Category Archives: QT

My Android QT app crashes at qt_qFindChild_helper.

I have an Android QT app with more than has 14K active users at the moment of writing this post. The app is relatively stable, its crash rate is 0.34%:


Adding interstitial ads to a QT application on Android platform

I keep working on my Lines Game and probably I try to make it the best Lines Game in the world, but there is some disappointing incident that prevents it from being the best and makes it a usual game that glitches a bit. To see the glitch in action download the beta version of the game.

Adding Interstitial Ads to a QT application on Android platform is an interesting and relatively exciting job. I learned the following facts while doing it:

  1. To build my app with Google Play Services I add dependency to build.gradle and add and to the manifest.
  2. I do not specify additional permissions (uses-permission attributes INTERNET, WRITE_EXTERNAL_STORAGE, ACCESS_NETWORK_STATE) required by ads, but they are detected automatically when I upload the app to Google Play store and the used is not prompted to allow them when the app starts.
  3. QT main thread (on which QML UI is run) is not Android UI thread. So I cannot call Java advertising API from QML or C++ directly, but all the calls should be queued with runOnUiThread method.
  4. To access Context required by Java advertising API I replace QtActivity with my own custom activity that implements all the advertising logic and forwards all the lifecycle events to original QtActivity.
  5. When the interstitial ad is open my activity is paused and stopped (onPaused / onStopped event handlers are called in Java and onApplicationStateChanged with Qt::ApplicationInactive / Qt::ApplicationSuspended respectively ) and when the interstitial ad is closed my activity is resumed but in different ways either with onRestart.

Compiling OpenSSL 1.1 with MSVC2017 for using with QT 5.13

QT does not work with OpenSSL 1.0 anymore. Versions QT 5.12.4 and above require OpenSSL 1.1, but fortunately OpenSSL 1.1 can be easily compiled with MS2017 as follows:

set PATH=%PATH%;C:\Perl64\bin
set PATH=%PATH%;C:\PFiles\nasm-2.14.02-win64
perl Configure VC-WIN64A

The key to the success is using ‘VS2017 x64 Native Tools Command Prompt‘, but not ‘VS2017 Developer Command Prompt’.

To make QT use OpenSSL, two dlls


should be copied to QT binary directory, for example, C:\Qt\Qt5.13.0\5.13.0\msvc2017_64\bin

How I built QT 5.11.1 for Android on Windows

I tried to build QT 5.11.1 for Android on Windows, and “configure.bat” completed successfully, but “mingw32-make” failed with with the following error:

No rule to make target 'vulkan/qvulkanfunctions_p.h', needed by '.obj\qvulkaninstance.obj'.

It is the bug fixed in QT 5.11.2 that is planned on August/September 2018.

When I build the master branch and copied the following files from it to \qtbase\src\gui\vulkan manually:


and started “mingw32-make” again I got another error:


Setting up QT Creator 4.6.1 for Android development on Windows 10

First I installed Android Studio. When it started I set an option to create the application with Native C++ support and Android NDK was automatically installed to C:\Users\AppData\Local\Android\Sdk\ndk-bundle, also I added Android-19 API level and somehow CMake was installed to C:\Users\AppData\Local\Android\Sdk\cmake\3.6.4111459. Then in QT Creator I opened Tools->Options->Devices->Android and specified the following paths:


Building QT 5.10.1 from sources with VS2017

I am not sure it is a correct way, but I was able to do this:

git clone --recursive --branch v5.10.1

and all the submodules were checked out with commit hashes tag v5.10.1 points to:

You are in 'detached HEAD' state. You can look around, make experimental
changes and commit them, and you can discard any commits you make in this
state without impacting any branches by performing another checkout.
Submodule path 'qt3d': checked out '31f424bb81cd2583920d3d521e1e01f01c2d28e2'


Installing Google Play Services on a Windows 10 with MS VS2015

If Android support is enabled in MS VS2015, it installs Android SDK without Google Play Services and I did not find an option in SDK Manager that installs them. When I started “C:\Program Files (x86)\Android\android-sdk\SDK Manager.exe” with admin privileges, it automatically offered to install some 9 packages:


Multiple views with OsgQtQuick

I wrote a sample application using OsgQtQuick that shows the Earth in two views:

with the following QML, that I copied from OsgQtQuick samples:


Qt Quick Controls 2 does not support TableView

The information provided below is outdated. QT 5.13 supports SplitView and TableView but without TableHeader yet. Probably TableHeader can be implemented with the overlays.

Qt Quick Controls 2 does not support TableView and looks like they are not going to support it, some notable missing features from Qt Quick Controls 1 also are Action, SplitView and TreeView, so the following QML code would not work:

TableView {

    TableViewColumn {
        role: "time"
        title: qsTr("date/time:")
        width: parent.width - 30

    TableViewColumn {
        role: "score"
        title: qsTr("result:")
        width: 30

    model: boardModel.list

    ScrollIndicator.vertical: ScrollIndicator { }

But there is a solution with ListView, so there can be something like this:


What packages QAudioDecoder may require on Ubuntu and CentOS?

If QAudioDecoder does not decode mp3, reporting a format error (GStreamer; Unable to start decoding process), the following package can help:
On Ubuntu:

apt-get install gstreamer0.10-fluendo-mp3

On CentOS:

yum -y install
yum install gstreamer{,1}-plugins-ugly