Question

以下是I类工作的缩减版本（WinForms项目的一部分）：

class ReportBuilder {
    private List<Project> projects;
    private List<Invoice> invoices;
    private MyAPI apiObject;

    public ReportBuilder(MyAPI apiAccess, List<Project> selectedProjects){
        this.apiObject = apiAccess;
        this.projects = selectedProjects;
    }

    public void DownloadData(){
        BackgroundWorker workerThread = new BackgroundWorker();
        workerThread.DoWork += (sender, e) => this.retrieveInvoices(this.projects); // yes, the parameter is unnecessary in this case, since the variable is in scope for the method anyway, but I'm doing it for illustrative purposes
        workerThread.RunWorkerCompleted += receiveData;
        workerThread.RunWorkerAsync();
    }

    private void retrieveInvoices(List<Project> filterProjects){
        Notification status;
        if (filterProjects == null){this.invoices = this.apiObject.GetInvoices(out status);}
        else {this.invoices = this.apiObject.GetInvoices(filterProjects, out status);}
    }

    private void receiveData(Object sender, RunWorkerCompletedEventArgs e){
        // display a save file dialog to the user
        // call a method in another class to create a report in csv format
        // save that csv to file

        // ... ideally, this method would to have access to the 'status' Notification object from retrieveInvoices, but it doesn't (unless I make that an instance variable)
    }
}

现在，通常DoWork事件处理程序的方法签名是这样的：

private void retrieveInvoices(object sender, DoWorkEventArgs e)

但是，正如您在上面所看到的，我的retrieveInvoices方法的签名并不匹配。因此我预计它会失败（要么不编译，要么只在UI线程上运行retrieveInvoices，阻止它，而不是在后台工作程序中）。令我惊讶的是，它似乎正在起作用，但由于我见过的所有BackgroundWorker示例都没有这样做，我仍然认为我必须做错事。但是我，为什么？

Answer 1

该行：

worker.DoWork += (sender, e) => this.retrieveInvoices(this.projects);

引入一个参数(object sender, DoWorkEventArgs e)的委托，该参数使用参数retrieveInvoices调用方法projects。没有语法不匹配。

这相当于：

worker.DoWork += (sender, e) => { this.retrieveInvoices(this.projects); }

或

void doSomething(object sender, System.ComponentModel.DoWorkEventArgs e)
{
    this.retrieveInvoices(this.projects);
}

worker.DoWork += doSomething;

要使用retrieveInvoices作为实际的事件处理程序，您必须写：

worker.DoWork += retrieveInvoices;

会导致不匹配。

BTW BackgroundWorker已经过时了。使用Task.Run，async / await和IProgress可以完成它所做的任何事情。例如，BGW不能用于组合多个异步操作。 `async / await同样容易，例如：

async Task<Report> RunReport(Project[] projects, IProgress<string> progress)
{
    var data= await retrieveInvoices(projects);
    progress.Report("Invoices retrieved");
    var report=await render(data);
    progress.Report("Report rendered");
    await SaveReport(report);
    progress.Report("Report saved");
    return report;
}

//...
Progress<string> progress=new Progress<string>(msg=>statusBar1.Text=msg);

await RunReport(projects);

为什么/如何在没有DoWorkEventArgs的情况下使用BackgroundWorker？

1 个答案: