C# [Out] [MarshalAs(..)转到VB.NET
C# [Out] [MarshalAs(..)转到VB.NET
提问于 2018-09-19 06:10:50
我正在将C#代码转换为VB.NET，下面这行代码让我头疼：
int GetChannelCount(
[Out] [MarshalAs(UnmanagedType.U4)] out UInt32 channelCount);在线转换器不知道如何处理
[Out]我理解"out“(应该是"ByRef")，但我不知道"Out”是做什么的，也不知道如何将它转换为VB.NET。
谢谢。
ps:这是完整的代码，如果重要的话：
[Guid("5CDF2C82-841E-4546-9722-0CF74078229A"),InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
public interface IAudioEndpointVolume
{
[PreserveSig]
int NotImpl1();
[PreserveSig]
int NotImpl2();
/// <summary>
/// Gets a count of the channels in the audio stream.
/// </summary>
/// <param name="channelCount">The number of channels.</param>
/// <returns>An HRESULT code indicating whether the operation passed of failed.</returns>
[PreserveSig]
int GetChannelCount(
[Out] [MarshalAs(UnmanagedType.U4)] out UInt32 channelCount);
/// <summary>
/// Sets the master volume level of the audio stream, in decibels.
/// </summary>
/// <param name="level">The new master volume level in decibels.</param>
/// <param name="eventContext">A user context value that is passed to the notification callback.</param>
/// <returns>An HRESULT code indicating whether the operation passed of failed.</returns>
[PreserveSig]
int SetMasterVolumeLevel(
[In] [MarshalAs(UnmanagedType.R4)] float level,
[In] [MarshalAs(UnmanagedType.LPStruct)] Guid eventContext);
/// <summary>
/// Sets the master volume level, expressed as a normalized, audio-tapered value.
/// </summary>
/// <param name="level">The new master volume level expressed as a normalized value between 0.0 and 1.0.</param>
/// <param name="eventContext">A user context value that is passed to the notification callback.</param>
/// <returns>An HRESULT code indicating whether the operation passed of failed.</returns>
[PreserveSig]
int SetMasterVolumeLevelScalar(
[In] [MarshalAs(UnmanagedType.R4)] float level,
[In] [MarshalAs(UnmanagedType.LPStruct)] Guid eventContext);
/// <summary>
/// Gets the master volume level of the audio stream, in decibels.
/// </summary>
/// <param name="level">The volume level in decibels.</param>
/// <returns>An HRESULT code indicating whether the operation passed of failed.</returns>
[PreserveSig]
int GetMasterVolumeLevel(
[Out] [MarshalAs(UnmanagedType.R4)] out float level);
/// <summary>
/// Gets the master volume level, expressed as a normalized, audio-tapered value.
/// </summary>
/// <param name="level">The volume level expressed as a normalized value between 0.0 and 1.0.</param>
/// <returns>An HRESULT code indicating whether the operation passed of failed.</returns>
[PreserveSig]
int GetMasterVolumeLevelScalar(
[Out] [MarshalAs(UnmanagedType.R4)] out float level);
/// <summary>
/// Sets the volume level, in decibels, of the specified channel of the audio stream.
/// </summary>
/// <param name="channelNumber">The channel number.</param>
/// <param name="level">The new volume level in decibels.</param>
/// <param name="eventContext">A user context value that is passed to the notification callback.</param>
/// <returns>An HRESULT code indicating whether the operation passed of failed.</returns>
[PreserveSig]
int SetChannelVolumeLevel(
[In] [MarshalAs(UnmanagedType.U4)] UInt32 channelNumber,
[In] [MarshalAs(UnmanagedType.R4)] float level,
[In] [MarshalAs(UnmanagedType.LPStruct)] Guid eventContext);
/// <summary>
/// Sets the normalized, audio-tapered volume level of the specified channel in the audio stream.
/// </summary>
/// <param name="channelNumber">The channel number.</param>
/// <param name="level">The new master volume level expressed as a normalized value between 0.0 and 1.0.</param>
/// <param name="eventContext">A user context value that is passed to the notification callback.</param>
/// <returns>An HRESULT code indicating whether the operation passed of failed.</returns>
[PreserveSig]
int SetChannelVolumeLevelScalar(
[In] [MarshalAs(UnmanagedType.U4)] UInt32 channelNumber,
[In] [MarshalAs(UnmanagedType.R4)] float level,
[In] [MarshalAs(UnmanagedType.LPStruct)] Guid eventContext);
/// <summary>
/// Gets the volume level, in decibels, of the specified channel in the audio stream.
/// </summary>
/// <param name="channelNumber">The zero-based channel number.</param>
/// <param name="level">The volume level in decibels.</param>
/// <returns>An HRESULT code indicating whether the operation passed of failed.</returns>
[PreserveSig]
int GetChannelVolumeLevel(
[In] [MarshalAs(UnmanagedType.U4)] UInt32 channelNumber,
[Out] [MarshalAs(UnmanagedType.R4)] out float level);
/// <summary>
/// Gets the normalized, audio-tapered volume level of the specified channel of the audio stream.
/// </summary>
/// <param name="channelNumber">The zero-based channel number.</param>
/// <param name="level">The volume level expressed as a normalized value between 0.0 and 1.0.</param>
/// <returns>An HRESULT code indicating whether the operation passed of failed.</returns>
[PreserveSig]
int GetChannelVolumeLevelScalar(
[In] [MarshalAs(UnmanagedType.U4)] UInt32 channelNumber,
[Out] [MarshalAs(UnmanagedType.R4)] out float level);
/// <summary>
/// Sets the muting state of the audio stream.
/// </summary>
/// <param name="isMuted">True to mute the stream, or false to unmute the stream.</param>
/// <param name="eventContext">A user context value that is passed to the notification callback.</param>
/// <returns>An HRESULT code indicating whether the operation passed of failed.</returns>
[PreserveSig]
int SetMute(
[In] [MarshalAs(UnmanagedType.Bool)] Boolean isMuted,
[In] [MarshalAs(UnmanagedType.LPStruct)] Guid eventContext);
/// <summary>
/// Gets the muting state of the audio stream.
/// </summary>
/// <param name="isMuted">The muting state. True if the stream is muted, false otherwise.</param>
/// <returns>An HRESULT code indicating whether the operation passed of failed.</returns>
[PreserveSig]
int GetMute(
[Out] [MarshalAs(UnmanagedType.Bool)] out Boolean isMuted);
/// <summary>
/// Gets information about the current step in the volume range.
/// </summary>
/// <param name="step">The current zero-based step index.</param>
/// <param name="stepCount">The total number of steps in the volume range.</param>
/// <returns>An HRESULT code indicating whether the operation passed of failed.</returns>
[PreserveSig]
int GetVolumeStepInfo(
[Out] [MarshalAs(UnmanagedType.U4)] out UInt32 step,
[Out] [MarshalAs(UnmanagedType.U4)] out UInt32 stepCount);
/// <summary>
/// Increases the volume level by one step.
/// </summary>
/// <param name="eventContext">A user context value that is passed to the notification callback.</param>
/// <returns>An HRESULT code indicating whether the operation passed of failed.</returns>
[PreserveSig]
int VolumeStepUp(
[In] [MarshalAs(UnmanagedType.LPStruct)] Guid eventContext);
/// <summary>
/// Decreases the volume level by one step.
/// </summary>
/// <param name="eventContext">A user context value that is passed to the notification callback.</param>
/// <returns>An HRESULT code indicating whether the operation passed of failed.</returns>
[PreserveSig]
int VolumeStepDown(
[In] [MarshalAs(UnmanagedType.LPStruct)] Guid eventContext);
/// <summary>
/// Queries the audio endpoint device for its hardware-supported functions.
/// </summary>
/// <param name="hardwareSupportMask">A hardware support mask that indicates the capabilities of the endpoint.</param>
/// <returns>An HRESULT code indicating whether the operation passed of failed.</returns>
[PreserveSig]
int QueryHardwareSupport(
[Out] [MarshalAs(UnmanagedType.U4)] out UInt32 hardwareSupportMask);
/// <summary>
/// Gets the volume range of the audio stream, in decibels.
/// </summary>
/// <param name="volumeMin">The minimum volume level in decibels.</param>
/// <param name="volumeMax">The maximum volume level in decibels.</param>
/// <param name="volumeStep">The volume increment level in decibels.</param>
/// <returns>An HRESULT code indicating whether the operation passed of failed.</returns>
[PreserveSig]
int GetVolumeRange(
[Out] [MarshalAs(UnmanagedType.R4)] out float volumeMin,
[Out] [MarshalAs(UnmanagedType.R4)] out float volumeMax,
[Out] [MarshalAs(UnmanagedType.R4)] out float volumeStep);
}回答 1
Stack Overflow用户
回答已采纳
发布于 2018-09-19 06:27:58
out是一个修饰符，它使参数由ref传递，而不需要像C#中的ref那样首先进行初始化。它意味着向传递的参数写入一个值，这样修改的方向就不在被调用的方法之外。考虑一些.NET框架类型中的TryParse()方法。
string foo = "123";
int value;
if(int.TryParse(foo, out value)) // Returns true if it can be parsed in which case, value now holds the parsed value
{
// Do something
}VB.NET对此没有等价物，因为它在默认情况下初始化变量，而您只需正常地调用它ByRef即可。在与您发布的代码一样将其与平台调用一起使用的上下文中，您只需调用Out属性，通过将数据从被调用的方法编组到调用方法，该属性对平台调用具有相同的效果。考虑以下代码：
<PreserveSig>
Function GetChannelCount(<Out, MarshalAs(UnmanagedType.U4)> ByRef channelCount As UInt32) As Integer
End Function这实际上告诉运行时，您定义的ByRef参数应该被视为out参数，可以这样说，允许被调用的方法在不需要初始化它的情况下对其进行写入。
页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/52395255
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