Tag Archives: bug

[Solved] onDataChanged not called, Android Wearable

I was doing a school project on Android Wearable for the past few days. A strange bug happened.

I used  Wearable.DataApi.putDataItem(mGoogleApiClient, putDataReq)for triggering  onDataChanged in WearableListenerService. However, I noticed that sometimes  onDataChanged is not called even though the putDataItem method has fired.

The strange thing is this bug only happens on the first call, subsequently the calls trigger normally. More interestingly, the bug only happens sometimes, once in a while, the first call will trigger normally.

Aftering debugging and getting nowhere, I decided to get help from stackoverflow. I found an answer that was relevant:


The answer suggests adding a time field into the DataMap  so that the data is really changed every time. I did not think that was the cause of the problem, because I followed the online tutorial and had a count value in my DataMap, which increments every time. This should have caused the data to change every time.

However, after I added the time field into the DataMap, the bug disappeared. So it was true that my old implementation was not causing any changes. The count value did not work. After thinking through the process again, I figured out why.

The count did increase after each call, from 0 to 1, 2, 3, … However, those values are stored in the DataMap within the wearable device, not on the phone. So it was possible that wearable device already has a DataMap in which there is a data with count 0, although my phone app does not have the DataMap yet. When I send a new DataMap with count 0 from phone to the wearable, that DataMap is already present on the wearable, and hence no change will be detected and onDataChanged will not be triggered.

For time, since the current time is unique and always increasing, there would not be a case where the time in DataMap on the phone already exists on the wearable, hence always triggering onDataChanged.

[Solved]Lag issue with meteor and stuck at loading

Meteor is the web framework that I have been learning for past few weeks. It is powerful and easy to learn but some functions are still under-developed hence some bugs.

When playing with the Todo List example, I discovered a bug in the example. The example has a function to display a “loading text” in item panel when the user selects a new list and the corresponding items are being loaded from database. However, if the user switches between the lists very fast and selects the next list before the current list is loaded, the item panel will be forever stuck at loading. This may not be a issue when running on a local server but it would be much more serious if the Internet connection to server is slow.

I am not entirely sure of the cause of this problem but it has to do with how DOM elements are updated when the variables get changed. For some reason, if the Meteor.subscribe() method does not return before the next execution, the DOM elements will not be updated.

I solved this issue by using a session variable, which is altered when new list is selected. In this way, a selection of new list will always trigger the change in session variable and hence update DOM accordingly. Below is the relevant code modified by me:

This technique is related to meteor’s reactivity, here is the reference on Reactivity for meteor.