Dev Days, 2014 - Qt Developer Days · PDF filep.21 Copy missing Android ﬁles copy all ﬁles from /src/android/java/ to /android/ folder ... If you want to learn more

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ExtendingyourQtAndroidapplicationusingJNI

DevDays,2014

PresentedbyBogDanVatra

MaterialbasedonQt5.3,createdonNovember13,2014

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ExtendingyourapplicationusingJNI



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JNICrashCourse

JNICrashCourse

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WhatisJNIandwhydoyouneedit?

JNIistheJavaNativeInterfaceJavaNativeInterface.Itisneededtodocallsto/fromJavaworldfrom/tonative(C/C++)world.

ItisimpossibleforQttoimplementallAndroidfeatures,sotousethemyou'llneedJNItoaccessthem.

JNICrashCourse

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MissingQtAPIs

listeningforAndroidO.S.notifications:

sdcardnotifications:badremoval,eject,mounted,unmounted,etc.

networknotifications:networkup/down.

batterylevelandchargingstate.

etc.

accessingAndroidO.S.features:

telephony(Initiatecalls,MMS,SMS,etc.)

contacts

speech(TTSandSpeechRecognizer)

systemaccounts

systempreferences

NFC

USB

printing(WARNING:needsAPI-19+)

createownAndroidActivitiesandServices

JNICrashCourse

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JNICrashCourse

Usecase1:callaJavafunctionfromC/C++


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CreatetheJavafunction

1 //javafileandroid/src/com/kdab/training/MyJavaClass.java2 packagecom.kdab.training;34 publicclassMyJavaClass5 {6 //thismethodwillbecalledfromC/C++7 publicstaticintfibonacci(intn)8 {9 if(n<2)10 returnn;11 returnfibonacci(n-1)+fibonacci(n-2);12 }13 }

Demoandroid/JNIIntroDemoandroid/JNIIntro


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CallaJavamethodfromC/C++,theQtway

Let'sseewhatfibonaccifibonaccifunctioncalllookslikeusingtheQtandroidextrasmodule.

1 #Changestoyour.profile2 #....3 QT+=androidextras4 #....

1 //C++code2 #include<QAndroidJniObject>3 intfibonacci(intn)4 {5 returnQAndroidJniObject::callStaticMethod<jint>6 ("com/kdab/training/MyJavaClass"//javaclassname7 ,"fibonacci"//methodname8 ,"(I)I"//signature9 ,n);10 }

Yes,that'sallfolks!


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JNICrashCourse

Usecase2:callbackaC/C++functionfromJava


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Yourjob

declareanativemethodinJavausingnativekeyword(seeslide11)

registernativemethodinC/C++(seeslide12,slide15)

dotheactualcall(seeslide11)


gotoPage://11

gotoPage://12

gotoPage://15

gotoPage://11

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DeclareandinvoketheJavanativemethods

1 //javafileandroid/src/com/kdab/training/MyJavaClass.java2 packagecom.kdab.training;34 classMyJavaNatives5 {6 //declarethenativemethod7 publicstaticnativevoidsendFibonaciResult(intn);8 }910 publicclassMyJavaClass11 {12 //thismethodwillbecalledfromC/C++13 publicstaticintfibonacci(intn)14 {15 if(n<2)16 returnn;17 returnfibonacci(n-1)+fibonacci(n-2);18 }1920 publicstaticvoidcompute_fibonacci(intn)21 {22 //callbackthenativemethodwiththecomputedresult.23 MyJavaNatives.sendFibonaciResult(fibonacci(n));24 }25 }


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C/C++registernativemethods

RegisteringfunctionsusingJava_Fully_Qualified_Class_Name_MethodNameJava_Fully_Qualified_Class_Name_MethodNametemplate.

1 //C++code2 #include<jni.h>34 #ifdef__cplusplus5 extern"C"{6 #endif78 JNIEXPORTvoidJNICALL9 Java_com_kdab_training_MyJavaNatives_sendFibonaciResult(JNIEnv*/*env*/,10 jobject/*obj*/,11 jintn)12 {13 qDebug()<<"Computedfibonacciis:"<<n;14 }1516 #ifdef__cplusplus17 }18 #endif


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UsingJava_Fully_Qualified_Class_Name_MethodNameJava_Fully_Qualified_Class_Name_MethodName.

Pro:

easiertodeclareeasiertodeclare,youdon'tneedtospecifythefunctionsignature

easiertoregistereasiertoregister,youdon'tneedtoexplicitlyregisterit

Con:

thefunctionnamesarehugehuge:Java_com_kdab_training_MyJavaNatives_sendFibonaciResult

thelibrarywillexportlotsoffunctions

unsaferunsafer,thereisnowayfortheVMtocheckthefunctionsignature


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UseJNIEnv::RegisterNativesJNIEnv::RegisterNativestoregisternativefunctions.

Step4Step4callJNIEnv::RegisterNatives(java_class_ID,methods_vector,n_methods)

Step3Step3findtheIDofjavaclassthatdeclaresthesemethodsusingJniEnv::FindClass

Step2Step2createavectorwithallC/C++methodsthatyouwanttoregister

Step1Step1getJNIEnvpointerbydefiningJNIEXPORTjintJNI_OnLoad(JavaVM*vm,void*/*reserved*/)JNIEXPORTjintJNI_OnLoad(JavaVM*vm,void*/*reserved*/).Youcandefineit(onceper.sofile)(onceper.sofile)inany.cppfileyoulike


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UseJNIEnv::RegisterNatives

1 //C++code2 #include<jni.h>34 //defineournativemethod5 staticvoidsendFibonaciResult(JNIEnv*/*env*/,jobject/*obj*/,jintn)6 {7 qDebug()<<"Computedfibonacciis:"<<n;8 }910 //step211 //createavectorwithallourJNINativeMethod(s)12 staticJNINativeMethodmethods[]={13 {"sendFibonaciResult",//constchar*functionname;14 "(I)V",//constchar*functionsignature15 (void*)sendFibonaciResult//functionpointer}16 };


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1 //step12 //thismethodiscalledautomaticallybyJavaafterthe.sofileisloaded3 JNIEXPORTjintJNI_OnLoad(JavaVM*vm,void*/*reserved*/)4 {5 JNIEnv*env;6 //gettheJNIEnvpointer.7 if(vm->GetEnv(reinterpret_cast<void**>(&env),JNI_VERSION_1_6)!=JNI_OK)8 returnJNI_ERR;910 //step311 //searchforJavaclasswhichdeclaresthenativemethods12 jclassjavaClass=env->FindClass("com/kdab/training/MyJavaNatives");13 if(!javaClass)14 returnJNI_ERR;1516 //step417 //registerournativemethods18 if(env->RegisterNatives(javaClass,methods,19 sizeof(methods)/sizeof(methods[0]))<0){20 returnJNI_ERR;21 }22 returnJNI_VERSION_1_6;23 }


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Pro:

thenativefunctioncanhaveanynameyouwant

thelibraryneedstoexportonlyonefunction(JNI_OnLoad)(JNI_OnLoad).

safersafer,becausetheVMchecksthedeclaredsignature

Con:

isslightlyhardertouse


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SDCardNotificationsExample


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Gameplan

PlumbingPlumbing

understandingAndroidfiles

howtouseanexternalIDEtomanagetheJavapart

importexistingAndroidfiles

debugJava

ArchitectureArchitecture

howtoextendtheJavapartofyourQtApplication

howtodosafecallsfromQtthreadtoAndroidUIthread

howtodosafecallsfromAndroidUIthreadtoQtthread


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UnderstandingAndroidfiles


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CopymissingAndroidfiles

copyallfilesfrom<qt_install_path>/src/android/java/to<your_src>/android/folder

makesureyour.profilehasANDROID_PACKAGE_SOURCE_DIRANDROID_PACKAGE_SOURCE_DIRpropertyset

ANDROID_PACKAGE_SOURCE_DIR=$$PWD/android


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MeaningoftheAndroidfiles

AndroidManifest.xml-isthesamefilecopiedbyQtCreatorwhenyouclickonCreateCreateAndroidManifest.xmlAndroidManifest.xmlbutton.

version.xml-isusedbyQtCreatortoupdateyourexistingAndroidfiles

res/values/libs.xml-thisfilecontainstheinformationabouttheneededlibs

res/values(-*)/strings.xml-thesefilescontainthe(translated)stringsneededbyJavapart

src/org/kde/necessitas/ministro/*.aidl-thesefilesareusedtoconnecttoMinistroservice

src/org/qtproject/qt5/android/bindings/QtApplication.java-thisclasscontainsallthelogicneededtoforwardalltheactivitycallstotheactivitydelegate

src/org/qtproject/qt5/android/bindings/QtActivity.java-thisistheapplicationactivityclass,itcontainsthelogictoconnecttoMinistroortounpackthebundledQtlibs.Italsoforwardsallcallstotheactivitydelegate.


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UsinganexternalIDEforJavapart


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UsinganexternalIDEtoextendtheJavapart

Sadly,theJavasupportinQtCreatorisclosetozero,soweneedtouseanexternalIDEtoeasilyextendtheJavapart.AndroidprovidestwopowerfulIDEs:

Eclipse

AndroidStudio(thisisverygoodandstableeventhoughitislabeledasbeta).


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Eclipseusers

IfyouarenotusingADTbundle,thenmakesureyouhaveallADTpluginsinstalledinEclipse.


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UsinganexternalIDE

TheexternalIDEwillbeusedto:

importexistingAndroidfiles

createandeditJavafiles

debugJavapart

TheexternalIDEwillNOTNOTbeusedtoruntheapplication,westillneedQtCreatorforthatjob!


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Thispresentationwillteachyouonlytheverybasicusageofbothofthem.Ifyouwanttolearnmorepleasechecktheirowndocumentation.Alsoit'suptoyouwhichoneyouchoosetouse.


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ImportexistingAndroidfilesinEclipse


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WARNING

BeforeyoustarttoimporttheprojectmakesuremakesuretheBuildAutomaticallyBuildAutomaticallyfeatureisturnedOFFisturnedOFF!Otherwisewhenyoustarttobuildyourprojectyou'llgetlotsofmysteriousbuildproblems.UncheckProjectProject->BuildAutomaticallyBuildAutomatically


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ImportinginEclipse

FileFile->NewNew->Project...Project...


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ImportinginEclipse

ChooseAndroidProjectfromExistingCodeAndroidProjectfromExistingCodewizard


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ImportinginEclipse

SelecttherootfolderofyourAndroidfiles(itshouldbeyour_qt_src/androidyour_qt_src/android)andpressFinishFinishbutton.


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ImportexistingAndroidfilesinAndroidStudio


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ImportinginAndroidStudio

FileFile->Importproject...Importproject... doesallthemagic,youjustneedtoselecttherootfolderofyourAndroidfiles(itshouldbeyour_qt_src/androidyour_qt_src/android)andcontinuethewizarduntilitisfinished.


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DebuggingJavapart

DebuggingJavapart

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DebugwithEclipse

setthebreakpoints

switchtoDDMSperspective(WindowWindow->OpenperspectiveOpenperspective->DDMSDDMS)

starttheapplication(usingQtCreator)

waitforapplicationtostart

selecttheapplication

clickthedebugicon

DebuggingJavapart

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DebugwithAndroidStudio

setthebreakpoints

attachdebugger(RunRun->AttachdebuggertoAndroidprocessAttachdebuggertoAndroidprocess)

starttheapplication(usingQtCreator)

waitforapplicationtostart

selecttheapplication

clicktheOKOKbutton

DebuggingJavapart

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Debuggingtipsandtricks

Theproblemcomeswhenweneedtostartthedebuggingveryearly.Todothatwearegoingtousetheoldfashionedsleeptrick.ThisishowourcustomcustomonCreateonCreatefunctionlooks:

1 @Override2 publicvoidonCreate(BundlesavedInstanceState)3 {4 try{5 Thread.sleep(10000);6 }catch(InterruptedExceptione){7 e.printStackTrace();8 }9 ....10 }

DebuggingJavapart

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Architecturediagram


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ExtendingJavapart

ExtendingJavapart

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Extending,notchanging

Youshouldnotchangeanyoftheexisting.javafiles,insteadyoushouldextendthem

ThereisnoneedtoextendtheQtApplicationapplicationclass

YoushouldextendonlytheQtActivityclass.TheActivityobjectisveryimportant,you'llneedittoinstantiatemostoftheAndroidclasses

Demoandroid/SD_Card_NotificationsDemoandroid/SD_Card_Notifications

ExtendingJavapart

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ExtendingQtActivity

1 //src/com/kdab/training/MyActivity.java2 packagecom.kdab.training;34 importandroid.os.Bundle;5 importorg.qtproject.qt5.android.bindings.QtActivity;67 publicclassMyActivityextendsQtActivity8 {9 //we'llneeditinBroadcastReceiver10 publicstaticMyActivitys_activity=null;1112 //everytimeyouoverrideamethod,alwaysmakesureyou13 //thencallsupermethodaswell14 @Override15 publicvoidonCreate(BundlesavedInstanceState)16 {17 s_activity=this;18 super.onCreate(savedInstanceState);19 }2021 @Override22 protectedvoidonDestroy()23 {24 super.onDestroy();25 s_activity=null;26 }27 }

ExtendingJavapart

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ExtendingJavapart

ChangedefaultactivitytoAndroidManifest.xml,from:

1 <activity...2 android:name="org.qtproject.qt5.android.bindings.QtActivity"3 ...>;

To:

1 <activity...2 android:name="com.kdab.training.MyActivity"3 ...>;

ExtendingJavapart

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NativeFunctions.javapart1

1 publicclassNativeFunctions{2 //declarethenativefunctions3 //thesefunctionswillbecalledbytheBroadcastReceiverobject4 //whenitreceivesanewnotification5 publicstaticnativevoidonReceiveNativeMounted();6 publicstaticnativevoidonReceiveNativeUnmounted();78 //thisstaticmethodiscalledbyC/C++toregistertheBroadcastReceiver.(step1)9 publicstaticvoidregisterBroadcastReceiver(){10 if(MyActivity.s_activity!=null){11 //QtisrunningonadifferentthreadthanAndroid.(step2)12 //InordertoregisterthereceiverweneedtoexecuteitintheUIthread13 MyActivity.s_activity.runOnUiThread(newRegisterReceiverRunnable());14 }15 }16 }

ExtendingJavapart

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1 classRegisterReceiverRunnableimplementsRunnable2 {3 //Step34 //thismethodiscalledonAndroidUiThread5 @Override6 publicvoidrun(){7 IntentFilterfilter=newIntentFilter();8 filter.addAction(Intent.ACTION_MEDIA_MOUNTED);9 filter.addAction(Intent.ACTION_MEDIA_UNMOUNTED);10 filter.addDataScheme("file");11 //thismethodmustbecalledonAndroidUiThread12 MyActivity.s_activity.registerReceiver(newSDCardReceiver(),filter);13 }14 }

ExtendingJavapart

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1 classSDCardReceiverextendsBroadcastReceiver{2 @Override3 publicvoidonReceive(Contextcontext,Intentintent){4 //Step45 //callthenativemethodwhenitreceivesanewnotification6 if(intent.getAction().equals(Intent.ACTION_MEDIA_MOUNTED))7 NativeFunctions.onReceiveNativeMounted();8 elseif(intent.getAction().equals(Intent.ACTION_MEDIA_UNMOUNTED))9 NativeFunctions.onReceiveNativeUnmounted();10 }11 }

ExtendingJavapart

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Architecturediagram,Javapart

ExtendingJavapart

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ExtendingC/C++part

ExtendingC/C++part

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main.cpp

1 #include"mainwindow.h"2 #include<QApplication>3 #include<QAndroidJniObject>45 intmain(intargc,char*argv[])6 {7 QApplicationa(argc,argv);89 //Step1.10 //callregisterBroadcastReceivertoregisterthebroadcastreceiver11 QAndroidJniObject::callStaticMethod<void>("com/kdab/training/NativeFunctions"12 ,"registerBroadcastReceiver"13 ,"()V");1415 MainWindow::instance().show();16 returna.exec();17 }

ExtendingC/C++part

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mainwindow.h

1 classMainWindow:publicQMainWindow2 {3 Q_OBJECT45 public:6 staticMainWindow&instance(QWidget*parent=0);78 publicslots:9 voidonReceiveMounted();10 voidonReceiveUnmounted();1112 private:13 explicitMainWindow(QWidget*parent=0);14 ~MainWindow();1516 private:17 Ui::MainWindow*ui;18 };

ExtendingC/C++part

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mainwindow.cpp

1 MainWindow&MainWindow::instance(QWidget*parent)2 {3 staticMainWindowmainWindow(parent);4 returnmainWindow;5 }67 //Step68 //CallbackinQtthread9 voidMainWindow::onReceiveMounted()10 {11 ui->plainTextEdit->appendPlainText(QLatin1String("MEDIA_MOUNTED"));12 }1314 voidMainWindow::onReceiveUnmounted()15 {16 ui->plainTextEdit->appendPlainText(QLatin1String("MEDIA_UNMOUNTED"));17 }

ExtendingC/C++part

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native.cpppart1

1 //Step4.callbackfromjavainAndroidthread2 //defineournativemethods3 staticvoidonReceiveNativeMounted(JNIEnv*/*env*/,jobject/*obj*/)4 {5 //Step5.DelegatethecalltoQtthread.6 QMetaObject::invokeMethod(&MainWindow::instance(),"onReceiveMounted"7 ,Qt::BlockingQueuedConnection);8 }910 staticvoidonReceiveNativeUnmounted(JNIEnv*/*env*/,jobject/*obj*/)11 {12 //Step5.DelegatethecalltoQtthread.13 QMetaObject::invokeMethod(&MainWindow::instance(),"onReceiveUnmounted"14 ,Qt::BlockingQueuedConnection);15 }

ExtendingC/C++part

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native.cpppart2

1 //createavectorwithallourJNINativeMethod(s)2 staticJNINativeMethodmethods[]={3 {"onReceiveNativeMounted","()V",(void*)onReceiveNativeMounted},4 {"onReceiveNativeUnmounted","()V",(void*)onReceiveNativeUnmounted},5 };67 //thismethodiscalledautomaticallybyJavaafterthe.sofileisloaded8 JNIEXPORTjintJNI_OnLoad(JavaVM*vm,void*/*reserved*/)9 {10 JNIEnv*env;//gettheJNIEnvpointer.11 if(vm->GetEnv(reinterpret_cast<void**>(&env),JNI_VERSION_1_6)!=JNI_OK)12 returnJNI_ERR;1314 //searchforJavaclasswhichdeclaresthenativemethods15 jclassjavaClass=env->FindClass("com/kdab/training/NativeFunctions");16 if(!javaClass)17 returnJNI_ERR;1819 //registerournativemethods20 if(env->RegisterNatives(javaClass,methods,21 sizeof(methods)/sizeof(methods[0]))<0){22 returnJNI_ERR;23 }24 returnJNI_VERSION_1_6;25 }

ExtendingC/C++part

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Architecturediagram,QtJNIpart

ExtendingC/C++part

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Architecturediagram,summary

ExtendingC/C++part

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Questions?

Thankyouforyourtime!

Contactus:

http://www.kdab.comhttp://www.kdab.com

[email protected]@kdab.com




http://www.kdab.com

Dev Days, 2014 - Qt Developer Days · PDF filep.21 Copy missing Android ﬁles copy all ﬁles from /src/android/java/ to /android/ folder ... If you want to learn more

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