微软.net精简框架常见问题及回答(中文版)(28)
'VB
Shared Sub Main(ByVal args() As String)
'Do your thing here
End Sub
在Visual Studio 2003中测试的时候，可以通过继承开发环境设置命令行的参数。主菜单，选择 Project->Project Name Properties. 在Property Pages对话框中，选择 Configuration Properties->Debugging。在 Command Line Arguments 中输入字符串：text box.
7.26. 当使用已经释放的对象的方法或属性的时候，为什么得到一个异常？
完整的.net框架不保证，在访问一个已经释放的对象的属性或方法时能成功。在完整的.net框架下，虽然访问某些属性(像Text)，经常能成功。根据.net框架和.net精简框架执行上的区别，在.net精简框架上访问已经释放了的对象的方法或属性会经常失败。
7.27. 如何获得"Enter", "TAB", 和 "Arrow"按键的事件？
使用KeyDown和KeyUp事件，可以获得无字符的键(像tab)。
现在，只有一些特定的控件支持key的事件(如，form, panel, textbox 和自定义控件)。在.net精简框架SP2版本中，所有控件都将支持key事件。
已经知道的问题，在使用模拟器时，从键盘按下tab键将不被支持，但从软键盘(SIP)上按下tab时，会有效果。
这是VS带的模拟器的原因造成，而不是.net精简框架的问题。.net精简框架触发Key事件当它收到系统传来的WM_KEY*消息。当您在模拟器中运行本地代码程序时，从键盘按下tab键并不会让系统触发WM_KEYDOWN事件。若是通过模拟器的软键盘(SIP)，或真正的设备，则不会有这个问题。
7.28. 如何删除一个只读文件？
使用System.IO.FileInfo类访问文件的属性。 //C#
System.IO.FileInfo fi = new System.IO.FileInfo("filename");
// remove readonly attribute
fi.Attributes -= System.IO.FileAttributes.ReadOnly;
System.IO.File.Delete("filename");
'VB
Dim fi As New System.IO.FileInfo("filename")
'remove readonly attribute
fi.Attributes -= IO.FileAttributes.ReadOnly
System.IO.File.Delete("filename")
7.29. How do I determine if a member exists at runtime?
The existence of a member can be determined at runtime using Reflection. The code below demonstrates how to use Reflection to access the "Width" property and the "GetPixel" method of a Bitmap object. In the case of the "Width" property, the code enumerates all "public" properties with a "get" component and then searches for one named "Width". The "GetPixel" sample demonstrates how one might use Reflection to call a known function where the parameter order is unknown. This sample is set up as if the author knows there is a method named "GetPixel" which takes a pixel location of x,y but does not know the order in which they appear in the parameter list. The sample enumerates the methods and searches for one named "GetPixel" and then enumerates the parameter list to determine whether the first or second parameter is named "X". Keep in mind that, due to the differences in hardware pixel formats, the value returned by GetPixel may be different from that set by SetPixel in this sample.
Reflection provides many powerful tools for determing functionality at runtime so for information, refer to the documentation regarding System.Type and the namespace System.Reflection.
//C#
using System.Reflection;
using System.Drawing;
Bitmap bm = new Bitmap(200, 100);
int width = 0;
// Explicitly set one pixel for testing
int x = 199;
int y = 20;
Color pixColor = Color.Black;
bm.SetPixel(x,y,Color.Magenta);
// Get the "Width" property
PropertyInfo[] propInfo =
bm.GetType().GetProperties(BindingFlags.GetProperty |
BindingFlags.Public | BindingFlags.Instance);
for (int i = 0; i < propInfo.Length; i++)
{
if (propInfo[i].Name == "Width")
{
width = (int)propInfo[i].GetValue(bm, null);
break;
}
}
// Call the GetPixel method
MethodInfo[] methInfo = bm.GetType().GetMethods(BindingFlags.Public | BindingFlags.Instance);
for (int i = 0; i < methInfo.Length; i++)
{
if (methInfo[i].Name == "GetPixel")
{
ParameterInfo[] paramInfo = methInfo[i].GetParameters();
if (paramInfo.Length == 2)
{
object[] xy = new object[2];
if (paramInfo[0].Name == "x")
{
xy[0] = x;
xy[1] = y;
}
else
{
xy[1] = x;
xy[0] = y;
}
pixColor = (Color)methInfo[i].Invoke(bm, xy);
break;
}
