Java.IO.File oFile = new Java.IO.File(AppPara.sAppSetupPath+ "/" +
AppPara.sAppPackage);
if (oFile.Exists())
{
   if (Build.VERSION.SdkInt >= Android.OS.BuildVersionCodes.N)
  {
   **Android.Net.Uri apkUri = FileProvider.GetUriForFile(activity,
   "StartNetApp.Android.fileprovider", oFile);**//this line show that
    error!!

   Intent oIntent = new Intent(Intent.ActionInstallPackage);
    oIntent.SetData(apkUri);
   oIntent.SetFlags(ActivityFlags.GrantReadUriPermission);
   activity.StartActivity(oIntent);
   }
}

<application android:icon="@drawable/Icon">
<provider
 android:name="android.support.v4.content.FileProvider"
 android:authorities="StartNetApp.Android.fileprovider"
 android:enabled="false"
 android:grantUriPermissions="true" >
 <meta-data
            android:name="android.support.FILE_PROVIDER_PATHS"
            android:resource="@xml/file_provider_path" />
    </provider>

 </application>

<?xml version="1.0" encoding="utf-8"?>
<paths xmlns:android="http://schemas.android.com/apk/res/android">
  <external-path   name="external_files"    path="." />
  <root-path   name="external_files"    path="/storage/"/>
</paths>