android - button object returning null -

<com.bakar.core.materialdesign.views.buttonfloat         android:id="@+id/buttton_float"         android:layout_width="wrap_content"         android:layout_height="wrap_content"         android:layout_alignparentbottom="true"         android:layout_alignparentright="true"         android:layout_marginright="24dp"         android:background="@color/app_primary_color"         materialdesign:animate="true"         materialdesign:icondrawable="@drawable/ic_action_new" /> 

this declaration of button in layout

this custom class of button.

package com.bakar.core.materialdesign.views;  import android.animation.objectanimator; import android.annotation.targetapi; import android.content.context; import android.graphics.bitmap; import android.graphics.bitmap.config; import android.graphics.canvas; import android.graphics.paint; import android.graphics.porterduff.mode; import android.graphics.porterduffxfermode; import android.graphics.rect; import android.graphics.drawable.drawable; import android.os.build; import android.util.attributeset; import android.view.animation.bounceinterpolator; import android.widget.imageview; import android.widget.imageview.scaletype; import android.widget.relativelayout; import android.widget.textview;  import com.bakar.r; import com.bakar.utils.utils; import com.nineoldandroids.view.viewhelper;   public class buttonfloat extends button {      int sizeicon = 24;     int sizeradius = 28;       imageview icon; // icon of float button     drawable drawableicon;      public boolean isshow = false;      float showposition;     float hideposition;       public buttonfloat(context context, attributeset attrs) {         super(context, attrs);         setbackgroundresource(r.drawable.background_button_float);         sizeradius = 28;         setdefaultproperties();         icon = new imageview(context);         icon.setadjustviewbounds(true);         icon.setscaletype(scaletype.center_crop);         if (drawableicon != null) {             icon.setimagedrawable(drawableicon);         }         relativelayout.layoutparams params = new relativelayout.layoutparams(utils.dptopx(sizeicon, getresources()), utils.dptopx(sizeicon, getresources()));         params.addrule(relativelayout.center_in_parent, relativelayout.true);         icon.setlayoutparams(params);         addview(icon);      }      protected void setdefaultproperties() {         ripplespeed = utils.dptopx(2, getresources());         ripplesize = utils.dptopx(5, getresources());         setminimumwidth(utils.dptopx(sizeradius * 2, getresources()));         setminimumheight(utils.dptopx(sizeradius * 2, getresources()));         super.background = r.drawable.background_button_float; //      super.setdefaultproperties();     }       // set atributtes of xml view     protected void setattributes(attributeset attrs) {         //set background color         // color resource         int bacgroundcolor = attrs.getattributeresourcevalue(androidxml, "background", -1);         if (bacgroundcolor != -1) {             setbackgroundcolor(getresources().getcolor(bacgroundcolor));         } else {             // color hexadecimal             background = attrs.getattributeintvalue(androidxml, "background", -1);             if (background != -1)                 setbackgroundcolor(background);         }          // set ripple color         // color resource         int ripplecolor = attrs.getattributeresourcevalue(materialdesignxml,                 "ripplecolor", -1);         if (ripplecolor != -1) {             setripplecolor(getresources().getcolor(ripplecolor));         } else {             // color hexadecimal             int background = attrs.getattributeintvalue(materialdesignxml, "ripplecolor", -1);             if (background != -1)                 setripplecolor(background);             else                 setripplecolor(makepresscolor());         }         // icon of button         int iconresource = attrs.getattributeresourcevalue(materialdesignxml, "icondrawable", -1);         if (iconresource != -1)             drawableicon = getresources().getdrawable(iconresource);         final boolean animate = attrs.getattributebooleanvalue(materialdesignxml, "animate", false);         post(new runnable() {              @override             public void run() {                 showposition = viewhelper.gety(buttonfloat.this) - utils.dptopx(24, getresources());                 hideposition = viewhelper.gety(buttonfloat.this) + getheight() * 3;                 if (animate) {                     viewhelper.sety(buttonfloat.this, hideposition);                     show();                 }             }         });      }      integer height;     integer width;      @override     protected void ondraw(canvas canvas) {         super.ondraw(canvas);         if (x != -1) {             rect src = new rect(0, 0, getwidth(), getheight());             rect dst = new rect(utils.dptopx(1, getresources()), utils.dptopx(2, getresources()), getwidth() - utils.dptopx(1, getresources()), getheight() - utils.dptopx(2, getresources()));             canvas.drawbitmap(cropcircle(makecircle()), src, dst, null);             invalidate();         }     }       public imageview geticon() {         return icon;     }      public void seticon(imageview icon) {         this.icon = icon;     }      public drawable getdrawableicon() {         return drawableicon;     }      @targetapi(build.version_codes.jelly_bean)     public void setdrawableicon(drawable drawableicon) {         this.drawableicon = drawableicon;         try {             icon.setbackground(drawableicon);         } catch (nosuchmethoderror e) {             icon.setbackgrounddrawable(drawableicon);         }     }      public bitmap cropcircle(bitmap bitmap) {         bitmap output = bitmap.createbitmap(bitmap.getwidth(),                 bitmap.getheight(), config.argb_8888);         canvas canvas = new canvas(output);          final int color = 0xff424242;         final paint paint = new paint();         final rect rect = new rect(0, 0, bitmap.getwidth(), bitmap.getheight());          paint.setantialias(true);         canvas.drawargb(0, 0, 0, 0);         paint.setcolor(color);         canvas.drawcircle(bitmap.getwidth() / 2, bitmap.getheight() / 2,                 bitmap.getwidth() / 2, paint);         paint.setxfermode(new porterduffxfermode(mode.src_in));         canvas.drawbitmap(bitmap, rect, rect, paint);         return output;     }      @override     public textview gettextview() {         return null;     }      public void setripplecolor(int ripplecolor) {         this.ripplecolor = ripplecolor;     }      public void show() {         objectanimator animator = objectanimator.offloat(buttonfloat.this, "y", showposition);         animator.setinterpolator(new bounceinterpolator());         animator.setduration(1500);         animator.start();         isshow = true;     }      public void hide() {          objectanimator animator = objectanimator.offloat(buttonfloat.this, "y", hideposition);         animator.setinterpolator(new bounceinterpolator());         animator.setduration(1500);         animator.start();          isshow = false;     }      public boolean isshow() {         return isshow;     } } 

this how using button in fragment class

private buttonfloat mbutton;  mbutton=(buttonfloat)getactivity().findviewbyid(r.id.button_float); mbutton.setonclicklistener(new view.onclicklistener() {         @override         public void onclick(view v) {             log.e("button","click");         }     }); 

this giving me null pointer exception.

ids different. in xml use @+id/buttton_float in java code use findviewbyid(r.id.button_float).