private static extern bool EnumPrinters([MarshalAs(UnmanagedType.U4)] PRINTER_ENUM flags,
[MarshalAs(UnmanagedType.LPStr)] string sName,
uint iLevel,
IntPtr pPrinterDesc,
uint iSize,
[MarshalAs(UnmanagedType.U4)] ref uint iNeeded,
[MarshalAs(UnmanagedType.U4)] ref uint iReturned
);
private static extern bool EnumPrinters(PRINTER_ENUM Flags, string Name, int Level, IntPtr pPrinterEnum, int cbBuf, out int pcbNeeded, out int pcReturned);
public PrinterInfo[] Search(PRINTER_ENUM printerKind)
{
PrinterInfo[] pInfo = new PrinterInfo[0];
uint iNeeded = 0, iReturned = 0, iSize = 0;
IntPtr printers = IntPtr.Zero;
if (!EnumPrinters(printerKind, String.Empty, 1, printers, 0, ref iNeeded, ref iReturned))
{
//返回由上一个非托管函数返回的错误代码，该函数是使用设置了 -
//DllImport属性中SetLastError=true 标志的平台调用来调用的
int err = Marshal.GetLastWin32Error();
if (err != Win32Error.ERROR_INSUFFICIENT_BUFFER)
{
ThrowEnumPrinterException();
}
}
iSize = iNeeded;
if (iNeeded != 0)
{
try
{
//使用AllocHGlobal分配非托管内块
printers = Marshal.AllocHGlobal(new IntPtr(iSize));
//如果调用不成功抛出异常
if (!EnumPrinters(printerKind, String.Empty, 1, printers, iSize, ref iNeeded, ref iReturned))
{
ThrowEnumPrinterException();
}
else
{
pInfo = GetPrinterInfoFromMemory(printers, iReturned);
}
}
finally
{
//释放分配的内存块
if (printers != IntPtr.Zero)
{
Marshal.FreeHGlobal(printers);
}
}
}
return(pInfo);
}
private static extern bool EnumPrinters(PRINTER_ENUM Flags, string Name, int Level, IntPtr pPrinterEnum, int cbBuf, out int pcbNeeded, out int pcReturned);
