话不多说，就是数据库的存储，将一些可以不用劳烦服务器存储的数据存储在本地，像购物车啊，断点续传下载啊，可能会记录一些数据信息，就会使用到。下面来看看SQLite基本的用法吧。
首先当然是创建数据库和表信息，新建DBHelper.java文件：
package com.dingfang.org.sqlitedemo.db;
import android.content.Context;
import android.database.DatabaseErrorHandler;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
public class DBHelper extends SQLiteOpenHelper {
/**
* 数据库名称
* 数据库的创建，不需要我们认为控制，提供数据库名称和版本号就行了
*/
private static final String DB_NAME = "download.db";
/**
* 数据库版本号
*/
private static final int VERSION = 1;
/**
* 创建表 thread_info
*/
private static final String SQL_CREATE = "create table thread_info(_id integer primary key autoincrement," +
"thread_id integer, url text, start integer, end integer, finished integer)";
/**
*删除表 thread_info
*/
private static final String SQL_DROP = "drop table if exists thread_info";
public DBHelper(Context context) {
super(context, DB_NAME, null, VERSION);
}
public DBHelper(Context context, String name, SQLiteDatabase.CursorFactory factory, int version) {
super(context, name, factory, version);
}
public DBHelper(Context context, String name, SQLiteDatabase.CursorFactory factory, int version, DatabaseErrorHandler errorHandler) {
super(context, name, factory, version, errorHandler);
}
/**
* 创建表操作
* @param sqLiteDatabase
*/
@Override
public void onCreate(SQLiteDatabase sqLiteDatabase) {
sqLiteDatabase.execSQL(SQL_CREATE);
}
/**
* 当前版本号和最新版本号进行比较，如果大于的话，就执行升级操作onUpgrade方法，否则就执行降级onDowngrade方法，
* 不过降级方法实现很简单，一般是不允许降级操作的，因为会抛异常
* @param sqLiteDatabase
* @param oldVersion
* @param newVersion
*/
@Override
public void onUpgrade(SQLiteDatabase sqLiteDatabase, int oldVersion, int newVersion) {
//本人认为，如果数据更新操作，不想删除表的话，是不是直接写一个添加字段的sql语句执行就行了。
sqLiteDatabase.execSQL(SQL_DROP);
sqLiteDatabase.execSQL(SQL_CREATE);
}
}
注释都很清楚了，上面创建了数据库，其名称是download.db，创建数据库的这个过程，程序员根本就不用关心就，我们的心思应该放在创建表上。上面看创建了表thread_info，下面我们来为表写一个实体类，为的是存储表数据时有个容器盛放，是吧。新建一个ThreadInfo实体类：
package com.dingfang.org.sqlitedemo.entity;
/**
* 线程信息
*/
public class ThreadInfo {
private int id;
private String url;
private int start;
private int end;
private int finished;
public ThreadInfo() {
}
/**
* @param id
* @param url 下载信息
* @param start 下载的位置
* @param end 下载目标位置
* @param finished 已经下载到订单位置
*/
public ThreadInfo(int id, String url, int start, int end, int finished) {
this.id = id;
this.url = url;
this.start = start;
this.end = end;
this.finished = finished;
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getUrl() {
return url;
}
public void setUrl(String url) {
this.url = url;
}
public int getStart() {
return start;
}
public void setStart(int start) {
this.start = start;
}
public int getEnd() {
return end;
}
public void setEnd(int end) {
this.end = end;
}
public int getFinished() {
return finished;
}
public void setFinished(int finished) {
this.finished = finished;
}
@Override
public String toString() {
return "ThreadInfo [id=" + id + ", url=" + url + ", start=" + start
+ ", end=" + end + ", finished=" + finished + "]";
}
}
再接着是不是该对数据库新建的表进行增删改相关的操作了呢，新建一个接口ThreadDAO如下：
package com.dingfang.org.sqlitedemo.db.dao;
import com.dingfang.org.sqlitedemo.entity.ThreadInfo;
import java.util.List;
/**
* ThreadInfo 数据访问接口
*/
public interface ThreadDAO
{
/**
* 插入线程信息
*/
public void insertThread(ThreadInfo threadInfo);
/**
* 删除线程信息
*/
public void deleteThread(String url, int thread_id);
/**
* 更新线程下载进度
*/
public void updateThread(String url, int thread_id, int finished);
/**
* 查询文件的线程信息
*/
public List<ThreadInfo> getThreads(String url);
/**
* 线程信息是否存在
*/
public boolean isExists(String url, int thread_id);
}
然后对上面的接口进行实现，新建ThreadDAOImpl类：
package com.dingfang.org.sqlitedemo.db.dao;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import com.dingfang.org.sqlitedemo.db.DBHelper;
import com.dingfang.org.sqlitedemo.entity.ThreadInfo;
import java.util.ArrayList;
import java.util.List;
/**
* 数据访问接口实现
*/
public class ThreadDAOImpl implements ThreadDAO {
private DBHelper mHelper = null;
public ThreadDAOImpl(Context context) {
mHelper = new DBHelper(context);
}
/**
* 增
* @param threadInfo
*/
@Override
public void insertThread(ThreadInfo threadInfo) {
SQLiteDatabase db = mHelper.getWritableDatabase();
db.execSQL("insert into thread_info(thread_id,url,start,end,finished) values(?,?,?,?,?)",
new Object[]{threadInfo.getId(), threadInfo.getUrl(),
threadInfo.getStart(), threadInfo.getEnd(), threadInfo.getFinished()});
db.close();
}
/**
* 删
* @param url
* @param thread_id
*/
@Override
public void deleteThread(String url, int thread_id) {
SQLiteDatabase db = mHelper.getWritableDatabase();
db.execSQL("delete from thread_info where url = ? and thread_id = ?",
new Object[]{url, thread_id});
db.close();
}
/**
* 改
* @param url
* @param thread_id
* @param finished
*/
@Override
public void updateThread(String url, int thread_id, int finished) {
SQLiteDatabase db = mHelper.getWritableDatabase();
db.execSQL("update thread_info set finished = ? where url = ? and thread_id = ?",
new Object[]{finished, url, thread_id});
db.close();
}
/**
* 查
* @param url
* @return
*/
@Override
public List<ThreadInfo> getThreads(String url) {
List<ThreadInfo> list = new ArrayList<ThreadInfo>();
SQLiteDatabase db = mHelper.getWritableDatabase();
Cursor cursor = db.rawQuery("select * from thread_info where url = ?", new String[]{url});
while (cursor.moveToNext()) {
ThreadInfo threadInfo = new ThreadInfo();
threadInfo.setId(cursor.getInt(cursor.getColumnIndex("thread_id")));
threadInfo.setUrl(cursor.getString(cursor.getColumnIndex("url")));
threadInfo.setStart(cursor.getInt(cursor.getColumnIndex("start")));
threadInfo.setEnd(cursor.getInt(cursor.getColumnIndex("end")));
threadInfo.setFinished(cursor.getInt(cursor.getColumnIndex("finished")));
list.add(threadInfo);
}
cursor.close();
db.close();
return list;
}
/**
* 判断是否存在
* @param url
* @param thread_id
* @return
*/
@Override
public boolean isExists(String url, int thread_id) {
SQLiteDatabase db = mHelper.getWritableDatabase();
Cursor cursor = db.rawQuery("select * from thread_info where url = ? and thread_id = ?", new String[]{url, thread_id + ""});
boolean exists = cursor.moveToNext();
cursor.close();
db.close();
return exists;
}
}
到此，所有的数据库创建，表创建，以及数据库表的访问操作就完成了。下面来看一下使用 。
新建一个MainActivity：
package com.dingfang.org.sqlitedemo;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.TextView;
import com.dingfang.org.sqlitedemo.db.dao.ThreadDAO;
import com.dingfang.org.sqlitedemo.db.dao.ThreadDAOImpl;
import com.dingfang.org.sqlitedemo.entity.ThreadInfo;
import java.util.List;
public class MainActivity extends AppCompatActivity {
private TextView textView;
ThreadDAO dao;//数据库操作类
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
initView();
}
private void initView() {
textView = (TextView) findViewById(R.id.content);
dao = new ThreadDAOImpl(this);
}
public void onBtnClicked(View v) {
switch (v.getId()) {
case R.id.save:
onSaveClicked();
break;
case R.id.fetch:
onFetchClicked();
break;
}
}
public void onSaveClicked() {
ThreadInfo info = new ThreadInfo(2, "http:www.ttreader.com", 0, 1024 * 10, 1234);
dao.insertThread(info);
}
public void onFetchClicked() {
List<ThreadInfo> infos = dao.getThreads("http:www.ttreader.com");
String finishedStr = "";
for (ThreadInfo item : infos) {
finishedStr += item.getFinished();
}
textView.setText("已完成进度：" + finishedStr);
}
}
activity_main.xml文件很简单，为了理解上面的代码，还是贴出来如下：
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="match_parent">
<TextView
android:id="@+id/content"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_margin="5dp"
android:text="Hello World!" />
<Button
android:id="@+id/save"
android:onClick="onBtnClicked"
android:text="存"
android:layout_width="match_parent"
android:layout_height="wrap_content" />
<Button
android:id="@+id/fetch"
android:onClick="onBtnClicked"
android:text="取"
android:layout_width="match_parent"
android:layout_height="wrap_content" />
</LinearLayout>
都是很简单的操作，这里就不做过多解释了，可以动手试试了。
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