Accessing Java Classes from Mono for Android via JNI

Mono for Android let’s you write Android applications in a .NET language (for example, C#). It comes with wrappers for almost the entire Android API so building “standard” apps is easy enough. However, sometimes you may need to work with third party Java classes that aren’t part of Android itself. These classes usually come as a .jar file. Fortunately, Mono for Android provides a way to access those Java classes. Unfortunately, this way is a “little” bit tricky and documentation on this is (currently) quite limited.

This article will show some basic example of how to call a method of a Java class from Mono for Android. We will use Visual Studio 2010 in this article, as it is (in my opinion) currently superior to Mono Develop.

Update: Mono for Android v4.2 and higher provides an automatic way for doing the things described in this article. This is a lot easier than the manual way and thus the preferred way.

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Calculate return value for sort by int

Most programming languages (such as C#, Java, …) allow you to sort lists. Most of them also allow you to specify a sorting function so that you can customize the sort order. These functions usually take parameters a and b and define the return value as follows:

Return value if
less than zero a is less than b
equals zero a is equal to b
greater than zero a is greater than b

Usually you would do something like this (code in C#):

int Compare(int a, int b) {
  if (a < b) {
    return -1;
  else if (a > b) {
    return 1;
  else {
    return 0;

However, when comparing int values, there’s a much quicker way to do this:

int Compare(int a, int b) {
  return a - b;

That’s it.

Note: Care should be taken if a and/or b can come close to int.MaxValue or int.MinValue. In this case the results may not be what one wants (like if a = int.MinValue and b = 1 then the result will be int.MaxValue which is wrong obviously).

Bug of the day: Broken renaming in ReSharper

In my opinion, refactoring is the way to keep a software project clean. So, it’s good to have tools that support the refactoring process.

ReSharper is such a tool. It provides refactoring capabilities for C#/Visual Studio.

Unfortunately, the renaming code in ReSharper currently (version 7.1.1) contains a bug. This bug may prevent ReSharper from renaming all occurrences of a certain symbol.

The following code exhibits this problem:

using System;
public class SomeOtherClass {
  public string GetString(int col) {
    return null;
public class MyClass {
  public void YouCantRenameMe() { }
  public void ThisFunctionBreaksTheRenaming() {
    // The following line breaks the renaming.
    SomeFunction((row) => row.GetString(0));
  public void SomeFunction<T>(Func<SomeOtherClass, T> func) {

If you try to rename the method YouCantRenameMe() (in line 10), ReSharper won’t rename the method call in line 18.

The problem is the code in method ThisFunctionBreaksTheRenaming() which somehow breaks the renaming process.

Update: This bug is not present in version 7.1. So, for now, I’ve downgraded to this version.

WCF: Real Easy

If you search for WCF tutorials, you’ll find a lot of elaborate examples that involve editing several files.

This tutorial is (supposed to be) different. It uses the simple most approach I could find for using WCF. It’ll only involve one file and no XML descriptors (read: app.config).

I’ll explain how to use WCF for communicating between .NET processes and how to use it for HTTP requests.

The initial code is based primarily on this nice tutorial.

Let’s get started.

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C++/CLI Cheat Sheet

This article provides a quick comparison between C++/CLI and C#. It’s meant for those who know C# (and possibly C++) and will explain which C++/CLI language construct correspond with which in C#. (I don’t know Visual Basic so I can’t add infos about this here.)

Note: This is not a complete reference but rather quick reference for those features that are (in my opinion) the most unclear.

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