">(</span><span style="FONT-FAMILY: 宋体">在默认状态下安全性策略允许访问本地的存储器</span><span lang="EN-US">)</span><span style="FONT-FAMILY: 宋体">，则应用程序的运行情况如图</span><span lang="EN-US">14-5</span><span style="FONT-FAMILY: 宋体">所示。</span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">但是，如果把可执行文件复制到网络的共享区域，再次运行它，则应用程序就处于</span><span lang="EN-US">LocalIntranet</span><span style="FONT-FAMILY: 宋体">权限集中，这意味着应用程序不能访问本地的存储器，按钮将变为灰色，如图</span><span lang="EN-US">14-6</span><span style="FONT-FAMILY: 宋体">所示。</span></p>
<p align="center"><span lang="EN-US" style="COLOR: black"><img height="74" src="14/image005.jpg" width="192" alt="" /> <img height="73" src="14/image006.jpg" width="190" alt="" /></span></p>
<p style="FTEL: 8.15pt" align="center"><span style="COLOR: black; FONT-FAMILY: 宋体">图</span><span lang="EN-US" style="COLOR: black"> 14-5 </span><span style="COLOR: black; FONT-FAMILY: 宋体">图</span><span lang="EN-US" style="COLOR: black"> 14-6</span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">如果只是实现单击按钮时访问磁盘这一功能，则没有必要编写任何的安全代码。因为</span><span lang="EN-US">.NET Framework</span><span style="FONT-FAMILY: 宋体">中相关的类将要求文件权限，</span><span lang="EN-US">CLR</span><span style="FONT-FAMILY: 宋体">将确保堆栈中的每一个调用者在继续工作之前都能得到那些权限。如果要从内部网上运行应用程序，试图打开本地磁盘上的文件，除非安全性策略已经更改为把本地磁盘的访问权限赋予应用程序，否则将产生异常。</span><span lang="EN-US"> </span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">当代码试图违反被赋予的权限时，</span><span lang="EN-US">CLR</span><span style="FONT-FAMILY: 宋体">就会产生异常，捕获到的异常是</span><span lang="EN-US">SecurityException</span><span style="FONT-FAMILY: 宋体">类型，通过它可以访问许多有用的信息，其中包括可读的堆栈踪迹</span><span lang="EN-US">(SecurityException.StackTrace)</span><span style="FONT-FAMILY: 宋体">和对产生异常的方法的引用</span><span lang="EN-US">(SecurityException.TargetSite)</span><span style="FONT-FAMILY: 宋体">。</span><span lang="EN-US">SecurityException</span><span style="FONT-FAMILY: 宋体">甚至还能提供</span><span lang="EN-US">SecurityException.PermissionType</span><span style="FONT-FAMILY: 宋体">属性，这个属性返回导致安全异常发生的</span><span lang="EN-US">Permission</span><span style="FONT-FAMILY: 宋体">对象的类型。如果在诊断安全异常时还有问题，则问题应该发生在所调用的第一个端口。从上面的示例代码中删除</span><span lang="EN-US">try</span><span style="FONT-FAMILY: 宋体">和</span><span lang="EN-US">catch</span><span style="FONT-FAMILY: 宋体">块，就可以看到安全异常。</span></p></div>
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<h1 id="divCurrentNode2" style="color: #b83507; width: 100%; text-align: left; font-size: 12px; padding-left: 2px">当前章节:<a href='100165424.htm'><font color='red'>14.2.1 要求权限</font></a></h1>
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<div style='float:left;width:49%'>·<a href='100165421.htm'>14.1.2 代码访问权限和权限集</a></div><div style='float:right;width:49%'>·<a href='100165422.htm'>14.1.3 策略的级别：Machine、User和Enterprise</a></div><div style='float:left;width:49%'>·<a href='100165423.htm'>14.2 对Framework中安全性的支持</a></div><div style='float:right;width:49%'>·<a href='100165425.htm'>14.2.2 请求权限</a></div><div style='float:left;width:49%'>·<a href='100165426.htm'>14.2.3 隐式的权限</a></div><div style='float:right;width:49%'>·<a href='100165427.htm'>14.2.4 拒绝权限</a></div></div>
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