qt - use of qpropretyanimation desirably -

in program have built qpropertyanimation , add item , pos() property. override keypressevent. , using of keys consist of j, f, z item go forward ,go back , jump.

according gravity when item jump should fall. purpose call down function. item once jump don't fall. have problem: when first press j , f (forward , back) item animate desirably next times item go forward , go of scene.

i mean should animated example 40 pixel animated 800 pixel.

class mainwindow : public qmainwindow {     q_object  public:     explicit mainwindow(qwidget *parent = 0);     qpoint start;     qpoint end;     ~mainwindow(); private:     qgraphicsview* view;     qgraphicsscene* scene;     void keypressevent(qkeyevent* k);     myqgraphicsobject* m;     qpropertyanimation* pr;     qelapsedtimer* timer;     int f;     int u;     int b;     void forward();     void up();     void back();     void down(); };  mainwindow::mainwindow(qwidget *parent) :         qmainwindow(parent) {     view=new qgraphicsview;     scene=new qgraphicsscene;     m=new myqgraphicsobject;     pr=new qpropertyanimation(m,"pos");     view->setscene(scene);     view->resize(800,800);     view->setfixedsize(800,800);     setcentralwidget(view);     scene->additem(m);     start= qpoint(0,0);     f=30;     u=-30;     b=-30; }  void mainwindow::keypressevent(qkeyevent *k) {     switch (k->key()) {     case qt::key_j: {         forward();         break;         }    case qt::key_z: {         up();         down();         break;         }    case qt::key_f: {         back();         break;         }    default:         break;    } }  void mainwindow::forward() {     end.setx(f);     pr->setendvalue(end);     pr->setduration(1000);     pr->seteasingcurve(qeasingcurve::linear);     pr->start();     f+=40; }  void mainwindow::up() {     end.sety(u);     pr->setendvalue(end);     pr->setduration(1000);     pr->seteasingcurve(qeasingcurve::linear);     pr->start();     u-=30;     pr->pause(); }  void mainwindow::back() {     end.setx(b);     pr->setendvalue(end);     pr->setduration(1000);     pr->seteasingcurve(qeasingcurve::linear);     pr->start();     b-=40; }  void mainwindow::down() {     u+=30;     end.sety(u);     pr->setendvalue(end);     pr->setduration(1000);     pr->seteasingcurve(qeasingcurve::linear);     pr->start(); } 

you should not use resize , setfixedsize on view because use in setcentralwidget , size managed layout. should use setfixedsize on main window instead.

animations asynchonous. example, when call up(); down(), these functions executed without 1-second pause. also, starting animation when it's started has no effect.

usually animations used in such way when know need object move in next second. it's complicated receive directives user , change object's trajectory when animation performing.

here example showing correct use of animations task. object can receive 1 directive (forward, or jump) per second, , according animation performed in next second.

header:

class mainwindow : public qmainwindow {   q_object       public:   explicit mainwindow(qwidget *parent = 0);   ~mainwindow(); private:   qgraphicsview* view;   qgraphicsscene* scene;   void keypressevent(qkeyevent* k);   qgraphicsobject* object;   qpropertyanimation* animation;   qpointf pos;   double speed;    enum command {     command_none, command_jump, command_forward, command_back   };   command next_command;  private slots:   void timeout(); }; 

source:

mainwindow::mainwindow(qwidget *parent) :         qmainwindow(parent) {   view = new qgraphicsview;   scene = new qgraphicsscene;   object = scene->addwidget(new qpushbutton("test"));   object->setpos(0, -object->boundingrect().height());   animation = new qpropertyanimation(object,"pos");   animation->setduration(1000);   view->setscene(scene);   setfixedsize(800,800);   scene->addrect(-500, -200, 1000, 200);   setcentralwidget(view);   scene->additem(object);   next_command = command_none;   speed = 100;    qtimer* timer = new qtimer(this);   connect(timer, signal(timeout()), this, slot(timeout()));   timer->start(1000); }  mainwindow::~mainwindow() {}  void mainwindow::keypressevent(qkeyevent *k) {   switch (k->key()) {   case qt::key_j: {     next_command = command_forward;     break;   }   case qt::key_z: {     next_command = command_jump;     break;   }   case qt::key_f: {     next_command = command_back;     break;   }   default:     break;   } }  void mainwindow::timeout() {   //fall   if (pos.y() < 0) {     pos.sety(pos.y() + speed);     if (pos.y() >= 0) {       pos.sety(0);     }   }   //action   switch(next_command) {   case command_forward:     pos.setx(pos.x() + speed);     break;   case command_back:     pos.setx(pos.x() - speed);     break;   case command_jump:     if (pos.y() == 0) {       pos.sety(pos.y() - speed);     }     break;   default:     break;   }   next_command = command_none;   animation->stop();   animation->setendvalue(pos - qpointf(0, object->boundingrect().height()));   animation->start(); }