You can now assign task successor and predecessors. Sweet. Thanks myoualid!

src/blenderbim/blenderbim/bim/module/sequence/__init__.py

@@ -32,6 +32,10 @@ classes = (
     operator.EnableEditingTask,
     operator.DisableEditingTask,
     operator.EditTask,
+    operator.AssignPredecessor,
+    operator.AssignSuccessor,
+    operator.UnassignPredecessor,
+    operator.UnassignSuccessor,
     prop.WorkPlan,
     prop.BIMWorkPlanProperties,
     prop.Task,

src/blenderbim/blenderbim/bim/module/sequence/operator.py

@@ -546,3 +546,75 @@ class EditTask(bpy.types.Operator):
         bpy.ops.bim.disable_editing_task()
         bpy.ops.bim.enable_editing_tasks(work_schedule=props.active_work_schedule_id)
         return {"FINISHED"}
+
+
+class AssignPredecessor(bpy.types.Operator):
+    bl_idname = "bim.assign_predecessor"
+    bl_label = "Assign Predecessor"
+    task: bpy.props.IntProperty()
+
+    def execute(self, context):
+        props = context.scene.BIMWorkScheduleProperties
+        self.file = IfcStore.get_file()
+        ifcopenshell.api.run(
+            "sequence.assign_sequence",
+            self.file,
+            relating_process=IfcStore.get_file().by_id(self.task),
+            related_process=IfcStore.get_file().by_id(props.active_task_id),
+        )
+        Data.load(self.file)
+        return {"FINISHED"}
+
+
+class AssignSuccessor(bpy.types.Operator):
+    bl_idname = "bim.assign_successor"
+    bl_label = "Assign Successor"
+    task: bpy.props.IntProperty()
+
+    def execute(self, context):
+        props = context.scene.BIMWorkScheduleProperties
+        self.file = IfcStore.get_file()
+        ifcopenshell.api.run(
+            "sequence.assign_sequence",
+            self.file,
+            relating_process=IfcStore.get_file().by_id(props.active_task_id),
+            related_process=IfcStore.get_file().by_id(self.task),
+        )
+        Data.load(self.file)
+        return {"FINISHED"}
+
+
+class UnassignPredecessor(bpy.types.Operator):
+    bl_idname = "bim.unassign_predecessor"
+    bl_label = "Unassign Predecessor"
+    task: bpy.props.IntProperty()
+
+    def execute(self, context):
+        props = context.scene.BIMWorkScheduleProperties
+        self.file = IfcStore.get_file()
+        ifcopenshell.api.run(
+            "sequence.unassign_sequence",
+            self.file,
+            relating_process=IfcStore.get_file().by_id(self.task),
+            related_process=IfcStore.get_file().by_id(props.active_task_id),
+        )
+        Data.load(self.file)
+        return {"FINISHED"}
+
+
+class UnassignSuccessor(bpy.types.Operator):
+    bl_idname = "bim.unassign_successor"
+    bl_label = "Unassign Successor"
+    task: bpy.props.IntProperty()
+
+    def execute(self, context):
+        props = context.scene.BIMWorkScheduleProperties
+        self.file = IfcStore.get_file()
+        ifcopenshell.api.run(
+            "sequence.unassign_sequence",
+            self.file,
+            relating_process=IfcStore.get_file().by_id(props.active_task_id),
+            related_process=IfcStore.get_file().by_id(self.task),
+        )
+        Data.load(self.file)
+        return {"FINISHED"}

src/blenderbim/blenderbim/bim/module/sequence/ui.py

@@ -153,6 +153,7 @@ class BIM_PT_work_schedules(Panel):
 class BIM_UL_tasks(UIList):
     def draw_item(self, context, layout, data, item, icon, active_data, active_propname):
         if item:
+            props = context.scene.BIMWorkScheduleProperties
             row = layout.row(align=True)
             for i in range(0, item.level_index):
                 row.label(text="", icon="BLANK1")
@@ -169,10 +170,20 @@ class BIM_UL_tasks(UIList):
                 row.label(text="", icon="DOT")
             row.prop(item, "identification", emboss=False, text="")
             row.prop(item, "name", emboss=False, text="")
-            if context.scene.BIMWorkScheduleProperties.active_task_id == item.ifc_definition_id:
+            if props.active_task_id == item.ifc_definition_id:
                 row.operator("bim.edit_task", text="", icon="CHECKMARK")
                 row.operator("bim.disable_editing_task", text="", icon="CANCEL")
-            if context.scene.BIMWorkScheduleProperties.active_task_id:
+            elif props.active_task_id:
+                if props.active_task_id in Data.tasks[item.ifc_definition_id]["IsPredecessorTo"]:
+                    row.operator("bim.unassign_predecessor", text="", icon="BACK", emboss=False).task = item.ifc_definition_id
+                else:
+                    row.operator("bim.assign_predecessor", text="", icon="TRACKING_BACKWARDS", emboss=False).task = item.ifc_definition_id
+
+                if props.active_task_id in Data.tasks[item.ifc_definition_id]["IsSuccessorFrom"]:
+                    row.operator("bim.unassign_successor", text="", icon="FORWARD", emboss=False).task = item.ifc_definition_id
+                else:
+                    row.operator("bim.assign_successor", text="", icon="TRACKING_FORWARDS", emboss=False).task = item.ifc_definition_id
+
                 row.operator("bim.add_task", text="", icon="ADD").task = item.ifc_definition_id
                 row.operator("bim.remove_task", text="", icon="X").task = item.ifc_definition_id
             else: