如何在不使用构造函数的情况下在C＃中的另一个类中使用类的方法

Question

我在Mono上使用Libbcm2835.Net库@https://github.com/frankhommers/LibBcm2835.Net。我需要调用该库给出了Bcm2835类的方法：

using System; 
using System.Runtime.InteropServices; 

namespace LibBcm2835.Net 
{ 
    public sealed partial class Bcm2835 
    { 
//please note: I added the constructor below and tried to use it to 
//instantiate the object to be used in ADS1256.cs, but to no avail. I tried: 
// Bcm2835 bcm2835 = new Bcm2835(1); And then invoking methods from bcm2835. 
//But that gives me "An object reference is needed to access the non-static 
//member ADS1256.bcm2835" 
    public Bcm2835(int a) { } 
    ....all the methods here-on being non-static... 
    } 
} 
` 

我现在想在另一个类ADS1256.cs如下使用此：

using System; 
using LibBcm2835.Net; 
namespace ForceSeer2 
{ 
    public class ADS1256 
    {  

     public ADS1256() 
     { 
     } 


     static Bcm2835 instance; 
     public static Bcm2835 Instance { 
      get { return instance;} 
     } 
     //example of a method in this class that uses a method from the class 
     //Bcm2835: 
     public static int initializeSPI() 
      { 
       //if i had done Bcm2835 bcm2835 = new Bcm2835(1); at the top, 
      //i would now do : if (bcm2835.bcm2835_init()==0) instead of 
       //the upcoming line, leading then to the error: "An object 
      //reference is needed to access the non-static 
      //member ADS1256.bcm2835" 
       if (Instance.bcm2835_init()==0) 
        return -1; 
       else { 
        Instance.bcm2835_spi_begin(); 
        Instance.bcm2835_spi_setBitOrder ((byte)Bcm2835.bcm2835SPIBitOrder.BCM2835_SPI_BIT_ORDER_LSBFIRST); 
        Instance.bcm2835_spi_setDataMode ((byte)Bcm2835.bcm2835SPIMode.BCM2835_SPI_MODE1); //whats this about?? 
        Instance.bcm2835_spi_setClockDivider ((ushort)Bcm2835.bcm2835SPIClockDivider.BCM2835_SPI_CLOCK_DIVIDER_256);//whats this about?? 
        Instance.bcm2835_gpio_fsel ((byte)SPICS, (byte)Bcm2835.bcm2835FunctionSelect.BCM2835_GPIO_FSEL_OUTP);//whats this about?? 
        Instance.bcm2835_gpio_set ((byte)SPICS);//sets SPICS to HIGH 
        Instance.bcm2835_gpio_fsel ((byte)DRDY, (byte)Bcm2835.bcm2835FunctionSelect.BCM2835_GPIO_FSEL_INPT);//whats this about?? 
        Instance.bcm2835_gpio_set_pud ((byte)DRDY, (byte)Bcm2835.bcm2835PUDControl.BCM2835_GPIO_PUD_UP); //whats this about?? 


        return 1; 
       } 
      } 

这种使用给我的NullReferencePointer异常在线：

if (Instance.bcm2835_init()==0) 

是什么原因造成的？我该如何纠正它？

Answer 1

你应该调用bcm2835_Init方法之前添加以下代码：

// Blinks on RPi Plug P1 pin 7 (which is GPIO 4) 
const Byte pin = (byte)Bcm2835.RPiGPIOPin.RPI_V2_GPIO_P1_07; 

// Will extract (from embedded resource) and compile the library 
// if it doesn't exist in the same directory as LibBcm2835.dll. 
Bcm2835.ExtractAndCompileLibraryIfNotExists(); 

// Grabbing the instance will dynamically load the libbcm2835.so 
// library, so make sure it's there before accessing this property. 
Bcm2835 bcm2835 = Bcm2835.Instance; 

Answer 2

看来，你可以使用Singleton设计模式：

using System; 
using LibBcm2835.Net; 
namespace ForceSeer2 
{ 
    public class ADS1256 
    {  
     public ADS1256() 
     { 
     } 

     private static Bcm2835 instance; 
     private static object syncRoot = new Object(); 

     public static Bcm2835 Instance 
     { 
      get 
      { 
       if(instance == null) 
       { 
        lock(syncRoot) 
        { 
         if(instance == null) 
          instance = new Bcm2835(); 
        } 
       } 

       return instance; 
      } 
     } 

     //example of a method in this class that uses a method from the class 
     //Bcm2835: 
     public static int initializeSPI() 
     { 
      //Your method implementation here 
     } 

     //Other class members here 
    } 
}