Weird behaviour of AndroidJavaObject in Unity, when implemented through C# - unity3d

Question

Rather long post follows. It's fairly complex, needs someone who has worked with Unity Plugins before (creating them, not using them) and I'm not looking to get downvoted because a few common search terms show up. So, please read the entire post.
So, I've been having a rather weird issue happening when I try to call native functions through Unity's AndroidJavaObject
I've built native plugins in the past before, I'm trying to remove my dependancies on having to update multiple JARs each time I need to update my plugins. So, I'm moving a lot of my native Java code from plugins, into Unity itself.
Specifically, there's a way to call native Android functions (i.e. system functions) straight from C#, rather than creating a plugin and calling a function in the plugin that invokes the native function.
For example, earlier, if I had to create a Toast, I'd have to write some native code in Java, export the plugin and then call the function. These days, one can just call the Toast.makeText straight from C# as follows.
Here's how I make the call for a Toast.
public static void Toast (string text, int duration) {
#if UNITY_ANDROID && !UNITY_EDITOR
CreateActivity();
activity.Call("runOnUiThread", new AndroidJavaRunnable ( () => {
new AndroidJavaObject("android.widget.Toast", activity)
.CallStatic<AndroidJavaObject>("makeText", activity, text, duration)
.Call("show");
}) );
#endif
}
and here's the CreateActivity method
private static void CreateActivity () {
#if UNITY_ANDROID && !UNITY_EDITOR
if(activity == null)
activity = new AndroidJavaClass("com.unity3d.player.UnityPlayer").
GetStatic<AndroidJavaObject>("currentActivity");
#endif
}
This works perfectly. However, when I try the same approach for creating an AlertDialog, I get an androidjavaexception java.lang.classnotfoundexception
Here's the relevant code
public static void ShowAlert (string title, string message, string buttonText) {
#if UNITY_ANDROID && !UNITY_EDITOR
CreateActivity();
activity.Call("runOnUiThread", new AndroidJavaRunnable ( () => {
var builder = new AndroidJavaObject("android.app.AlertDialog.Builder", activity);
***//Exception happens in the above line***
builder.Call<AndroidJavaObject>("setMessage", message)
.Call<AndroidJavaObject>("setTitle", title)
.Call<AndroidJavaObject>("setCancelable", false)
.Call<AndroidJavaObject>("setNeutralButton", buttonText)
.Call("show");
}) );
#endif
}
What I've tried
Used android.support.v7.app.AlertDialog.Builder instead of android.app.AlertDialog.Builder
Added the support JARs for v7 & v4 (Specifically android-support-v4 & android-support-v7-appcompat)
Tried creating my own implementation for Unity's JNI and invoking that
All the above failed. (The third one, rather spectacularly)
Now, I tried other classes as well, and most of them work (such as ProgressDialog, which is a subclass of AlertDialog), and those work!
At this point, I'm rather stumped and I can't think of a VALID reason for certain functions to work, and the others to fail.
Any thoughts are appreciated.
EDIT 1: Added LogCat
I/Unity: AndroidJavaException: java.lang.ClassNotFoundException: android.app.AlertDialog.Builder
at UnityEngine.AndroidJNISafe.CheckException () [0x00000] in <filename unknown>:0
at UnityEngine.AndroidJNISafe.CallStaticObjectMethod (IntPtr clazz, IntPtr methodID, UnityEngine.jvalue[] args) [0x00000] in <filename unknown>:0
at UnityEngine.AndroidJavaObject._CallStatic[AndroidJavaObject] (System.String methodName, System.Object[] args) [0x00000] in <filename unknown>:0
at UnityEngine.AndroidJavaObject.CallStatic[AndroidJavaObject] (System.String methodName, System.Object[] args) [0x00000] in <filename unknown>:0
at UnityEngine.AndroidJavaObject.FindClass (System.String name) [0x00000] in <filename unknown>:0
at UnityEngine.AndroidJavaObject._AndroidJavaObject (System.String className, System.Object[] args) [0x00000] in <filename unknown>:0
at UnityEngine.AndroidJavaObject..ctor (System.String className, System.Object[] args) [0x00000] in <filename unknown>:0
at AndroidNative+<ShowAlert>c__AnonSto

Answer 1

The problem you are running into, is that AlertDialog.Builder is a nested class of AlertDialog, and creating nested classes through reflection (which is what AndroidJavaObject is trying to do) requires a slightly different syntax in Java:
android.app.AlertDialog$Builder
There are some other tiny mistakes in your code (that you couldn't know about because your constructor wasn't working):
setNeutralButton requires a callback argument (which can be null)
show has to be called on the AlertDialog itself, not on the builder.
Taking these tiny corrections into consideration, a working code sample looks like this:
public static void ShowAlert(string title, string message, string buttonText)
{
CreateActivity();
activity.Call("runOnUiThread", new AndroidJavaRunnable(() =>
{
var builder = new AndroidJavaObject("android.app.AlertDialog$Builder", activity);
builder.Call<AndroidJavaObject>("setMessage", message)
.Call<AndroidJavaObject>("setTitle", title)
.Call<AndroidJavaObject>("setCancelable", false)
.Call<AndroidJavaObject>("setNeutralButton", buttonText, null)
.Call<AndroidJavaObject>("create")
.Call("show");
}));
}