Xamarin Java.Lang.Object创建效率低下

Question

I need to generate a large list of objects for a ListView / GridView. From what I understand, these objects must derive from Java.Lang.Object. The time it takes to generate these objects is significant.

I created a simple test to see how long it takes to simply create 5000 objects that derive from Java.Lang.Object and compared it to creating 5000 objects that derive from System.Object.

public class MyJavaObject : Java.Lang.Object { }    
public class MyObject : System.Object { }

private void CreateObjects()
{
    var objectCount = 5000;

    var javaObjectsWatch = new Stopwatch();
    javaObjectsWatch.Start();
    for (int i = 0; i < objectCount; i++)
    {
        new MyJavaObject();
    }
    javaObjectsWatch.Stop();
    var javaObjectsCreationElapsed = javaObjectsWatch.Elapsed.TotalMilliseconds;
    Console.WriteLine($"{objectCount} java objects took {javaObjectsCreationElapsed} milliseconds");

    var objectsWatch = new Stopwatch();
    objectsWatch.Start();
    for (int i = 0; i < objectCount; i++)
    {
        new MyObject();
    }
    objectsWatch.Stop();
    var objectsCreationElapsed = objectsWatch.Elapsed.TotalMilliseconds;
    Console.WriteLine($"{objectCount} objects took {objectsCreationElapsed} milliseconds");
}

Running CreateObjects results in the following being written to console.

"5000 java objects took 4437.1033 milliseconds"

"5000 objects took 1.831 milliseconds"

It takes almost 4.5 seconds to create the MyJavaObjects, and not even a hundredth of a second for the MyObjects.

How can I get the creation of the MyJavaObjects to be closer to the efficiency of creating MyObjects?

Answer 1

The creation of a Java object contains the parts: 1) the object is created on Dalvik VM; 2) a corresponding object created on Xamarin.Android VM to track the lifecycle of the other object. Quite similar to .NET/COM inter-operation.

Thus, it won't be as quick as you wished, but still fast enough for most of the mobile apps. It is a burden the solution must pay when it needs to use a set of specific components. For other scenarios, Xamarin.Android can directly call into Android native API without touching Dalvik.

Some of the internals can be found at Miguel de Icaza's blog on Mono for Android.