Example for Process Something in one thread. (for example about SQLite)

ExecSQLInSingleThread.java

package com.example.sqlite;

import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.os.Handler;
import android.os.HandlerThread;
import android.os.Looper;

import com.example.sqlite.RbSQLiteHelper;

/**
 * Created by k_morishita on 15/09/11.
 */
public class SQLiteManager {
    private final Handler mHandler;
    private final Handler mMainThreadHandler;

    public SQLiteManager() {
        HandlerThread handlerThread = new HandlerThread("SQLiteManager");
        handlerThread.start();
        mHandler = new Handler(handlerThread.getLooper());
        mMainThreadHandler = new Handler(Looper.getMainLooper());
    }


    public <T> void query(final SqlQuery<T> executor) {
        query(executor, mMainThreadHandler);
    }

    public <T> void query(final SqlQuery<T> executor, final Handler callbackHandler) {
        mHandler.post(new Runnable() {
            @Override
            public void run() {
                // TODO: Readable を取るほうが自然だろう・・・
                SQLiteDatabase database = RbSQLiteHelper.getWritable(null);  // Readable!!
                try {
                    final T ret = executor.exec(database);
                    callbackHandler.post(new Runnable() {
                        @Override
                        public void run() {
                            executor.onSuccess(ret);
                        }
                    });
                } catch (final Exception e) {
                    callbackHandler.post(new Runnable() {
                        @Override
                        public void run() {
                            executor.onError(e);
                        }
                    });
                }
            }
        });
    }

    public void exec(final SqlExec executor) {
        exec(executor, mMainThreadHandler);
    }

    public void exec(final SqlExec executor, final Handler callbackHandler) {
        mHandler.post(new Runnable() {
            @Override
            public void run() {
                try {
                    SQLiteDatabase database = RbSQLiteHelper.getWritable(null);
                    try {
                        database.beginTransaction();
                        executor.exec(database);
                        database.setTransactionSuccessful();
                    } finally {
                        database.endTransaction();
                    }
                    callbackHandler.post(new Runnable() {
                        @Override
                        public void run() {
                            executor.onSuccess();
                        }
                    });
                } catch (final Exception e) {
                    callbackHandler.post(new Runnable() {
                        @Override
                        public void run() {
                            executor.onError(e);
                        }
                    });
                }
            }
        });
    }

    public interface SqlQuery<T> {
        T exec(SQLiteDatabase database);
        void onSuccess(T result);
        void onError(Exception e);
    }

    public interface SqlExec {
        void exec(SQLiteDatabase database);
        void onSuccess();
        void onError(Exception e);
    }
}

class AnyEntity {}

class Usage {
    private SQLiteManager mSqlManager;

    public void whenRead() {
        mSqlManager.query(new SQLiteManager.SqlQuery<AnyEntity>() {
            @Override
            public AnyEntity exec(SQLiteDatabase database) {
                Cursor cursor = database.rawQuery("...", null);
                AnyEntity ret = null;  // fetch data from cursor
                return ret;
            }

            @Override
            public void onSuccess(AnyEntity result) {
                // do something
            }

            @Override
            public void onError(Exception e) {
                // handle exception
            }
        });
    }

    public void whenWrite() {
        mSqlManager.exec(new SQLiteManager.SqlExec() {
            @Override
            public void exec(SQLiteDatabase database) {
                // do something with database
            }

            @Override
            public void onSuccess() {
                // do something
            }

            @Override
            public void onError(Exception e) {
                // handle exception
            }
        });
    }
}