Windows IoT 核心读取值返回 System.Threading.Tasks.Task`1[System.Single] 而不是浮点数

Question

我正在关注 Chris Pietschmann 的 Raspberry Pi 气象站 3.0 教程，使用 BME280 传感器：https://www.hackster.io/23021/weather-station-v-3-0-b8b8bc。

在 MainPage 中，他调用 ReadTemperture（或传感器的任何其他寄存器）来写出 returned 值。

我在 Debug.Writeline() 中得到 System.Threading.Tasks.Task`1[System.Single] 的所有值...温度、湿度、压力和高度。

我在方法中添加了一个写入行，我得到了正确的值，所以我正在从传感器读取...我只是不能 return 它返回到主页并读取它。

看起来我在异步方面遗漏了什么？

这是主页：

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.IO;
using System.Linq;
using System.Runtime.InteropServices.WindowsRuntime;
using System.Threading.Tasks;
using Windows.Foundation;
using Windows.Foundation.Collections;
using Windows.UI.Xaml;
using Windows.UI.Xaml.Controls;
using Windows.UI.Xaml.Controls.Primitives;
using Windows.UI.Xaml.Data;
using Windows.UI.Xaml.Input;
using Windows.UI.Xaml.Media;
using Windows.UI.Xaml.Navigation;

// The Blank Page item template is documented at http://go.microsoft.com/fwlink/?LinkId=402352&clcid=0x409

namespace IoT_BME280_Temp
{
    /// <summary>
    /// An empty page that can be used on its own or navigated to within a Frame.
    /// </summary>
    public sealed partial class MainPage : Page
    {
        DispatcherTimer _timer;


        const float seaLevelPressure = 1026.00f;  //was 1022.00
        BME280Sensor _bme280 = new BME280Sensor();

        public MainPage()

        {
            this.InitializeComponent();
        }

        protected override async void OnNavigatedTo(NavigationEventArgs e)
        {
            base.OnNavigatedTo(e);


            await _bme280.Initialize();

            _timer = new DispatcherTimer();
            _timer.Interval = TimeSpan.FromSeconds(5);
            _timer.Tick += _timer_Tick;

            _timer.Start();

        }

        private void _timer_Tick(object sender, object e)
        {
            try
            {
                var temp     = _bme280.ReadTemperature();
                Debug.WriteLine("Temp: {0} deg C", temp);  // Results in: Temp: System.Threading.Tasks.Task`1[System.Single] deg C
                var humidity = _bme280.ReadHumidity();
                var pressure = _bme280.ReadPressure();
                var altitude = _bme280.ReadAltitude(seaLevelPressure);
            } 
        catch
            {
                Debug.WriteLine("Cannot read values from sensor...");
        }
        }
    }
}

这是来自 BME280Sensor class 的 ReadTemprature()：

public async Task<float> ReadTemperature()
    {
        //Make sure the I2C device is initialized
        if (!init) await Begin();

        //Read the MSB, LSB and bits 7:4 (XLSB) of the temperature from the BME280 registers
        byte tmsb = ReadByte((byte)eRegisters.BME280_REGISTER_TEMPDATA_MSB);
        byte tlsb = ReadByte((byte)eRegisters.BME280_REGISTER_TEMPDATA_LSB);
        byte txlsb = ReadByte((byte)eRegisters.BME280_REGISTER_TEMPDATA_XLSB); // bits 7:4

        //Combine the values into a 32-bit integer
        Int32 t = (tmsb << 12) + (tlsb << 4) + (txlsb >> 4);

        //Convert the raw value to the temperature in degC
        double temp = BME280_compensate_T_double(t);
        Debug.WriteLine("Temp: {0} deg C", temp);  //  This results in the correct temperature value...

        //Return the temperature as a float value
        return (float)temp;
    }

提前致谢！

Answer 1

你会得到一个 Task 因为这就是你同步调用它时 ReadTemperature returns 的结果。要获得任务的结果而不是任务本身，您需要使用 await 调用方法并将 _timer_Tick 也更改为 async：

private async void _timer_Tick(object sender, object e)
{
    try
    {
        var temp     = await _bme280.ReadTemperature();
        Debug.WriteLine("Temp: {0} deg C", temp);
        var humidity = _bme280.ReadHumidity();
        var pressure = _bme280.ReadPressure();
        var altitude = _bme280.ReadAltitude(seaLevelPressure);
    } 
    catch
    {
        Debug.WriteLine("Cannot read values from sensor...");
    }
}

Windows IoT 核心读取值返回 System.Threading.Tasks.Task`1[System.Single] 而不是浮点数

Windows IoT Core reading value returned System.Threading.Tasks.Task`1[System.Single] instead of float

c#

async-await

raspberry-pi2

windowsiot