Type cast from Java.Lang.Object to native CLR type in MonoDroid

Question

How to cast Java.Lang.Object to some native type?

Example:

ListView adapter contains instances of native type Message. When i am trying to get SelectedItem from

Answer 1

You could always try the JavaCast<> method (most of the views implement this)(not tested):

var message = list.SelectedItem.JavaCast< Message >();

Answer 2

All of the above answers are correct but I found the simplest way for my case was to make the object a subclass of Java.Lang.Object.

For example I'm writing a Android app in Monotouch, mimicking the concept of a UITableView in iOS using the ExpandableListAdapter, which requires the equivalent of UITableViewCells, so I subclassed cell objects from Java.Lang.Object allowing me to implement a subclass of ExpandableListAdapter such as

public override Java.Lang.Object GetChild(int position, int childPosition)

Etc.

Answer 3

If for some reason GetChildAtPosition is not possible, serialise the object to json string and then deserialise the string back to native class.

Answer 4

The least magical way of getting a native type from the Spinner is to call

    message = ((ArrayAdapter<Message>)list.Adapter).GetItem(list.SelectedItemPosition);

Answer 5

After long time debuging, have found the solution:

public static class ObjectTypeHelper
{
    public static T Cast<T>(this Java.Lang.Object obj) where T : class
    {
        var propertyInfo = obj.GetType().GetProperty("Instance");
        return propertyInfo == null ? null : propertyInfo.GetValue(obj, null) as T;
    }
}

Usage example:

 var message = list.GetItemAtPosition(e.Position).Cast<Message>();
 bundle.PutInt("Message", message.ID);

After careful sdk study have found MonoDroid integrated extension for this purpose:

public static TResult JavaCast<TResult>(this Android.Runtime.IJavaObject instance)
where TResult : class, Android.Runtime.IJavaObject
Member of Android.Runtime.Extensions

Answer 6

For generic collections, the right answer would be to use JavaList, which is a Java.Lang.Object and also implements IList. But it involves more work that's for sure. This is actually just an adapter for Java's ArrayList implementation.