java - Is it appropriate to use the Decorator Pattern while extending RecyclerView.Adapter? -

i've written footeradapter seems work perfectly.

i realised viewholder has field mposition among others hold state in each element leading me suspect header not achievable usage of decorator pattern, because hold different position in each adapter.

that is, except if wrapper/decorator adapter didn't alter other elements. say: footers ok, long data not need binded them.

if wrapper adapters possible need more access viewholder? i'm not sure how fields

intended usage:

headerview = new view( context ); footerview = new view( context );  myadapter myadapter = new myadapter(); headeradapter headeradapter = new headeradapter( myadapter , headerview ); footeradapter footeradapter = new footeradapter( headeradapter , footerview );  recyclerview recyclerview = new recyclerview(); recyclerview.setadapter( footeradapter ); 

this cool, because add headers & footers arbitrary adapter , not have worry indexing , offsetting item counts.

footeradapter.java

public class footeradapter extends recyclerview.adapter {     private static final string tag = "footeradapter";     private final recyclerview.adapter<recyclerview.viewholder> wrappedadapter;      private view footer;      public static final int footer_type = 0x72846fe;      public footeradapter( recyclerview.adapter<recyclerview.viewholder> wrappedadapter , view footer )     {         this.footer = footer;         this.wrappedadapter = wrappedadapter;         wrappedadapter.registeradapterdataobserver(new thisobserver());     }      @override     public int getitemviewtype(int position)     {         if( position == wrappedadapter.getitemcount() ) return footer_type;         return wrappedadapter.getitemviewtype(position);     }      @override     public recyclerview.viewholder oncreateviewholder(viewgroup parent, int viewtype) {         if( viewtype == footer_type )         {             return new recyclerview.viewholder( footer ){};         }else         {             return wrappedadapter.oncreateviewholder(parent,viewtype);         }     }      @override     public void onbindviewholder(recyclerview.viewholder holder, int position) {         if( holder.getitemviewtype() == footer_type ) return;         return wrappedadapter.bindviewholder( holder , position );     }      @override     public int getitemcount() {         return wrappedadapter.getitemcount() + 1;     }       private class thisobserver extends adapterdataobserver     {         public void onchanged() {             notifydatasetchanged();         }          public void onitemrangechanged(int positionstart, int itemcount) {             notifyitemrangechanged(positionstart,itemcount);         }          public void onitemrangeinserted(int positionstart, int itemcount) {             notifyitemrangeinserted(positionstart,itemcount);         }          public void onitemrangeremoved(int positionstart, int itemcount) {             notifyitemrangeremoved(positionstart,itemcount);         }          public void onitemrangemoved(int fromposition, int toposition, int itemcount) {             int lower = math.min( fromposition , toposition );             int upper = math.max( fromposition , toposition );             for( int = itemcount-1 ; < itemcount ; i++ )             {                 notifyitemmoved(upper+i,lower+i+(toposition-fromposition));             }         }     } } 

headeradapter.java

public class headeradapter extends recyclerview.adapter {     private static final string tag = "headeradapter";     private final recyclerview.adapter<recyclerview.viewholder> wrappedadapter;      private view header;      public static final int header_type = 0x747efe;      public headeradapter( recyclerview.adapter<recyclerview.viewholder> wrappedadapter , view header )     {         this.header = header;         this.wrappedadapter = wrappedadapter;         wrappedadapter.registeradapterdataobserver(new thisobserver());     }      @override     public int getitemviewtype(int position)     {         return position == 0 ? header_type : wrappedadapter.getitemviewtype(position - 1);     }      @override     public recyclerview.viewholder oncreateviewholder(viewgroup parent, int viewtype) {         if( viewtype == header_type )         {             return new recyclerview.viewholder( header ){};         }else         {             return new recyclerview.viewholder( wrappedadapter.oncreateviewholder(parent,viewtype).itemview ){};             // thought kind of wrapping (hack?) might              // around different indexing in different adapters,              // doesn't work, needs more              // information, or able observe changes in              // "child" viewholder.         }     }      @override     public void onbindviewholder(recyclerview.viewholder holder, int position) {         if( holder.getitemviewtype() != header_type ) wrappedadapter.bindviewholder( holder , position - 1 );     }      @override     public int getitemcount() {         return wrappedadapter.getitemcount() + 1;     }       private class thisobserver extends recyclerview.adapterdataobserver     {          public void onchanged() {             notifydatasetchanged();         }          public void onitemrangechanged(int positionstart, int itemcount) {             notifyitemrangechanged(1+positionstart,itemcount);         }          public void onitemrangeinserted(final int positionstart, final int itemcount) {             notifyitemrangeinserted(1 + positionstart, itemcount);         }          public void onitemrangeremoved(int positionstart, int itemcount) {             notifyitemrangeremoved(1 + positionstart, itemcount);         }          public void onitemrangemoved(int fromposition, int toposition, int itemcount) {             fromposition++;             toposition++;             int lower = math.min( fromposition , toposition );             int upper = math.max( fromposition , toposition );             for( int = itemcount-1 ; < itemcount ; i++ ) notifyitemmoved(upper+i,lower+i+(toposition-fromposition));         }     } } 

so turns out footer wasn't perfect.

so can't use pattern headers or footers.

when remove items footer wants stick around @ highest index reached.

there many package level variables don't have access to. think intended usage write entire class in 1 go.

headers , footers better fit layoutmanager anyway, mean, know are, don't need "adapting"