API Change: Attach ImageViewer to Plugin after init.

Plugin is now added to the viewer using an inplace add on the viewer instead of on initialization of the plugin. This change means that operations requiring the viewer must be delayed until attach operation.

skimage/viewer/plugins/base.py

@@ -1,4 +1,5 @@
 from PyQt4 import QtGui
+from PyQt4.QtCore import Qt
 
 import matplotlib as mpl
 
@@ -23,17 +24,13 @@ class Plugin(QtGui.QDialog):
     ----------
     image_viewer : ImageViewer
         Window containing image used in measurement.
-    image : array
-        Image used in measurement/manipulation.
     """
     name = 'Plugin'
     draws_on_image = False
 
-    def __init__(self, image_viewer, image_filter=None, height=100, width=400,
-                 useblit=None):
-        self.image_viewer = image_viewer
-        QtGui.QDialog.__init__(self, image_viewer)
-        self.image_viewer.plugins.append(self)
+    def __init__(self, image_filter=None, height=100, width=400, useblit=None):
+        QtGui.QDialog.__init__(self)
+        self.image_viewer = None
 
         self.setWindowTitle(self.name)
         self.layout = QtGui.QGridLayout(self)
@@ -42,18 +39,24 @@ class Plugin(QtGui.QDialog):
         if image_filter is not None:
             self.image_filter = image_filter
 
-        #TODO: Always passing image as first argument may be bad assumption.
-        self.arguments = [image_viewer.original_image]
+        self.arguments = []
         self.keyword_arguments= {}
 
-        self.image = self.image_viewer.image
-
         if useblit is None:
             useblit = True if mpl.backends.backend.endswith('Agg') else False
         self.useblit = useblit
         self.cids = []
         self.artists = []
 
+    def attach(self, image_viewer):
+        self.setParent(image_viewer)
+        self.setWindowFlags(Qt.Dialog)
+
+        self.image_viewer = image_viewer
+        self.image_viewer.plugins.append(self)
+        #TODO: Always passing image as first argument may be bad assumption.
+        self.arguments.append(self.image_viewer.original_image)
+
         if self.draws_on_image:
             self.connect_event('draw_event', self.on_draw)