java - Touch doesn't work in Canvas and Layout -


i start study java on android. in programs tried change color in layout background , canvas color when touch screen. thought it's easy, ...nothing happen when touch screen using implement ontouchlistener+ ontouch() .actually, log.w not shown in logcat . when use ontouchevent() in layout color changed, in canvas log.w informed me program answered touch, color didn’t change. so, have 2 issues:
1. implement ontouchlistener+ ontouch() doesn’t works @ in both cases. 2. ontouchevent() in canvas works partly , doesn’t change color.

please me understand mistakes are? wrong? tried use "return false" in ontouch() , replace listener+ontouch() in main activity class, , many others.

  **canvas**  import android.app.activity; import android.content.context; import android.graphics.canvas; import android.graphics.color; import android.os.bundle; import android.util.log; import android.view.motionevent; import android.view.view; import android.view.view.ontouchlistener; public class mainactivity extends activity  {     @override     protected void oncreate(bundle savedinstancestate) {         super.oncreate(savedinstancestate);                 setcontentview(new mycanvas(this));     } } class mycanvas extends view //implements ontouchlistener {   private int a=0;     public mycanvas(context context){         super(context);     }     @override     public   void ondraw( canvas canvas){         if(a==0)         {canvas.drawcolor(color.magenta);             }         else         { canvas.drawcolor(color.blue);             }     }    /* @override     public boolean ontouch(view view,motionevent event){         if(event.getaction()==motionevent.action_down) {             log.w("my", "inside ontouch");             if(a==0)a=1;             else a=0;             invalidate();         }         return false;     }*/    public boolean ontouchevent(motionevent event){         if(event.getaction()==motionevent.action_down) {             log.w("my", "inside ontouch");             if(a==0)a=1;             else a=0;             invalidate();         }         return true;     } }   **layout**  <?xml version="1.0" encoding="utf-8"?> <android.support.constraint.constraintlayout xmlns:android="http://schemas.android.com/apk/res/android"     xmlns:app="http://schemas.android.com/apk/res-auto"     xmlns:tools="http://schemas.android.com/tools"     android:id="@+id/rayout1"     android:layout_width="match_parent"     android:layout_height="match_parent"     android:background="@color/coloraccent"     tools:context="com.example.cathy.touchlayout.mainactivity">     <textview         android:layout_width="wrap_content"         android:layout_height="wrap_content"         android:text="hello world!"         app:layout_constraintbottom_tobottomof="parent"         app:layout_constraintleft_toleftof="parent"         app:layout_constraintright_torightof="parent"         app:layout_constrainttop_totopof="parent" /> </android.support.constraint.constraintlayout>    import android.graphics.color; import android.support.constraint.constraintlayout; import android.support.v7.app.appcompatactivity; import android.os.bundle; import android.view.motionevent; import android.view.view; public class mainactivity extends appcompatactivity //implements view.ontouchlistener {     constraintlayout mylayout;     @override     protected void oncreate(bundle savedinstancestate) {         super.oncreate(savedinstancestate);         setcontentview(r.layout.activity_main);         mylayout=(constraintlayout)findviewbyid(r.id.rayout1);     }       public boolean ontouchevent( motionevent event) {         if(event.getaction()==motionevent.action_down) {             mylayout.setbackgroundcolor(color.blue);         }         return true;     }    /*  @override        public boolean ontouch( view v,motionevent event) {         if(event.getaction()==motionevent.action_down) {             mylayout.setbackgroundcolor(color.blue);         }         return true;     }*/ }


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