In this android programming source code example, we are going to limit the amount of rows retreived from Android Room Database.
You can copy and adopt this source code example to your android project without reinventing the wheel.
Below is a step by step source code to limit the amount of rows retreived from Android Room Database.
activity_main.xml
<?xml version="1.0" encoding="utf-8"?> <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent" android:layout_height="match_parent"> <android.support.v7.widget.RecyclerView android:id="@+id/list" android:layout_width="match_parent" android:layout_height="match_parent"/> </RelativeLayout>
MainActivity.java
import android.content.Context; import android.support.v7.app.AppCompatActivity; import android.os.Bundle; import android.support.v7.widget.DividerItemDecoration; import android.support.v7.widget.LinearLayoutManager; import android.support.v7.widget.RecyclerView; import android.view.LayoutInflater; import android.view.View; import android.view.ViewGroup; import android.widget.TextView; import android.widget.Toast; import com.bluapp.androidview.R; import java.util.List; import io.reactivex.Completable; import io.reactivex.CompletableObserver; import io.reactivex.android.schedulers.AndroidSchedulers; import io.reactivex.disposables.Disposable; import io.reactivex.functions.Action; import io.reactivex.schedulers.Schedulers; public class RoomDatabaseActivity20 extends AppCompatActivity { private RecyclerView list; private adapter recyclerAdapter; private UserDatabase userDatabase; private List<User> responseList; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_room_database20); list = (RecyclerView)findViewById(R.id.list); userDatabase = UserDatabase.getInstance(this); readData(); LinearLayoutManager layoutManager = new LinearLayoutManager(this); list.setLayoutManager(layoutManager); recyclerAdapter = new adapter(RoomDatabaseActivity20.this, responseList); list.addItemDecoration(new DividerItemDecoration(RoomDatabaseActivity20.this, DividerItemDecoration.VERTICAL)); list.setAdapter(recyclerAdapter); } private void readData(){ Completable.fromAction(new Action() { @Override public void run() throws Exception { userDatabase.userDAO().getlimituserList(); } }).observeOn(AndroidSchedulers.mainThread()) .subscribeOn(Schedulers.io()) .subscribe(new CompletableObserver() { @Override public void onSubscribe(Disposable d) { } @Override public void onComplete() { responseList = userDatabase.userDAO().getlimituserList(); recyclerAdapter.setList(responseList); } @Override public void onError(Throwable e) { Toast.makeText(RoomDatabaseActivity20.this, "Empty data",Toast.LENGTH_LONG).show(); } }); } private class adapter extends RecyclerView.Adapter<adapter.myViewHolder> { Context context; List<User> responseList; public adapter(Context context, List<User> data) { this.context = context; this.responseList = data; } public void setList(List<User> resList) { this.responseList = resList; notifyDataSetChanged(); } @Override public adapter.myViewHolder onCreateViewHolder(ViewGroup parent, int viewType) { View view = LayoutInflater.from(context).inflate(R.layout.room_adapter1, parent, false); return new myViewHolder(view); } @Override public void onBindViewHolder(adapter.myViewHolder holder, int position) { holder.name.setText(responseList.get(position).getName()); } @Override public int getItemCount() { if(responseList != null){ return responseList.size(); } return 0; } public class myViewHolder extends RecyclerView.ViewHolder { TextView name; public myViewHolder(View itemView) { super(itemView); name = (TextView) itemView.findViewById(R.id.Name); } } } }
room_adapter1.xml
<?xml version="1.0" encoding="utf-8"?> <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent" android:layout_height="wrap_content"> <TextView android:id="@+id/Name" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_alignParentLeft="true" android:layout_marginTop="10dp" android:lineSpacingMultiplier="0.6" android:layout_marginLeft="10dp" android:text="Emmanuel" android:textColor="#000000" android:textSize="18sp"/> </RelativeLayout>
UserDatabase.java
import android.arch.persistence.db.SupportSQLiteDatabase; import android.arch.persistence.room.Database; import android.arch.persistence.room.Room; import android.arch.persistence.room.RoomDatabase; import android.content.Context; import android.support.annotation.NonNull; import java.util.concurrent.Executors; @Database(entities = { User.class }, version = 1, exportSchema = false) public abstract class UserDatabase extends RoomDatabase { private static final String DB_NAME ="UserDb"; private static UserDatabase instance; public abstract UserDAO userDAO(); public synchronized static UserDatabase getInstance(final Context context) { if (instance == null) { instance = Room.databaseBuilder(context, UserDatabase.class, DB_NAME) .allowMainThreadQueries().build(); } return instance; } }
User.java
import android.arch.persistence.room.ColumnInfo; import android.arch.persistence.room.Entity; import android.arch.persistence.room.Ignore; import android.arch.persistence.room.PrimaryKey; @Entity(tableName = "users") public class User { @PrimaryKey(autoGenerate = true) private int id; @ColumnInfo(name = "name") private String name; public User(int id, String name){ this.id = id; this.name = name; } @Ignore public User(String name){ this.name = name; } public int getId() { return id; } public String getName() { return name; } }
UserDAO.java
import android.arch.persistence.room.Dao; import android.arch.persistence.room.Delete; import android.arch.persistence.room.Insert; import android.arch.persistence.room.Query; import android.arch.persistence.room.Update; import java.util.ArrayList; import java.util.List; @Dao public interface UserDAO { @Query("select * from users limit 1") List<User> getlimituserList(); @Insert public void insert(User user); @Update public void update(User user); @Delete public void delete(User user); }
build.gradle
implementation 'io.reactivex.rxjava2:rxjava:2.1.9' implementation 'io.reactivex.rxjava2:rxandroid:2.0.1' implementation 'android.arch.persistence.room:runtime:1.0.0' annotationProcessor 'android.arch.persistence.room:compiler:1.0.0'
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