【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+=：
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 | 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：
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 | 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：
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 | 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：
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 | 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：
1 2 3 4 5 6 7 8 9 10 11 | 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);} |