Unity invokes the proxy method on the Java thread that calls the interface method, which isn't always the Unity main thread. To dispatch work to the Unity main thread, use AndroidApplication.InvokeOnUnityMainThread, which blocks the calling thread until the delegate completes and has no effect in the Editor.
Android requires UI operations, such as showing a dialog, to run on the Android UI thread. The following example wraps the dialog call in runOnUiThread for that reason. You can also use AndroidApplication.InvokeOnUIThread to dispatch to that thread.
Note: this API can be used from a custom thread, but requires that thread to be attached to JVM first. Refer to AndroidJNI.AttachCurrentThread.
// Opens an android date picker dialog and grabs the result using a callback.
using UnityEngine;
using System;
class ExampleClass : MonoBehaviour
{
private static DateTime selectedDate = DateTime.Now;
class DateCallback : AndroidJavaProxy
{
public DateCallback() : base("android.app.DatePickerDialog$OnDateSetListener") {}
void onDateSet(AndroidJavaObject view, int year, int monthOfYear, int dayOfMonth)
{
selectedDate = new DateTime(year, monthOfYear + 1, dayOfMonth);
// If you have no longer any uses for the object, it must be disposed to prevent a leak
view.Dispose();
}
}
void OnGUI()
{
if (GUI.Button(new Rect(15, 15, 450, 75), string.Format("{0:yyyy-MM-dd}", selectedDate)))
{
var activity = new AndroidJavaClass("com.unity3d.player.UnityPlayer").GetStatic<AndroidJavaObject>("currentActivity");
activity.Call("runOnUiThread", new AndroidJavaRunnable(() =>
{
new AndroidJavaObject("android.app.DatePickerDialog", activity, new DateCallback(), selectedDate.Year, selectedDate.Month - 1, selectedDate.Day).Call("show");
}));
}
}
}