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我有一个主要遵循MVVM模式编写的小型WPF应用程序。程序的要点是读取文本文件的行，解析数据，将数据写入对象列表，然后将这些对象中的数据写入特定格式的.CSV文件。如何使用MVVM/ICommand模式在WPF中正确实现BackgroundWorker
尽管我已经使用与其他应用程序一样的方式实现BackgroundWorker类，但是这次我从我的ICommand的Execute（）方法中调用RunWorkAsync（）方法。虽然最终输出是正确的，并且应用程序实际上提供了期望的结果，但在BackgroundWorker运行时，UI STILL锁定。
我用一个构造函数将我的BackgroundWorker成员和一个名为“ReaderWriter”的类中的所有逻辑都包含在我的ViewModel中作为参数。
通过调用我的ReaderWriter实例的“StartProcess”方法，BackgroundWorker的RunWorkerAsync（）被调用 - 这是我希望它会接管另一个线程并执行长时间运行的读取源文件的过程，解析数据并写入新文件;同时定期执行ReportProgress（）来更新ProgressBar。
这里是我的读写器类的代码：
class ReaderWriter
{
private LogDataViewModel vm { get; set; }
private BackgroundWorker bw { get; set; }
public ReaderWriter(LogDataViewModel viewModel)
{
vm = viewModel;
}
public void StartProcess()
{
bw = new BackgroundWorker();
bw.WorkerReportsProgress = true;
bw.WorkerSupportsCancellation = true;
bw.DoWork += new DoWorkEventHandler(ReadFromSource);
bw.ProgressChanged += new ProgressChangedEventHandler(UpdateProgress_Read);
bw.RunWorkerCompleted += new RunWorkerCompletedEventHandler(Completed_Read);
bw.RunWorkerAsync();
}
private void ReadFromSource(object sender, DoWorkEventArgs e)
{
double records = 0;
string[] lines = File.ReadAllLines(vm.SourcePath);
int lineCount = lines.Length;
double currentLine = 0;
bw.ReportProgress(0, lineCount);
foreach (var line in lines)
{
if (line.Length > 0)
{
string syntax = line.Substring(17, 6);
switch (syntax)
{
case "$WIMDA":
string[] segments = line.Replace(": <- ", ",").Split(',');
vm.LineItems.Add(new LineItem()
{
Time = segments[0],
HgPressure = segments[2],
BarPressure = segments[4],
AirTemp = segments[6],
RelHumidity = segments[10],
TrueWindDir = segments[14],
KnotsWindSpeed = segments[18],
MpsWindSpeed = segments[20]
});
break;
case "$GPGGA":
break;
default:
break;
}
}
currentLine++;
bw.ReportProgress(1, currentLine);
}
using (StreamWriter writer = new StreamWriter(vm.OutputPath))
{
writer.WriteLine($"Time,Pressure(Bar),Pressure(Hg),AirTemp({((vm.ConvertTempSetting) ? "F" : "C")}),RelativeHumidity,TrueWindDirection,WindSpeed(Knots),WindSpeed(M/s)");
foreach (var lineItem in vm.LineItems)
{
writer.WriteLine($"{lineItem.Time},{lineItem.BarPressure},{lineItem.HgPressure},{((vm.ConvertTempSetting) ? Converters.ConvertFromCelcius(Convert.ToDouble(lineItem.AirTemp)).ToString() : lineItem.AirTemp)},{lineItem.RelHumidity},{lineItem.TrueWindDir},{lineItem.KnotsWindSpeed},{lineItem.MpsWindSpeed}");
records++;
}
}
e.Result = records;
}
private void UpdateProgress_Read(object sender, ProgressChangedEventArgs e)
{
vm.IncrementProgress();
switch (Type.GetTypeCode(e.UserState.GetType()))
{
case TypeCode.Double:
vm.IncrementProgress();
break;
case TypeCode.String:
break;
case TypeCode.Int32:
vm.AppendStatus(DateTime.Now, $"{(int)e.UserState} lines parsed from log file");
break;
default:
break;
}
if (vm.IsFirst)
{
vm.ProgressIsVisible = true;
vm.IncrementProgress();
vm.SetMaximum((int)e.UserState);
vm.IsFirst = false;
}
}
private void Completed_Read(object sender, RunWorkerCompletedEventArgs e)
{
if (e.Cancelled)
{
vm.AppendStatus(DateTime.Now, $"Conversion was cancelled by user");
}
else
{
vm.AppendStatus(DateTime.Now, $"{(double)e.Result} records written to {vm.OutputPath}");
}
vm.LineItems.Clear();
}
}
而对于我的ViewModel：
public class LogDataViewModel : LogDataModel
{
#region Commands
public BeginProcessCommand BeginCommand { get; set; }
public SelectOutputPathCommand OutputCommand { get; set; }
public SelectSourceCommand SourceCommand { get; set; }
public ResetCommand ResetCommand { get; set; }
#endregion
public bool IsFirst { get; set; }
public LogDataViewModel()
{
BeginCommand = new BeginProcessCommand(this);
OutputCommand = new SelectOutputPathCommand(this);
SourceCommand = new SelectSourceCommand(this);
ResetCommand = new ResetCommand(this);
PrepareViewModel();
}
private void PrepareViewModel()
{
ProgressValue = 0;
ProgressMaximum = 0;
ProgressIsVisible = false;
IsFirst = true;
OutputPath = Properties.Settings.Default.RememberedSavePath;
if (LineItems == null) LineItems = new List<LineItem>();
if (StatusActions == null) StatusActions = new ObservableCollection<StatusAction>();
AppendStatus(DateTime.Now, "Initialized Program");
}
}
最后，这里是命令：
public class BeginProcessCommand : ICommand
{
LogDataViewModel vm;
public BeginProcessCommand(LogDataViewModel viewModel)
{
vm = viewModel;
}
public event EventHandler CanExecuteChanged
{
add { CommandManager.RequerySuggested += value; }
remove { CommandManager.RequerySuggested -= value; }
}
public bool CanExecute(object parameter)
{
bool result = true;
if (!File.Exists(vm.SourcePath))
result = false;
try
{
if (!Directory.Exists(Path.GetDirectoryName(vm.SourcePath)))
result = false;
}
catch
{
result = false;
}
return result;
}
public void Execute(object parameter)
{
ReaderWriter rw = new ReaderWriter(vm);
rw.StartProcess();
}
}
任何帮助的这一点非常感谢，因为我现在一直在努力研究这个问题，并试图研究解决方案对我的特殊情况没有帮助。这似乎是一个相当独特的场景，但我希望我们可以使它工作。
谢谢！
这是因为你用更新来暴露用户界面。每100行只尝试报告进度。如果你有很多线条，并且循环快速旋转，那么就是这个数字。 – Will
谢谢，威尔。我做了你的建议，它像一个魅力工作！ –