c# 将一个长耗时任务改成task

public Task<ObservableCollection<WaterFallDataSource2>> InitalrenderSourceandBrush2(int width)
        {
            Stopwatch w = new Stopwatch();
            w.Start();
            points3.Clear();
            int wavelength = GlobalStorage.BigWaves.Length;
            int allRows = wavelength / width;
            w.Stop();
            Debug.WriteLine("w.ElapsedMilliseconds:" + w.ElapsedMilliseconds);
            Debug.WriteLine("allRows:" + allRows);
            if (allRows > 0)
            {
                Parallel.For(0, _pagesize, (lk) =>
                {
                    ObservableCollection<DataPoint3> dataPoints = new ObservableCollection<DataPoint3>();
                    for (byte j = 0; j < 150; j++)
                    {
                        for (short i = 0; i < width; i++)
                        {
                            DataPoint3 dataPoint = new DataPoint3() { VariableX = i, VariableY = j };
                            dataPoint.Type = GetColorIndex2(GlobalStorage.BigWaves[lk * width + i][j]);
                            dataPoints.Add(dataPoint);
                        }
                    }
                    WaterFallDataSource2 waterFallDataSource = new WaterFallDataSource2();
                    waterFallDataSource.DataPoints = dataPoints;
                    waterFallDataSource.BrushInfo = brushes;
                    waterFallDataSource.Index = lk;
                    waterFallDataSource.Width = width;
                    waterFallDataSource.StartTime = BeatWaveDataConversionExtension.WaveDotToDateTime(BeatInfoCache.BeatInfos.ElementAt(lk * width).R).ToString();
                    points3.Add(waterFallDataSource);
                });
                return Task.FromResult<ObservableCollection<WaterFallDataSource2>>(points3.OrderBy(p => p.Index).ToObservableCollection<WaterFallDataSource2>());
            }
            else
            {
                ObservableCollection<DataPoint3> dataPoints = new ObservableCollection<DataPoint3>();
                WaterFallDataSource2 waterFallDataSource = new WaterFallDataSource2();
                for (byte j = 0; j < 150; j++)
                {
                    for (short i = 0; i < wavelength; i++)
                    {
                        short value = GlobalStorage.BigWaves[i][j];
                        DataPoint3 dataPoint = new DataPoint3() { VariableX = i, VariableY = j };
                        dataPoint.Type = GetColorIndex2(value);
                        dataPoints.Add(dataPoint);
                    }
                }
                waterFallDataSource.DataPoints = dataPoints;
                waterFallDataSource.BrushInfo = brushes;
                waterFallDataSource.Index = 0;
                waterFallDataSource.Width = width;
                points3.Add(waterFallDataSource);
                return Task.FromResult<ObservableCollection<WaterFallDataSource2>>(points3);
            }
        }

调用 

 var reuslt = await _stTrendController.InitalrenderSourceandBrush2((int)firstrowgrid.ActualWidth - 27);