SelectStorageLocationActivity handles read-only/temporary cases (first implementation, untested)

src/Kp2aBusinessLogic/Io/AndroidContentStorage.cs

@@ -143,6 +143,18 @@ namespace keepass2android.Io
 		{
 			throw new NotImplementedException();
 		}
+
+		public bool IsPermanentLocation(IOConnectionInfo ioc)
+		{
+			//on pre-Kitkat devices, content:// is always temporary:
+			return false;
+		}
+
+		public bool IsReadOnly(IOConnectionInfo ioc)
+		{
+			//on pre-Kitkat devices, we can't write content:// files
+			return true;
+		}
 	}
 
 	class AndroidContentWriteTransaction : IWriteTransaction

src/Kp2aBusinessLogic/Io/BuiltInFileStorage.cs

@@ -4,6 +4,7 @@ using System.Globalization;
 using System.IO;
 using System.Net;
 using System.Net.Security;
+using System.Security;
 using Android.Content;
 using Android.OS;
 using Java.Security.Cert;
@@ -290,5 +291,67 @@ namespace keepass2android.Io
 			res.Path += filename;
 			return res;
 		}
+
+		public bool IsPermanentLocation(IOConnectionInfo ioc)
+		{
+			return true;
+		}
+
+		public bool IsReadOnlyBecauseKitkatRestrictions(IOConnectionInfo ioc)
+		{
+			if (IsLocalFileFlaggedReadOnly(ioc))
+				return false; //it's not read-only because of the restrictions introduced in kitkat
+			try
+			{
+				//test if we can open 
+				//http://www.doubleencore.com/2014/03/android-external-storage/#comment-1294469517
+				using (var writer = new Java.IO.FileOutputStream(ioc.Path, true))
+				{
+					writer.Close();
+					return false; //we can write
+				}
+			}
+			catch (Java.IO.IOException)
+			{
+				//seems like we can't write to that location even though it's not read-only
+				return true;
+			}
+			
+		}
+
+		public bool IsReadOnly(IOConnectionInfo ioc)
+		{
+			if (ioc.IsLocalFile())
+			{
+				if (IsLocalFileFlaggedReadOnly(ioc))
+					return true;
+				if (IsReadOnlyBecauseKitkatRestrictions(ioc))
+					return true;
+
+				return false;
+			}
+			//for remote files assume they can be written: (think positive! :-) )
+			return false;
+		}
+
+		private bool IsLocalFileFlaggedReadOnly(IOConnectionInfo ioc)
+		{
+			try
+			{
+				return new FileInfo(ioc.Path).IsReadOnly;
+			}
+			catch (SecurityException)
+			{
+				return true;
+			}
+			catch (UnauthorizedAccessException)
+			{
+				return true;
+			}
+			catch (Exception)
+			{
+				return false;
+			}
+		}
 	}
 }

src/Kp2aBusinessLogic/Io/CachingFileStorage.cs

@@ -542,6 +542,19 @@ namespace keepass2android.Io
 			
 		}
 
+		public bool IsPermanentLocation(IOConnectionInfo ioc)
+		{
+			//even though the cache would be permanent, it's not a good idea to cache a temporary file, so return false in that case:
+			return _cachedStorage.IsPermanentLocation(ioc);
+		}
+
+		public bool IsReadOnly(IOConnectionInfo ioc)
+		{
+			//even though the cache can always be written, the changes made in the cache could not be transferred to the cached file
+			//so we better treat the cache as read-only as well.
+			return _cachedStorage.IsReadOnly(ioc);
+		}
+
 		private void StoreFilePath(IOConnectionInfo folderPath, string filename, IOConnectionInfo res)
 		{
 			File.WriteAllText(CachedFilePath(GetPseudoIoc(folderPath, filename)) + ".filepath", res.Path);

src/Kp2aBusinessLogic/Io/IFileStorage.cs

@@ -149,6 +149,17 @@ namespace keepass2android.Io
 		/// </summary>
 		/// The method may throw FileNotFoundException or not in case the file doesn't exist.
 		IOConnectionInfo GetFilePath(IOConnectionInfo folderPath, string filename);
+
+		/// <summary>
+		/// returns true if it can be expected that this location will be available permanently (in contrast to a cache copy or temporary URI permissions in Android)
+		/// </summary>
+		/// Does not require to exist forever!
+		bool IsPermanentLocation(IOConnectionInfo ioc);
+
+		/// <summary>
+		/// Should return true if the file cannot be written.
+		/// </summary>
+		bool IsReadOnly(IOConnectionInfo ioc);
 	}
 
 	public interface IWriteTransaction: IDisposable

src/Kp2aBusinessLogic/Kp2aBusinessLogic.csproj

@@ -20,7 +20,7 @@
     <DebugType>full</DebugType>
     <Optimize>false</Optimize>
     <OutputPath>bin\Debug\</OutputPath>
-    <DefineConstants>TRACE;DEBUG;EXCLUDE_TWOFISH;EXCLUDE_KEYBOARD;EXCLUDE_FILECHOOSER;EXCLUDE_JAVAFILESTORAGE;INCLUDE_KEYTRANSFORM</DefineConstants>
+    <DefineConstants>TRACE;DEBUG;EXCLUDE_TWOFISH;EXCLUDE_KEYBOARD;INCLUDE_FILECHOOSER;EXCLUDE_JAVAFILESTORAGE;INCLUDE_KEYTRANSFORM</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>