System.Text.Encoding与System.Runtime冲突

Question

在我将project.json更改为csproj后，我遇到了编译错误：

  

错误CS0433：类型＆＃39;编码＆＃39;存在于＆＃39; System.Text.Encoding，Version = 4.0.10.0，Culture = neutral，   公钥= b03f5f7f11d50a3a＆＃39;和＆＃39; System.Runtime，Version = 4.2.0.0，Culture = neutral，PublicKeyToken = b03f5f7f11d50a3a＆＃39;

我的csproj：

 #import "AVCamPreviewView.h"
 #import <AVFoundation/AVFoundation.h>
 #import <Photos/Photos.h>
 #import <UIKit/UIKit.h>

 @implementation AVCamPreviewView

+ (Class)layerClass
{
    return [AVCaptureVideoPreviewLayer class];
}

     - (AVCaptureSession *)session
   {
        return [(AVCaptureVideoPreviewLayer *)[self layer] session];
    }

     - (void)setSession:(AVCaptureSession *)session
    {

      [(AVCaptureVideoPreviewLayer *)[self layer] setSession: session];

     }
    @end

代码是这样的：

   #import <UIKit/UIKit.h>

 @class AVCaptureSession;

 @interface AVCamPreviewView : UIView

 @property (nonatomic,retain) AVCaptureSession *session;

 @end

有人可以帮忙吗？