我收到一个错误，当我有多个异步任务时，我无法弄明白。我不能使用parallel，因为任务必须按照我排队的顺序返回。
当我第二次尝试调用PartProcessor（）时，我第二次收到错误。
processedParts = await new PartsProcessor.PartProcessor().ProcessParts(userID, elevations, true);
这有效
public async static Task<List<Bitmap>> RollUpDrawingsImageTotalsListAsync(Guid userID, IElevation[] elevations)
{
List<Bitmap> totals = new List<Bitmap>();
var processedParts = await new PartsProcessor.PartProcessor().ProcessParts(userID, elevations, false);
processedParts.Elevation = elevations[0];
totals.Add(await MaterialsList.Manager.GetMaterialListAsync(processedParts).Result.GetDrawingAsync(true));
totals.Add(await Optimization.Manager.GetOptimizedPartsAsync(processedParts).Result.GetDrawingAsync(true));
totals.Add(await CutSheet.Manager.GetCutSheet(processedParts).GetDrawingAsync(true));
return totals;
}
但是当我的方法体看起来如此时，我得到了这个错误：“注意我是如何在totals.Add（等待CutSheet ......”之后添加PartProcessor的。“
public async static Task<List<Bitmap>> RollUpDrawingsImageTotalsListAsync(Guid userID, IElevation[] elevations)
{
List<Bitmap> totals = new List<Bitmap>();
var processedParts = await new PartsProcessor.PartProcessor().ProcessParts(userID, elevations, false);
processedParts.Elevation = elevations[0];
totals.Add(await MaterialsList.Manager.GetMaterialListAsync(processedParts).Result.GetDrawingAsync(true));
totals.Add(await Optimization.Manager.GetOptimizedPartsAsync(processedParts).Result.GetDrawingAsync(true));
processedParts = await new PartsProcessor.PartProcessor().ProcessParts(userID, elevations, true);
totals.Add(await CutSheet.Manager.GetCutSheet(processedParts).GetDrawingAsync(true));
return totals;
}
-----------------------------------------错误----- ------------------------------
<Error>
<Message>An error has occurred.</Message>
<ExceptionMessage>
Object reference not set to an instance of an object.
</ExceptionMessage>
<ExceptionType>System.NullReferenceException</ExceptionType>
<StackTrace>
at CutSheet.CutSheet.<GetDrawingAsync>d__0.MoveNext() in c:\Users\Administrator\Documents\Visual Studio 2012\Projects\AlumCloud\CutSheet\CutSheet.cs:line 125 --- End of stack trace from previous location where exception was thrown --- at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) at System.Runtime.CompilerServices.TaskAwaiter`1.GetResult() at AlumCloudPlans.Manager.<RollUpDrawingsImageTotalsListAsync>d__33.MoveNext() in c:\Users\Administrator\Documents\Visual Studio 2012\Projects\AlumCloud\AlumCloudPlans\PlanManager.cs:line 453 --- End of stack trace from previous location where exception was thrown --- at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) at System.Runtime.CompilerServices.TaskAwaiter`1.GetResult() at AlumCloudPlans.Manager.<RollUpProjectPDFAsync>d__65.MoveNext() in c:\Users\Administrator\Documents\Visual Studio 2012\Projects\AlumCloud\AlumCloudPlans\PlanManager.cs:line 583 --- End of stack trace from previous location where exception was thrown --- at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) at System.Runtime.CompilerServices.TaskAwaiter`1.GetResult() at AlumCloud.Controllers.Drawings.RollupController.<Get>d__0.MoveNext() in c:\Users\Administrator\Documents\Visual Studio 2012\Projects\AlumCloud\AlumCloud\Controllers\Drawings\RollupController.cs:line 39
</StackTrace>
</Error>
-------------- GetDrawingAsync ------------------------- GetDrawingAsync处理此对象属性并构建位图内容容器。处理完所有属性后，此对象可以具有1-n个位图容器，这些容器在继承的基类中处理。每个位图容器都绘制在一个大位图上。
public async Task<Bitmap> GetDrawingAsync(bool forTotals = false)
{
PartsProcessor.IGroupedParts parts = await this.ProcessedParts.GroupParts(PartsProcessor.GroupOption.CutSheet);
List<Bitmap> containers = new List<Bitmap>();
Bitmap resDraw = null;
int totalHeight = 0,
outHeight = 0;
if (parts.Doors != null)
{
if (parts.Doors.Count() > 0)
{
containers.Add(ContentContainers.GetContentContainer(parts.Doors.ToList(), ContainerType.CutSheet, Resources.Title_Doors, out outHeight));
totalHeight += outHeight;
};
}
if (parts.Leafs != null)
{
if (parts.Leafs.Count() > 0)
{
containers.Add(ContentContainers.GetContentContainer(parts.Leafs.ToList(), ContainerType.CutSheet, Resources.Title_Leafs, out outHeight));
totalHeight += outHeight;
};
}
//....many lines of code ommitted for readablitly
if (forTotals)
{
resDraw = this.DrawPage(
ref containers,
totalHeight,
Resources.Header,
this.ProcessedParts.Elevation.ProjectName,
"Totals",
Resources.Footer
);
}
else
{
resDraw = this.DrawPage(
ref containers,
totalHeight,
Resources.Header,
string.Format(Resources.Project, this.Elevation.ProjectName),
string.Format(Resources.Elevation, this.Elevation.Name),
Resources.Footer
);
};
return resDraw;
}
----------------------绘图基类---------------------- ----------------- ..代码ommited
public abstract class DrawingBase
{
public Bitmap DrawPage(ref List<Bitmap> containers, int totalHeight, string header, string subHead1, string subHead2, string footer)
{
return DrawPageHelper(ref containers, totalHeight, header, subHead1, subHead2, footer);
}
public Bitmap DrawPage(ref List<Bitmap> containers, int totalHeight, string header, string subHead1, string subHead2, string footer, decimal cost)
{
return DrawPageHelper(ref containers, totalHeight, header, subHead1, subHead2, footer, cost);
}
Bitmap DrawPageHelper(ref List<Bitmap> containers, int totalHeight, string header, string subHead1, string subHead2, string footer, decimal cost = 0)
{
int cnt = containers.Count(),
prevHeight = 10,
extra = 0,
extraHeader = 0;
if (cost > 0)
{
extra = 150;
}
else if (header.ToLower().Contains("optimization"))
{
extra = 50;
extraHeader = 50;
}
totalHeight = totalHeight + (CONTAINER_SPACE * cnt) + HEADER_HEIGHT + FOOTER_HEIGHT + extra;
if (totalHeight < DrawingOptions.PAGE_HEIGHT_SIZE)
{
totalHeight = DrawingOptions.PAGE_HEIGHT_SIZE;
}
var canvas = new Bitmap(DrawingOptions.PAGE_WIDTH_SIZE, totalHeight);
canvas.SetResolution(150, 150);
short center = (short)(DrawingOptions.PAGE_WIDTH_SIZE / 2);
using (var dc = Graphics.FromImage(canvas))
{
dc.Clear(BACK_COLOR);
dc.SmoothingMode = SmoothingMode.HighQuality;
for (byte i = 0; i < cnt; i++)
{
using (var bm = containers[i])
{
dc.DrawImageUnscaled(bm, -1, prevHeight + 5 + HEADER_HEIGHT + extraHeader);
prevHeight += containers[i].Height + CONTAINER_SPACE;
};
}
using (var pen = DrawingOptions.GetDetailsPen(PenAlignment.Inset))
{
//page edge
//dc.DrawRectangle(pen, 2, 2, canvas.Width - 4, canvas.Height - 3);
//header
string txt;
System.Drawing.SizeF txtSize;
using (var brush = new SolidBrush(DrawingOptions.LINE_COLOR))
using (var sFont = DrawingOptions.GetFont(DrawingOptions.FontSize.Small))
using (var sLargerFont = DrawingOptions.GetFont(DrawingOptions.FontSize.Small_Larger))
using (var mFont = DrawingOptions.GetFont(DrawingOptions.FontSize.Medium))
using (var lFont = DrawingOptions.GetFont(DrawingOptions.FontSize.Large))
{
txt = header;//sheet type. Estimate, Cut, Parts, ect..
System.Drawing.StringFormat drawFormat = new System.Drawing.StringFormat();
drawFormat.FormatFlags = StringFormatFlags.DirectionVertical;
txtSize = dc.MeasureString(txt, sLargerFont);
dc.DrawRectangle(pen, new Rectangle(0, -1, (short)txtSize.Height + 1, (byte)txtSize.Width));
dc.DrawString(txt, sLargerFont, brush, 0, 1, drawFormat);
//
txt = subHead1;//project name
txtSize = dc.MeasureString(txt, mFont);
dc.DrawRectangle(pen, new Rectangle((short)txtSize.Height + 1, -1, (short)txtSize.Width, (byte)txtSize.Height + 1));
dc.DrawString(txt, mFont, brush, (short)txtSize.Height + 1, 1);
txt = subHead2;//elevation name
txtSize = dc.MeasureString(txt, sFont);
dc.DrawRectangle(pen, new Rectangle((short)((canvas.Width - txtSize.Width) + 5), -1, (short)txtSize.Width + 55, (byte)txtSize.Height + 1));
dc.DrawString(txt, sFont, brush, (canvas.Width - txtSize.Width + 5), 1);
//header end
//footer
txt = footer;
txtSize = dc.MeasureString(txt, sLargerFont);
dc.DrawLine(pen, 0, canvas.Height - (txtSize.Height + 5), canvas.Width, canvas.Height - (txtSize.Height + 5));
dc.DrawString(txt, sLargerFont, brush, (short)(center - (txtSize.Width / 2)), canvas.Height - txtSize.Height - 2);
if (cost > 0)
{
//FOB shipping
txt = String.Format("Tax: {0:C}", 0.00m);
txtSize = dc.MeasureString(txt, sLargerFont);
dc.DrawString(txt, sLargerFont, brush, (short)(canvas.Width - (txtSize.Width + 10)), (canvas.Height - ((txtSize.Height * 3) + 15)) - 50);
//FOB shipping
txt = String.Format("FOB: {0:C}", 0.00m);
txtSize = dc.MeasureString(txt, sLargerFont);
dc.DrawString(txt, sLargerFont, brush, (short)(canvas.Width - (txtSize.Width + 10)), (canvas.Height - ((txtSize.Height * 2) + 10)) - 50);
//total cost
txt = String.Format("Total Cost: {0:C}", cost);
txtSize = dc.MeasureString(txt, sLargerFont);
dc.DrawString(txt, sLargerFont, brush, (short)(canvas.Width - txtSize.Width), (canvas.Height - txtSize.Height - 2) - 50);
}
}
}
}
return canvas;
}
我需要做些什么来解决这个错误？