【问题】
C#中，调试一个BackgroundWorker，发现一个问题：
DoWork在第一次执行完毕后，接下来，又进入了DoWork，
即DoWork被调用了多次。
【解决过程】
1.后来参考：
DoWork of BackgroundWorker is called twice when RunWorkerAsync is called once?
所以去看了看自己的代码，也是+=：
private void getUrlRespStreamBytes_bw(ref Byte[] respBytesBuf,
string url,
Dictionary<string, string> headerDict,
Dictionary<string, string> postDict,
int timeout,
Action<int> funcUpdateProgress)
{
// Create a background thread
gBgwDownload.DoWork += new DoWorkEventHandler(bgwDownload_DoWork);
gBgwDownload.RunWorkerCompleted += new RunWorkerCompletedEventHandler(bgwDownload_RunWorkerCompleted);
gBgwDownload.WorkerReportsProgress = true;
gBgwDownload.ProgressChanged += new ProgressChangedEventHandler(bgwDownload_ProgressChanged);
//init
bNotCompleted_download = true;
gFuncUpdateProgress = funcUpdateProgress;
// run in another thread
object paraObj = new object[] {respBytesBuf, url, headerDict, postDict, timeout};
gBgwDownload.RunWorkerAsync(paraObj);
}所以就去把加号去掉：
private void getUrlRespStreamBytes_bw(ref Byte[] respBytesBuf,
string url,
Dictionary<string, string> headerDict,
Dictionary<string, string> postDict,
int timeout,
Action<int> funcUpdateProgress)
{
// Create a background thread
gBgwDownload.DoWork = new DoWorkEventHandler(bgwDownload_DoWork);
gBgwDownload.RunWorkerCompleted = new RunWorkerCompletedEventHandler(bgwDownload_RunWorkerCompleted);
gBgwDownload.WorkerReportsProgress = true;
gBgwDownload.ProgressChanged = new ProgressChangedEventHandler(bgwDownload_ProgressChanged);
//init
bNotCompleted_download = true;
gFuncUpdateProgress = funcUpdateProgress;
// run in another thread
object paraObj = new object[] {respBytesBuf, url, headerDict, postDict, timeout};
gBgwDownload.RunWorkerAsync(paraObj);
}试试结果。
结果却是，直接语法错误，都无法运行。
2.同样参考上贴，去改为，去掉new handler的形式：
private void getUrlRespStreamBytes_bw(ref Byte[] respBytesBuf,
string url,
Dictionary<string, string> headerDict,
Dictionary<string, string> postDict,
int timeout,
Action<int> funcUpdateProgress)
{
// Create a background thread
gBgwDownload.DoWork += bgwDownload_DoWork;
gBgwDownload.RunWorkerCompleted += bgwDownload_RunWorkerCompleted;
gBgwDownload.WorkerReportsProgress = true;
gBgwDownload.ProgressChanged += bgwDownload_ProgressChanged;
//init
bNotCompleted_download = true;
gFuncUpdateProgress = funcUpdateProgress;
// run in another thread
object paraObj = new object[] {respBytesBuf, url, headerDict, postDict, timeout};
gBgwDownload.RunWorkerAsync(paraObj);
}试试结果，结果问题依旧。
第二次调用DoWork后，紧接着，还是直接进入DoWork，而不是重新执行别的函数。
3.再去自己改为新建一个变量，而不是始终使用那个全局变量：
private void getUrlRespStreamBytes_bw(ref Byte[] respBytesBuf,
string url,
Dictionary<string, string> headerDict,
Dictionary<string, string> postDict,
int timeout,
Action<int> funcUpdateProgress)
{
// Create a background thread
gBgwDownload = new BackgroundWorker();
gBgwDownload.DoWork += bgwDownload_DoWork;
gBgwDownload.RunWorkerCompleted += bgwDownload_RunWorkerCompleted;
gBgwDownload.WorkerReportsProgress = true;
gBgwDownload.ProgressChanged += bgwDownload_ProgressChanged;
//init
bNotCompleted_download = true;
gFuncUpdateProgress = funcUpdateProgress;
// run in another thread
object paraObj = new object[] {respBytesBuf, url, headerDict, postDict, timeout};
gBgwDownload.RunWorkerAsync(paraObj);
}试试，结果就可以了。
【总结】
BackgroundWorker的DoWork被执行多次，原因是
之前BackgroundWorker初始化的时候，DoWork赋值时，都是
new DoWorkEventHandler
的形式，所以每次都新加了个DoWork动作，所以会导致后续多次调用时，被执行多次。
另外，不能每次都
gBgwValue += xx_doWork;
否则，也还是会多把后续的多次的DoWork都加到同一个全局变量gBgwValue上，导致后续DoWork被多次调用执行；
最终，改为，不带new DoWorkEventHandler的，每次是新建一个BackgroundWorker的变量，就可以了：
private BackgroundWorker gBgwDownload;
private void yourFunction_bw(xxx)
{
// Create a background thread
gBgwDownload = new BackgroundWorker(); /* added this line will fix problem */
gBgwDownload.DoWork += bgwDownload_DoWork;
gBgwDownload.RunWorkerCompleted += bgwDownload_RunWorkerCompleted;
//omited some code
gBgwDownload.RunWorkerAsync(paraObj);
}