Android RecycleView如何实现Item拖拽效果
Android RecycleView如何实现Item拖拽效果
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基于公司产品的优化需求，其中一个需求涉及到RecycleView的拖拽，以及拖拽后item位置的持久化，目的是可以用户自定义界面偏好，并在用户下次进入本界面后，之前设置的偏好仍然有效。我写了一个小Demo用作演示效果。
先看效果（只看效果，不看颜值）
步骤1、建接口文件ItemTouchHelperViewHolder，该接口文件中描述的是选中和放开当前Item调用的方法。
publicinterfaceItemTouchHelperViewHolder{voidonItemSelected();//选中itemvoidonItemCleared();//放开item}
步骤2、写Item得ViewHolder的类，该类需要继承RecyclerView.ViewHolder类，同时要实现步骤中的接口。
publicclassItemViewHolderextendsRecyclerView.ViewHolderimplementsItemTouchHelperViewHolder{privateTextViewtvName;publicTextViewgetTvName(){returntvName;}publicvoidsetTvName(TextViewtvName){this.tvName=tvName;}publicItemViewHolder(@NonNullViewitemView){super(itemView);tvName=itemView.findViewById(R.id.tv_item_name);}@OverridepublicvoidonItemSelected(){tvName.setBackgroundColor(Color.GRAY);}@OverridepublicvoidonItemCleared(){tvName.setBackgroundColor(Color.YELLOW);}}
步骤3、建立接口文件ItemTouchHelperAdapter，该文件中描写的是移动RecycleView的Item时会调用的方法。
publicinterfaceItemTouchHelperAdapter{voidonItemMove(intfromPosition,inttoPosition);}
步骤4、实现一个适配器，继承RecyclerView.Adapter<ItemViewHolder>，同时实现步骤3的接口。
publicclassRecyclerGridAdapterextendsRecyclerView.Adapter<ItemViewHolder>implementsItemTouchHelperAdapter{privateArrayList<String>localDataSet;privateSharedPreferencessp;privateSharedPreferences.EditorspEditor;finalstaticStringSAVE_KEY="star_sort";finalstaticStringUSER_PREFERENCE="user_preference";privateContextcontext;publicRecyclerGridAdapter(ArrayList<String>dataSet,Contextcontext){StringdefaultStr=dataSet.toString();if(context!=null){this.context=context;sp=context.getSharedPreferences(USER_PREFERENCE,Context.MODE_PRIVATE);spEditor=sp.edit();StringsaveString=sp.getString(SAVE_KEY,defaultStr);//考虑，若要更改数据源，需要怎么实现todoString[]splitStr=saveString.replace("[","").replace("]","").replace("","").split(",");localDataSet=newArrayList();localDataSet.addAll(Arrays.asList(splitStr));}}@NonNull@OverridepublicItemViewHolderonCreateViewHolder(@NonNullViewGroupparent,intviewType){Viewview=LayoutInflater.from(parent.getContext()).inflate(R.layout.item_view_holder_layout,parent,false);returnnewItemViewHolder(view);}@OverridepublicvoidonBindViewHolder(@NonNullItemViewHolderholder,intposition){holder.getTvName().setText(localDataSet.get(position));}@OverridepublicintgetItemCount(){returnlocalDataSet.size();}@OverridepublicvoidonItemMove(intfromPosition,inttoPosition){Stringprve=localDataSet.remove(fromPosition);if((toPosition>fromPosition)&&(localDataSet.size()<=toPosition)){//将当前item移至最后一位localDataSet.add(prve);}else{localDataSet.add(toPosition,prve);}notifyItemMoved(fromPosition,toPosition);spEditor.putString(SAVE_KEY,localDataSet.toString());spEditor.apply();}}
步骤5、实现ItemTouchHelper.Callback接口，至于什么是ItemTouchHelper，网上一查很多解释，我这不做阐述了。
publicclassSimpleItemTouchHelperCallbackextendsItemTouchHelper.Callback{privateItemTouchHelperAdapteradapter;publicSimpleItemTouchHelperCallback(ItemTouchHelperAdapteradapter){this.adapter=adapter;}@OverridepublicintgetMovementFlags(@NonNullRecyclerViewrecyclerView,@NonNullRecyclerView.ViewHolderviewHolder){finalintdragFlags=ItemTouchHelper.UP|ItemTouchHelper.DOWN|ItemTouchHelper.LEFT|ItemTouchHelper.RIGHT;returnmakeFlag(ItemTouchHelper.ACTION_STATE_DRAG,dragFlags);}@OverridepublicbooleanonMove(@NonNullRecyclerViewrecyclerView,@NonNullRecyclerView.ViewHolderviewHolder,@NonNullRecyclerView.ViewHoldertarget){if(viewHolder.getItemViewType()!=target.getItemViewType()){returnfalse;}adapter.onItemMove(viewHolder.getAdapterPosition(),target.getAdapterPosition());returntrue;}@OverridepublicvoidonSwiped(@NonNullRecyclerView.ViewHolderviewHolder,intdirection){}@OverridepublicvoidonSelectedChanged(@NullableRecyclerView.ViewHolderviewHolder,intactionState){if(actionState==ItemTouchHelper.ACTION_STATE_DRAG){ItemTouchHelperViewHolderitemTouchHelperViewHolder=(ItemTouchHelperViewHolder)viewHolder;itemTouchHelperViewHolder.onItemSelected();}super.onSelectedChanged(viewHolder,actionState);}@OverridepublicvoidclearView(@NonNullRecyclerViewrecyclerView,@NonNullRecyclerView.ViewHolderviewHolder){super.clearView(recyclerView,viewHolder);ItemViewHolderitemViewHolder=(ItemViewHolder)viewHolder;itemViewHolder.onItemCleared();}}
步骤6，现在就可以调用啦，基于步骤5实现的ItemToucherHelper.Callback实例构建ItemTouchHelper实例，然后attach给RecycleView就好啦。
classMainActivity:AppCompatActivity(){overridefunonCreate(savedInstanceState:Bundle?){super.onCreate(savedInstanceState)valviewBinding=DataBindingUtil.setContentView<ActivityMainBinding>(this,R.layout.activity_main)with(viewBinding){vardata=ArrayList<String>()varindex=10while(index-->0){data.add(index.toString())}varadapter=RecyclerGridAdapter(data,this@MainActivity)recycleTest.layoutManager=GridLayoutManager(this@MainActivity,4)recycleTest.adapter=adaptervarcallback=SimpleItemTouchHelperCallback(adapter)varitemTouchHelper=ItemTouchHelper(callback)itemTouchHelper.attachToRecyclerView(recycleTest)}}}
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