mixerGetLineInfo 得不到返回的结构体的字符串内容？？
想做一个XP下的音量控制方面的程序。是通过一个MFC的代码改的，但是刚到 函数mixerGetLineInfo 时就不对了...不知如何修改... 求帮助~~~
下面分别贴上 C#里面的代码 和 MFC下的代码 以及他们的执行效果图。
MFC的一段代码和效果图 如下：
要加上
#include <mmsystem.h>
#pragma comment(lib,"Winmm.lib")
C# 的一段代码和效果图 如下：
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Runtime.InteropServices;
namespace _cs_test
{
public partial class Form1 : Form
{
public const uint MAXPNAMELEN = 32;
public const uint CALLBACK_WINDOW = 0x00010000;
public const uint MIXER_OBJECTF_MIXER = 0x00000000;
public const uint MMSYSERR_NOERROR = 0;
public const uint MIXERLINE_COMPONENTTYPE_DST_SPEAKERS = 4;
public const uint MIXER_OBJECTF_HANDLE = 0x80000000;
public const uint MIXER_OBJECTF_HMIXER = (MIXER_OBJECTF_HANDLE | MIXER_OBJECTF_MIXER);
public const uint MIXER_GETLINEINFOF_COMPONENTTYPE = 0x00000003;
public const uint MIXER_SHORT_NAME_CHARS = 16;
public const uint MIXER_LONG_NAME_CHARS = 64;
// *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** ***
[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)]
public struct MIXERCAPSW
{
ushort wMid; /* manufacturer id */
ushort wPid; /* product id */
uint vDriverVersion; /* version of the driver */
[MarshalAs(UnmanagedType.ByValTStr, SizeConst = (int)MAXPNAMELEN)]
String szPname; /* product name */
uint fdwSupport; /* misc. support bits */
uint cDestinations; /* count of destinations */
}
[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)]
public struct MIXERLINEW
{
public uint cbStruct; /* size of MIXERLINE structure */
public uint dwDestination; /* zero based destination index */
public uint dwSource; /* zero based source index (if source) */
public uint dwLineID; /* unique line id for mixer device */
public uint fdwLine; /* state/information about line */
public uint dwUser; /* driver specific information */
public uint dwComponentType; /* component type line connects to */
public uint cChannels; /* number of channels line supports */
public uint cConnections; /* number of connections [possible] */
public uint cControls; /* number of controls at this line */
[MarshalAs(UnmanagedType.ByValTStr, SizeConst = (int)MIXER_SHORT_NAME_CHARS)] // 16
public String szShortName;
[MarshalAs(UnmanagedType.ByValTStr, SizeConst = (int)MIXER_LONG_NAME_CHARS)] // 64
public String szName;
//public struct Target
//{
public uint dwType; /* MIXERLINE_TARGETTYPE_xxxx */
public uint dwDeviceID; /* target device ID of device type */
public ushort wMid; /* of target device */
public ushort wPid; /* " */
public uint vDriverVersion; /* " */
[MarshalAs(UnmanagedType.ByValTStr, SizeConst = (int)MAXPNAMELEN)] // 32
public String szPname; /* " */
//}
}
// *** ***
[DllImport("Winmm.dll", SetLastError = true, EntryPoint = "mixerGetNumDevs")]
public static extern uint mixerGetNumDevs();
[DllImport("Winmm.dll", SetLastError = true, EntryPoint = "mixerOpen")]
public static extern uint mixerOpen(
ref IntPtr phmx,
uint uMxId,
IntPtr dwCallback,
IntPtr dwInstance,
uint fdwOpen);
[DllImport("Winmm.dll", SetLastError = true, EntryPoint = "mixerGetDevCaps")]
public static extern uint mixerGetDevCaps(
IntPtr uMxId,
ref MIXERCAPSW pmxcaps,
uint cbmxcaps);
[DllImport("Winmm.dll", SetLastError = true, EntryPoint = "mixerGetLineInfo")]
public static extern uint mixerGetLineInfo(
IntPtr hmxobj,
ref MIXERLINEW pmxl,
uint fdwInfo);
// *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** ***
public Form1()
{
InitializeComponent();
}
uint m_nNumMixers = 0;
IntPtr m_hMixer = IntPtr.Zero;
MIXERCAPSW m_mxcaps = new MIXERCAPSW();
private void button1_Click(object sender, EventArgs e)
{
m_nNumMixers = mixerGetNumDevs();
//MessageBox.Show("m_nNumMixers : " + m_nNumMixers.ToString());
if (m_nNumMixers != 0)
{
uint uiRtn = mixerOpen(
ref m_hMixer,
0,
this.Handle,
IntPtr.Zero,
MIXER_OBJECTF_MIXER | CALLBACK_WINDOW);
if (uiRtn != MMSYSERR_NOERROR)
{
MessageBox.Show("mixerOpen failed");
return;
}
uiRtn = mixerGetDevCaps(m_hMixer, ref m_mxcaps, (uint)Marshal.SizeOf(m_mxcaps));
if (uiRtn != MMSYSERR_NOERROR)
{
MessageBox.Show("mixerGetDevCaps failed");
return;
}
}
if (m_hMixer == IntPtr.Zero)
{
MessageBox.Show("m_hMixer == IntPtr.Zero");
return;
}
// get dwLineID
MIXERLINEW mxl = new MIXERLINEW();
mxl.cbStruct = (uint)Marshal.SizeOf(mxl);
mxl.dwComponentType = MIXERLINE_COMPONENTTYPE_DST_SPEAKERS;
uint uiRst = mixerGetLineInfo(
m_hMixer,
ref mxl,
MIXER_OBJECTF_HMIXER | MIXER_GETLINEINFOF_COMPONENTTYPE);
if (uiRst != MMSYSERR_NOERROR)
{
MessageBox.Show("mixerGetLineInfo return : " + Convert.ToString(uiRst, 16));
return;
}
MessageBox.Show(" mxl.dwLineID : " + ((int)mxl.dwLineID).ToString() + " , " + Convert.ToString(mxl.dwLineID, 16) + "\r\n mxl.szName : " + mxl.szName);
// 本来是想将 mxl.szName 的内容显示在界面上，但是这里居然是空的...MFC里面是有值的啊，在C#里面该怎么弄啊？？
// 要怎么样改才能像MFC显示的效果那样显示“音量控制”啊？
}
}
}
C#里面的效果如上图，mxl.szName 里面是空的，但是 上面的MFC的效果是有值“音量控制”的啊，该要怎么改啊？？
求指点啊~~~
[解决办法]
http://www.cnblogs.com/zll922/archive/2009/07/10/1520576.html
[解决办法]
你定义了Unicode的MIXERLINEW结构，却可能使用了Ansi版的函数入口。
试试把入口也定为Unicode版本：
[DllImport("Winmm.dll", SetLastError = true, EntryPoint = "mixerGetDevCapsW")]
...
[DllImport("Winmm.dll", SetLastError = true, EntryPoint = "mixerGetLineInfoW")]
...