Thêm divider và khoảng cách item RecyclerView Android

RecyclerView ItemDecoration - Divider & Spacing

ItemDecoration là cách chuẩn để thêm divider (phân cách) và spacing (khoảng cách) cho RecyclerView mà không sửa đổi item layout.

Bước 1: Tạo dự án mới

Khởi tạo project Android Studio.

Bước 2: Layout chính (res/layout/activity_main.xml)

<?xml version="1.0" encoding="utf-8"?>
<android.support.design.widget.CoordinatorLayout 
    xmlns:android="https://schemas.android.com/apk/res/android"
    xmlns:app="https://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <android.support.design.widget.AppBarLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content">
        
        <android.support.v7.widget.Toolbar
            android:id="@+id/appbarlayout_tool_bar"
            android:layout_width="match_parent"
            android:layout_height="?attr/actionBarSize"
            android:background="@color/colorPrimary"
            app:layout_scrollFlags="scroll|snap|enterAlways"
            app:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar"
            app:popupTheme="@style/ThemeOverlay.AppCompat.Light" />
            
    </android.support.design.widget.AppBarLayout>

    <android.support.v7.widget.RecyclerView
        android:id="@+id/recycler_view"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:layout_behavior="@string/appbar_scrolling_view_behavior" />

</android.support.design.widget.CoordinatorLayout>

Bước 3: Divider Drawable (res/drawable/divider.xml)

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="https://schemas.android.com/apk/res/android"
    android:shape="rectangle">
    <solid android:color="@color/colorPrimary" />
    <size android:height="1dp" /> <!-- Chiều cao divider dọc -->
</shape>

Bước 4: Adapter (src/CustomAdapter.java)

package com.example.myapplication;

import android.content.Context;
import android.support.annotation.NonNull;
import android.support.v7.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;
import java.util.ArrayList;

public class CustomAdapter extends RecyclerView.Adapter<CustomAdapter.MyViewHolder> {
    private Context context;
    private ArrayList<String> list;
    private OnClickInterface onClickInterface;
    
    public static class MyViewHolder extends RecyclerView.ViewHolder {
        public TextView title;
        
        public MyViewHolder(View view) {
            super(view);
            title = view.findViewById(R.id.title);
        }
    }
    
    public CustomAdapter(Context context, ArrayList<String> list, OnClickInterface onClickInterface) {
        this.context = context;
        this.list = list;
        this.onClickInterface = onClickInterface;
    }
    
    @NonNull
    @Override
    public MyViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        View itemView = LayoutInflater.from(parent.getContext())
            .inflate(R.layout.list_row, parent, false);
        return new MyViewHolder(itemView);
    }
    
    @Override
    public void onBindViewHolder(@NonNull MyViewHolder holder, final int position) {
        holder.title.setText(list.get(position));
        holder.itemView.setOnClickListener(v -> {
            if (onClickInterface != null) {
                onClickInterface.onItemClick(position);
            }
        });
    }
    
    @Override
    public int getItemCount() {
        return list.size();
    }
}

Bước 5: Item Layout (res/layout/list_row.xml)

<?xml version="1.0" encoding="utf-8"?>
<android.support.v7.widget.CardView 
    xmlns:android="https://schemas.android.com/apk/res/android"
    xmlns:app="https://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_marginHorizontal="16dp"
    android:layout_marginVertical="8dp"
    app:cardElevation="2dp"
    app:cardCornerRadius="8dp">

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="vertical"
        android:gravity="center"
        android:padding="16dp">

        <TextView
            android:id="@+id/title"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:gravity="center"
            android:textSize="18sp" />

    </LinearLayout>
</android.support.v7.widget.CardView>

Bước 6: Interface (src/OnClickInterface.java)

package com.example.myapplication;

public interface OnClickInterface {
    void onItemClick(int position);
}

Bước 7: MainActivity.java - Cấu hình DividerItemDecoration

package com.example.myapplication;

import android.annotation.TargetApi;
import android.os.Build;
import android.os.Bundle;
import android.support.v4.content.ContextCompat;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.DefaultItemAnimator;
import android.support.v7.widget.DividerItemDecoration;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.support.v7.widget.Toolbar;
import android.widget.Toast;
import java.util.ArrayList;

public class MainActivity extends AppCompatActivity implements OnClickInterface {
    private RecyclerView recyclerView;
    private CustomAdapter mAdapter;
    private ArrayList<String> list = new ArrayList<>();
    
    @TargetApi(Build.VERSION_CODES.LOLLIPOP)
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        
        Toolbar toolbar = findViewById(R.id.appbarlayout_tool_bar);
        toolbar.setTitle("RecyclerView Dividers & Spacing");
        setSupportActionBar(toolbar);
        
        recyclerView = findViewById(R.id.recycler_view);
        recyclerView.setLayoutManager(new LinearLayoutManager(this));
        recyclerView.setItemAnimator(new DefaultItemAnimator());
        
        mAdapter = new CustomAdapter(this, list, this);
        recyclerView.setAdapter(mAdapter);
        
        // === DIVIDER (Phân cách dòng) ===
        DividerItemDecoration divider = new DividerItemDecoration(
            recyclerView.getContext(), DividerItemDecoration.VERTICAL
        );
        // Set drawable tùy chỉnh
        divider.setDrawable(ContextCompat.getDrawable(this, R.drawable.divider));
        recyclerView.addItemDecoration(divider);
        
        // === SPACING (Khoảng cách) - dùng ItemDecoration tùy chỉnh ===
        // recyclerView.addItemDecoration(new SpacesItemDecoration(16)); // Xem class dưới
        
        // Data
        for (int i = 1; i <= 20; i++) {
            list.add("Item " + i);
        }
    }
    
    @Override
    public void onItemClick(int position) {
        Toast.makeText(this, "Item " + (position + 1), Toast.LENGTH_SHORT).show();
    }
}

ItemDecoration cho Spacing (Khoảng cách)

package com.example.myapplication;

import android.graphics.Rect;
import android.support.v7.widget.RecyclerView;
import android.view.View;

public class SpacesItemDecoration extends RecyclerView.ItemDecoration {
    private final int space;
    
    public SpacesItemDecoration(int space) {
        this.space = space;
    }
    
    @Override
    public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {
        int position = parent.getChildAdapterPosition(view);
        
        outRect.left = space;
        outRect.right = space;
        outRect.bottom = space;
        
        // Top margin chỉ cho item đầu tiên
        if (position == 0) {
            outRect.top = space;
        } else {
            outRect.top = 0;
        }
    }
}

Sử dụng SpacesItemDecoration

// Thêm spacing 16dp
recyclerView.addItemDecoration(new SpacesItemDecoration(16));

DividerItemDecoration vs Custom ItemDecoration

Ẩn divider cuối cùng

// Cách 1: Override ItemDecoration
public class NoLastDividerDecoration extends DividerItemDecoration {
    public NoLastDividerDecoration(Context context, int orientation) {
        super(context, orientation);
    }
    
    @Override
    public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {
        int position = parent.getChildAdapterPosition(view);
        if (position == state.getItemCount() - 1) {
            outRect.bottom = 0; // Không divider cho item cuối
        } else {
            super.getItemOffsets(outRect, view, parent, state);
        }
    }
}

// Cách 2: XML drawable với transparent last item (khó kiểm soát)

Best Practices

• Dùng DividerItemDecoration cho divider đơn giản
• Dùng custom ItemDecoration cho spacing phức tạp (grid, staggered)
• Không thêm margin trong item layout - dùng ItemDecoration để tách biệt concerns
• Test với nhiều kích thước màn hình, orientation