feat: Allows registering the onRequestPermissionsResult callback.

Adds an interface in PythonActivity and a method to register a
Python function which will be called when the
onRequestPermissionsResult callback is received.
In android/permissions.py, a new function
'register_permissions_callback' is added to register a Python
function (that takes three arguments) which will receive the
three arguments of onRequestPermissionsResult.

pythonforandroid/bootstraps/sdl2/build/src/main/java/org/kivy/android/PythonActivity.java

@@ -581,7 +581,34 @@ public void onWindowFocusChanged(boolean hasFocus) {
             // call native function (since it's not yet loaded)
         }
         considerLoadingScreenRemoval();
-    }    
+    }
+
+    /**
+     * Used by android.permissions p4a module to register a call back after
+     * requesting runtime permissions
+     **/
+    public interface PermissionsCallback {
+        void onRequestPermissionsResult(int requestCode, String[] permissions, int[] grantResults);
+    }
+
+    private PermissionsCallback permissionCallback;
+    private boolean havePermissionsCallback = false;
+
+    public void addPermissionsCallback(PermissionsCallback callback) {
+        permissionCallback = callback;
+        havePermissionsCallback = true;
+        Log.v(TAG, "addPermissionsCallback(): Added callback for onRequestPermissionsResult");
+    }
+
+    @Override
+    public void onRequestPermissionsResult(int requestCode, String[] permissions, int[] grantResults) {
+        Log.v(TAG, "onRequestPermissionsResult()");
+        if (havePermissionsCallback) {
+            Log.v(TAG, "onRequestPermissionsResult passed to callback");
+            permissionCallback.onRequestPermissionsResult(requestCode, permissions, grantResults);
+        }
+        super.onRequestPermissionsResult(requestCode, permissions, grantResults);
+    }
 
     /**
      * Used by android.permissions p4a module to check a permission
@@ -592,9 +619,9 @@ public boolean checkCurrentPermission(String permission) {
 
         try {
             java.lang.reflect.Method methodCheckPermission =
-                Activity.class.getMethod("checkSelfPermission", java.lang.String.class);  
+                Activity.class.getMethod("checkSelfPermission", java.lang.String.class);
             Object resultObj = methodCheckPermission.invoke(this, permission);
-            int result = Integer.parseInt(resultObj.toString());   
+            int result = Integer.parseInt(resultObj.toString());
             if (result == PackageManager.PERMISSION_GRANTED) 
                 return true;
         } catch (IllegalAccessException | NoSuchMethodException |
@@ -612,7 +639,7 @@ public void requestPermissions(String[] permissions) {
         try {
             java.lang.reflect.Method methodRequestPermission =
                 Activity.class.getMethod("requestPermissions",
-                java.lang.String[].class, int.class);  
+                java.lang.String[].class, int.class);
             methodRequestPermission.invoke(this, permissions, 1);
         } catch (IllegalAccessException | NoSuchMethodException |
                  InvocationTargetException e) {

pythonforandroid/recipes/android/src/android/permissions.py

@@ -1,6 +1,6 @@
 
 try:
-    from jnius import autoclass
+    from jnius import autoclass, PythonJavaClass, java_method
 except ImportError:
     # To allow importing by build/manifest-creating code without
     # pyjnius being present:
@@ -422,6 +422,41 @@ class Permission:
         )
 
 
+class onRequestPermissionsCallback(PythonJavaClass):
+    """Callback class for registering a Python callback from
+    onRequestPermissionsResult in PythonActivity.
+    """
+    __javainterfaces__ = ['org.kivy.android.PythonActivity$PermissionsCallback']
+    __javacontext__ = 'app'
+    _callback = None  # To avoid garbage collection
+
+    def __init__(self, func):
+        self.func = func
+        onRequestPermissionsCallback._callback = self
+        super().__init__()
+
+    @java_method('(I[Ljava/lang/String;[I)V')
+    def onRequestPermissionsResult(self, requestCode, permissions, grantResults):
+        self.func(requestCode, permissions, grantResults)
+
+
+def register_permissions_callback(callback):
+    """Register a callback. This will asynchronously receive arguments from
+    onRequestPermissionsResult on PythonActivity after request_permission(s)
+    is called.
+
+    The callback must accept three arguments: requestCode, permissions and
+    grantResults.
+
+    Note that calling request_permission on SDK_INT < 23 will return
+    immediately (as run-time permissions are not required), and so this
+    callback will never happen.
+    """
+    java_callback = onRequestPermissionsCallback(callback)
+    python_activity = autoclass('org.kivy.android.PythonActivity')
+    python_activity.addPermissionsCallback(java_callback)
+
+
 def request_permissions(permissions):
     python_activity = autoclass('org.kivy.android.PythonActivity')
     python_activity.requestPermissions(permissions)