相信使用 C#、winforms 编写界面的朋友都遇到过在程序调用摄像头时弹出“选择摄像头源”并且摄像头展示 panel “黑屏”的情况，网上关于此类问题有相当多的提问，但回答却大多不尽人意，正好最近在写毕设时也踩到了这个坑上，研究出了一个解决办法，虽不能非常完美的解决问题，但至少能保证每次都成功启动摄像头
一、检查 .net 的版本
在网上流传的 C# 调用摄像头的案例中，大多都是使用了 avicap32.dll 与 user32.dll 等比较老的动态链接库，此类库对程序运行时的环境有要求，经测试后发现，通过这俩类库调用摄像头的代码 .net v4.0 及后的版本的环境中基本无法运行。因此，若使用了 avicap32.dll 与 user32.dll 类库调用摄像头，请确保程序运行在 .net v3.0 或更老的版本下
二、创建摄像头类 WebCamera.cs
- 系统环境：Win10 x64
- VS版本：Visual Studio 2015
- 运行环境：.net framework 3.0
using System;
using System.Runtime.InteropServices;
namespace WebcamTest
{
class WebCam
{
private const int WM_USER = 0x400;
private const int WS_CHILD = 0x40000000;
private const int WS_VISIBLE = 0x10000000;
private const int WM_CAP_START = WM_USER;
private const int WM_CAP_STOP = WM_CAP_START + 68;
private const int WM_CAP_DRIVER_CONNECT = WM_CAP_START + 10;
private const int WM_CAP_DRIVER_DISCONNECT = WM_CAP_START + 11;
private const int WM_CAP_SAVEDIB = WM_CAP_START + 25;
private const int WM_CAP_GRAB_FRAME = WM_CAP_START + 60;
private const int WM_CAP_SEQUENCE = WM_CAP_START + 62;
private const int WM_CAP_FILE_SET_CAPTURE_FILEA = WM_CAP_START + 20;
private const int WM_CAP_SEQUENCE_NOFILE = WM_CAP_START + 63;
private const int WM_CAP_SET_OVERLAY = WM_CAP_START + 51;
private const int WM_CAP_SET_PREVIEW = WM_CAP_START + 50;
private const int WM_CAP_SET_CALLBACK_VIDEOSTREAM = WM_CAP_START + 6;
private const int WM_CAP_SET_CALLBACK_ERROR = WM_CAP_START + 2;
private const int WM_CAP_SET_CALLBACK_STATUSA = WM_CAP_START + 3;
private const int WM_CAP_SET_CALLBACK_FRAME = WM_CAP_START + 5;
private const int WM_CAP_SET_SCALE = WM_CAP_START + 53;
private const int WM_CAP_SET_PREVIEWRATE = WM_CAP_START + 52;
private const int WM_CAP_EDIT_COPY = WM_USER + 30;
private IntPtr hWndC;
private bool bStat = false;
private IntPtr mControlPtr;
private int mWidth;
private int mHeight;
private int mLeft;
private int mTop;
///
/// 初始化摄像头
///
/// 控件的句柄
/// 开始显示的左边距
/// 开始显示的上边距
/// 要显示的宽度
/// 要显示的长度
public WebCam(IntPtr handle, int left, int top, int width, int height)
{
mControlPtr = handle;
mWidth = width;
mHeight = height;
mLeft = left;
mTop = top;
}
[DllImport("avicap32.dll")]
private static extern IntPtr capCreateCaptureWindowA(byte[] lpszWindowName, int dwStyle, int x, int y, int nWidth, int nHeight, IntPtr hWndParent, int nID);
[DllImport("avicap32.dll")]
private static extern int capGetVideoFormat(IntPtr hWnd, IntPtr psVideoFormat, int wSize);
[DllImport("User32.dll")]
private static extern bool SendMessage(IntPtr hWnd, int wMsg, int wParam, int lParam);
///
/// 开始显示图像
///
public void Start()
{
if (bStat)
return;
bStat = true;
byte[] lpszName = new byte[100];
hWndC = capCreateCaptureWindowA(lpszName, WS_CHILD | WS_VISIBLE, mLeft, mTop, mWidth, mHeight, mControlPtr, 0);
if (hWndC.ToInt32() != 0)
{
SendMessage(hWndC, WM_CAP_SET_CALLBACK_VIDEOSTREAM, 0, 0);
SendMessage(hWndC, WM_CAP_SET_CALLBACK_ERROR, 0, 0);
SendMessage(hWndC, WM_CAP_SET_CALLBACK_STATUSA, 0, 0);
//大力出奇迹！
while (!SendMessage(hWndC, WM_CAP_DRIVER_CONNECT, 0, 0))
{
continue;
}
SendMessage(hWndC, WM_CAP_SET_SCALE, 1, 0);
SendMessage(hWndC, WM_CAP_SET_PREVIEWRATE, 66, 0);
SendMessage(hWndC, WM_CAP_SET_OVERLAY, 1, 0);
SendMessage(hWndC, WM_CAP_SET_PREVIEW, 1, 0);
}
return;
}
///
/// 停止显示
///
public void Stop()
{
SendMessage(hWndC, WM_CAP_DRIVER_DISCONNECT, 0, 0);
bStat = false;
}
///
/// 截图并复制到粘贴板
///
public void copyToClipBoard()
{
SendMessage(hWndC, WM_CAP_EDIT_COPY, 0, 0);
}
}
}
解决办法在于：//大力出奇迹！的注释下
while (!SendMessage(hWndC, WM_CAP_DRIVER_CONNECT, 0, 0))
{
continue;
}
此处利用死循环调用 SendMessage(hWndC, WM_CAP_DRIVER_CONNECT, 0, 0) 去链接摄像头，直到返回调用成功，看似暴力的解决办法缺有效地解决了调用失败的方法。至于此方法的灵感来源，来自于反复折腾代码无果时生气地连续点击“开启摄像头”后出现的偶然成功：p
三、一个简单的调用例子 Mainform.cs
编写完摄像头类 WebCamera.cs 后，就可以新建一个窗体测试了
using System;
using System.Collections;
using System.Drawing;
using System.Drawing.Imaging;
using System.Windows.Forms;
namespace WebcamTest
{
public partial class MainForm : Form
{
WebCam webcam;
Bitmap bitmap; //存放摄像头截取图片
public MainForm()
{
InitializeComponent();
}
private void MainForm_Load(object sender, EventArgs e)
{
//程序载入时自动开启摄像头
webcam = new WebCam(panel_WebCamShower.Handle, 0, 0, panel_WebCamShower.Width, panel_WebCamShower.Height);
webcam.Start();
}
private void btn_StartCam_Click(object sender, EventArgs e)
{
//开启摄像头
webcam.Start();
}
private void btn_StopCam_Click(object sender, EventArgs e)
{
//关闭摄像头
webcam.Stop();
}
private void btn_exit_Click(object sender, EventArgs e)
{
//退出程序
Application.Exit();
}
private void btn_CopyToClipBoard_Click(object sender, EventArgs e)
{
//复制到粘贴板
webcam.copyToClipBoard();
//从粘贴板提取图片
bitmap = (Bitmap)Clipboard.GetImage();
//刷新画布
panel_ClipBoardShower.Refresh();
}
}
}
四、测试
按照上述的暴力方式改造好代码后，在测试时，选择视频源的弹框一般还会弹出一到两次，在按一到两次确定后摄像头便调用成功
发表回复