后台工作者 - 使用"sub tasks"报告进度

Question

一个带有自定义控件LabelProgressBar的WinForms应用程序，它能够显示进度和一些描述性文本和/或完成百分比。这是通过调用LabelProgressBar.statusInProgress(string message, int percentageCompletion)来完成的。

其中一个用法如下：

private void import_begin(System.Object sender, System.ComponentModel.DoWorkEventArgs args)
{
// first unpack the arguments
System.Object[] arguments = (System.Object[])args.Argument;
System.String filename = (System.String)arguments[0];
System.String why = (System.String)arguments[1];
// tasks:
// 1. read excel file and apply changes to model
// 2. gather changes and format them as XML
// 3. send request to server
// 4. commit/rollback changes
// grab the worker thread so we can report percentage progress
System.ComponentModel.BackgroundWorker worker = (System.ComponentModel.BackgroundWorker)sender;
// now do the work
#region Task1
Controller.Excel excel = new Controller.Excel(filename);
try
{
// the progress of this needs to be tracked
overall_result = excel.import_all(out modified_nodes);
}
catch (InvalidDataExcetpion invDataEx)
{
// deal with it
}
#endregion
worker.ReportProgress(25);
// complete remaining tasks...
}

工作人员报告其进度的事件处理程序如下：

private void import_progress(object sender, System.ComponentModel.ProgressChangedEventArgs e)
{
Debug.WriteLine("Import percentage completion: " + e.ProgressPercentage);
labelProgressBar1.statusInProgress("Import", e.ProgressPercentage);
}

简而言之，import_begin方法被分解为几个"任务"。这些任务被分解为"子任务"。以import_all方法为例：

public Command_Result import_all(out System.Collections.Generic.List<Model.Data_Node> nodes)
{
Command_Result overall_result = Command_Result.OK;
Command_Result this_result;
nodes = new System.Collections.Generic.List<Model.Data_Node>(excel.Workbook.Worksheets.Count);
Model.Data_Node destination;
// the intent is to report the progress of this particular subtask on the basis of how many worksheets have been processed in this for loop
foreach (OfficeOpenXml.ExcelWorksheet worksheet in excel.Workbook.Worksheets)
{
this_result = import_sheet(worksheet.Name, out destination);
nodes.Add(destination);
if (this_result > overall_result)
{
overall_result = this_result;
}
}
return overall_result;
}

目的是让这个"子任务"根据循环中处理的图纸数量来报告进度。计算百分比是一项琐碎的任务，但我不清楚如何将其报告给import_begin方法。当此"子任务"完成时，总体任务完成率(根据import_begin方法的POV(应为25%。其他任务也是如此。如何做到这一点？

Answer 1

import_begin实际上不需要获得更新，它只需要调用子任务，同时也传递BackgroundWorker，因此子任务负责直接报告其进度。如果用BackgroundWorker"污染"子任务是不可接受的，那么创建一个委托来调用BackgroundWorker，这样子任务就会调用该委托。

private void mainTask(object sender, DoWorkEventArgs e)
{
var worker = (BackgroundWorker)sender;
var report = new Action<int>(i => worker.ReportProgress(i)); //the delegate
smallTask1Clean(report); //this one pass the delegate
smallTask2(worker); //this one directly call background worker
worker.ReportProgress(100);
}
void smallTask1Clean(Action<int> a)
{
for (int i = 0; i < 20; i++)
{
Thread.Sleep(500);
a(i);
}
}
void smallTask2(BackgroundWorker w)
{
for (int i = 0; i < 5; i++)
{
Thread.Sleep(1000);
w.ReportProgress(i*80/5+20);
}
}

您还可以使子任务不必知道它们在较大任务中的作用，在这种情况下，委托应该接受两个变量，即子任务的当前内部进度和需要处理的总项目。

private void mainTask(object sender, DoWorkEventArgs e)
{
var worker = (BackgroundWorker)sender;
var preTaskProgress = 0;
var currentTaskTotalPercentage = 0;
var smarterDelegate = new Action<int, int>((current, total) =>
{
worker.ReportProgress(preTaskProgress + (current *currentTaskTotalPercentage/total));
});
currentTaskTotalPercentage = 30; //the following task will in total progressed the main task for 30%
smallTaskClean(smarterDelegate);
preTaskProgress = currentTaskTotalPercentage; //upate the main the progress before starting the next task
currentTaskTotalPercentage = 70; //the following task will in total progressed the main task for 70%
smallTaskClean(smarterDelegate);
worker.ReportProgress(100);
}
void smallTaskClean(Action<int,int> a)
{
for (int i = 0; i < 5; i++)
{
Thread.Sleep(1500);
a(i,5);
}
}