android 数据对象 android基本数据类型

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mob6454cc73e9a6 2023-06-27 09:15:59

文章标签 android 数据对象 java android ide SQL 文章分类 代码人生

数据存储

1、SQLite数据库

SQLite是一款轻型的数据库，它的设计目标是嵌入式的,而且目前已经在很多嵌入式产品中使用了它，占用资源非常的低，支持Windows/Linux/Unix等主流的操作系统，同时跟很多程序语言相结合，还有ODBC接口，同样比起Mysql、PostgreSQL数据库管理系统来讲，处理速度比他们更快。

www.sqlite.com

一般数据类型采用固定的静态数据类型，而SQLite采用的是动态数据类型，会根据存入值自动判断。具备五种数据类型：

1、NULL:空值

2、INTEGER：带符号的整形，具体取决有存入数字的范围大小

3、REAL：浮点数字，存储8-byte IEEE浮点数

4、TEXT：字符串文本

5、BLOB：二进制对象

实际上，sqlite3也接受如下数据类型

smallint 16位元的整数

interger 32位元的整数

decimal（p,s）精确值和s大小的十进位整数,精确值p是指全部有几个数大小值。

s是指小数点有几位，没有特别指定，系统设为p=5,s=0;

float 32位元的实数

double 64位元的实数

char(n) n长度的字串,n不能超过254。

varchar(n)长度不固定且其最大长度为n的字串,n不能超过4000

graphic(n)和char(n)一样,单位是两个字元double-bytes，n不能超过127。

这个形态是为了支援两个字元长度的字体。

varhraphic(n)可变长度且最大长度为n的双字元字串,n不能超过2000

date包含年、月、日期

time包含时、分、秒

timestamp包含了年、月、日、时、分、秒、千分之一秒

datetime包含日期时间格式,格式2020-08-05

SQLiteHelper

1 基本sql

工具类帮助创建和管理数据库

public class DbOpenHelper extends SQLiteOpenHelper{
//数据库版本
private static final int VERSION = 1;
//数据名
private static final String DBNAME="data.db"

public DbOpenHelper(Context context){
super(context,DBNAME,null,VERSION)
//
}
//程序创建时执行，只执行一次
 @Override
 public void onCreate(SQLiteDatabase db){
    db.execSQL("create table t_student(id integer primary key,name varchar(20),age integer)")
 }
 //数据的备份和更新
  @Override
  public void onUpgrade(SQLiteDatabase db,int oldVersion,int newVersion){
  
  }

}

public class StudentDao{
private DbOpenHelper helper;
private SQLiteDatabase db;

public StudentDao(Context context){
  helper = new DdOpenHelper(context);
}

public void add(Student student){
  db=helper.getWritableDatabase();//不可写会抛出异常getReadableableDatabase()读写均可
  db.execSQL("insert into t_student(id,name,age) value(?,?,?)",new Object[]{student.getId(),student.getName(),student.getAge})
}
}

public Student find(int id){
 db = helper.getWritableDatabase();
 Cursor cursor = db.rawQuery("select id,name,age from t_student where id=?",new Object[]{String.valueOf(id)});
    if(cursor.moveToNext()){
        //cursor.getString(cursor.getColumnIndex("id"))
        return new Student(cursor.getInt(cursor.getColumnIndex("id")),cursor.getString(cursor.getColumnIndex("name")),cursor.getInt(cursor.getColumnIndex("age")));
    }
    return null;
}

public void delete(Integer...ids){
    if(ids.length>0){
        StringBuffer sb = new  StringBuffer();
        for(int i=0;i<ids.length;i++){
            sb.appends('?').append(',');
        }
        //删除最后的逗号
        sb.deleteCharAt(sb.length()-1);
        SQLiteDatabase database = helper.getWritableDatabase();
        database.execSQL("delete from t_student where id in("+sb+")"，(Object[] )ids)
    }
}

public List<Student> getScrollData(int start,int count){
    List<Student> students = new ArrayList<Student>();
    db = helper.getWritableDatabase();
    Cursor cursor = db.rawQuery("select * from t_student limit ?,?",new String[]{String.valueOf(start),String.valueOf(start+count)});
    while(cursor.moveToNext()){
        students.add(new Student(cursor.getInt(cursor.getColumnIndex("id")),cursor.getString(cursor.getColumnIndex("name")),cursor.getInt(cursor.getColumnIndex("age")));
    }
}


public long getCount(){
   db = helper.getWritableDatabase();
    Cursor cursor = db.rawQuery("select count(id) from t_student",null);
    if(cursor.moveToNext()){
        return cursor.getLong(0);
    }
    return 0;
}
    
}

2内置sql方法

public class StudentDao2{
private DbOpenHelper helper;
private SQLiteDatabase db;

public StudentDao2(Context context){
  helper = new DdOpenHelper(context);
}

public void add(Student student){
 db =helper.getWritableDatabase();
 ContentValues values = new ContentValues();
 values.put("id",student.getId());
 values.put("name",student.getName());
 values.put("age",student.getAge());
  //nullColumnHack:当values参数为空或者无内容，insert失败
  //为了防止这种情况，我们在此指定一个列名，如果插入行为为空行，
   //将指定列名值为null （表名,指定列,数据值）
  db.insert("t_student","id",values);
}
public void update(Student student){
 db =helper.getWritableDatabase();
 ContentValues values = new ContentValues();
 values.put("name",student.getName());
 values.put("age",student.getAge());
    //(table,values,whereClause,whereArgs)
 db.update("t_student",values,"id = ?",new String[]{String.valueOf(student.getId())})
}
    
    
public Student find(int id){
 db =helper.getWritableDatabase();
      //(table,column,selection,selectionArgs,groupBy,having,orderBy)
 Cursor cursor = db.query("t_student",new String[]{"id","name","age"},"id = ?",new String[]{String.valueOf(student.getId()),null,null,null);
  if(cursor.moveToNext()){
      return new Student(cursor.getInt(0),cursor.getString(1),cursor.getInt(2));
  }     
  return null;                                                                         
}

public void delete(Integer...ids){
    if(ids.length>0){
        StringBuffer sb = new  StringBuffer();
        String[] strPid = new String[ids.length]
        for(int i=0;i<ids.length;i++){
            sb.appends('?').append(',');
            strPid[i]=String.valueOf(ids[i]);
        }
        //删除最后的逗号
        sb.deleteCharAt(sb.length()-1);
        db = helper.getWritableDatabase();
        //(table,whereClause,whereArgs)
        db.delete("t_student","pid in ("+sb+")",strPid);
        
}

public List<Student> getScrollData(int start,int count){
      List<Student> students = new ArrayList<Student>();
       db = helper.getWritableDatabase();
    //(table,columns,)
    Cursor cursor = db.query("t_student",new String[]{"id","name","age"],null,null,null,null,"sid desc",start+","+count})
        while(cursor.moveToNext()){
           students.add(new Student(cursor.getInt(0),cursor.getString(1),cursor.getInt()));
        }
    return students;
}


public long getCount(){
    db = helper.getWritableDatabase();
    Cursor cursor = db.query("t_student",new String[]{"count(*)"},null,null,null,null,null);
    if(cursor.moveToNext()){
        return cursor.getLong(0);
    }
    return 0;
}

数据库升级,版本变更（更改表名，下次创新表，原表数据的备份后删除）

//数据的备份和更新
  @Override
  public void onUpgrade(SQLiteDatabase db,int oldVersion,int newVersion){
    String tempTable ="temp_student";
    db.execSQL("alert table"+STUDENT+"rename to "+tempTable);
    db.execSQL("create table"+STUDENT+"(id integer primary key,name varchar(20),age integer,sex varchar(10))");
    String sql = "insert into "+STUDENT+"(name,age,sex) select name,age,'男' from"+tempTable;
    db.execSQL(sql)
  }

2、文件

1、openFileOutput(String name,int mode)写

name,文件名称，不能包含分隔符"/"，如果不存在，自动创建在

/data/data/<package_name>/files目录下

mode，操作模式 MODE_APPEND内容末尾追加 MODE_PRIVATE仅能被程序访问

MODE_WORLD_READABLE 文件允行被其他应用程序读

MODE_WORLD-WRITEABLE文件允行被其他应用程序写

2、openFileInput(String name)读

public class FileService{
   public void save(OutputStream out,String content) throw IOException{
     out.write(content.getByte());
     out.close();
   }
   public String read(InputStream in)throw IOException{
   ByteArrayOutputStream out = new ByteArrayOutputStream();
   byte[] buffer = new byte[1024];
   int len;
   while((len=in.read(buffer)!=-1){
    out.write(buffer,0,len);
   }
    byte[] data = out.toByteArray();
   out.close();
   in.close();
   return new String(data);
   }
}

3、Shared Preferences

保存用户配置信息(触发事件中书写)

//editName editAge…EditText控件

SharedPreferences pres = MainActivity.this.getSharedPreferences("kuka",mode);
Editor editor = pres.edit();
editor.putString("name",editName.getText().toString());
editor.putInt("age",Integer.valueOf(editAge));
//需要提交
editor.commit();
Toast.makeText(MainActivity.this,"保存成功",Toast.LENGTH_LONG).show();

String name =pres.getString("name","null");
int age =pres.getInt("age",0);

文件目录/data/data/<package_name>/shared_prefs/kuka.xml

4、内容提供者（Content Providers）

Content Providers 是所有应用程序之间数据存储和检索的一个桥梁，作用是使得各个应用程序之间实现数据共享。它是应用程序间共享数据的唯一方法。在Android没有一块公共的所有程序都能访问的数据存储地方。

数据模型/URI

数据模型类似表格，每一行代表一条数据，查询返回cursor对象

URI,每一个content provider有一个公有URI，该URI用于识别它所代表的数据集合。所有的URI以字符串"content://"开始。

何时使用

增删改查

query()、insert()、update()、delete()、getType()

protected void add(int type){
ContentResolver contentResolver = getContentResolver();
Uri uri = null;
ContentValues values = new ContentValues();
switch(type){
case ONE:
     uri =Uri.parse("content://com.szy.provider.studentprovider/student");
     values.put("name","libai");
     values.put("age","100");
     contentResolver.insert(url,values);
     break;
case TWO:
     uri =Uri.parse("content://com.szy.provider.studentprovider/student/1");
     values.put("name","dufu");
     values.put("age","101");
     contentResolver.insert(url,values);
     break;
}
}

one与two均插入数据

插入之后分别为content://com.szy.provider.studentprovider/student/1

content://com.szy.provider.studentprovider/student/2

与初始提供的末尾数字无关

protected void update(int type){
ContentResolver contentResolver = getContentResolver();
Uri uri = null;
ContentValues values = new ContentValues();
String where="";
String [] selectionArgs=null;
switch(type){
case ONE:
     uri =Uri.parse("content://com.szy.provider.studentprovider/student");
     values.put("name","Updated");
     values.put("age","23");
     where = "id =  ?";
     selectionArgs=new String[]{"1"};
     contentResolver.update(url,values,where,selectionArgs);
     break;
case TWO:
     uri =Uri.parse("content://com.szy.provider.studentprovider/student/2");
     values.put("name","Updated");
     values.put("age","23");
     contentResolver.update(url,values,where,selectionArgs);
     break;
}
}

one更新时指定条件，two末尾有主键id更新时可以不指定条件。

protected void query(int type){
ContentResolver contentResolver = getContentResolver();
Uri uri = null;
String[] projection = new String[]{"id","name","age"};
String selection = "";
String [] selectionArgs=null;
String sortOrder = "";
Cursor cursor =null;

switch(type){
case ONE:
     uri =Uri.parse("content://com.szy.provider.studentprovider/student");
     selection = "id < ?";
     selectionArgs=new String[]{"3"};
     contentResolver.query(url,projection,selection,selectionArgs,sortOrder);
     while(cursor.moveToNext()){
     Log.i("TAG","id="+cursor.getInt(0)+"name="+cursor.getString(1))
     }
     break;
case TWO:
     uri =Uri.parse("content://com.szy.provider.studentprovider/student/1");
     contentResolver.query(url,projection,selection,selectionArgs,sortOrder);
       while(cursor.moveToNext()){
     Log.i("TAG","id="+cursor.getInt(0)+"name="+cursor.getString(1))
     }
     break;
}
}

protected void delete(int type){
ContentResolver contentResolver = getContentResolver();
Uri uri = null;
String where = "";
String [] selectionArgs=null;


switch(type){
case ONE:
     uri =Uri.parse("content://com.szy.provider.studentprovider/student");
     where = "id in (?,?)";
     selectionArgs=new String[]{"1","2"};
     contentResolver.delete(url,where,selectionArgs);
     break;
case TWO:
     uri =Uri.parse("content://com.szy.provider.studentprovider/student/1");
     contentResolver.delete(url,where,selectionArgs);
     break;
}
}

创建内容提供者步骤

1、定义一个继承ContentProvider的类

2、声明一个Uri类型的常量CONTENT_URI

3、实现query()、insert()、update()、delete()、getType()、onCreate()

4、在AndroidManifest.xml文件进行声明

public class StudentContentProvider extends ContentProvider{
private DBOpenHelper dbOpenHelper;
private final static int ONE=1;
private final static int TWO=2;
private final static String AUTHORITY ="com.szy.provider.studentprovider";
private static final UriMatcher sMatcher = new UriMatcher(UriMatcher.NO_MATCH);
static{
//content://com.szy.provider.studentprovider/student
sMatcher.addURI(AUTHORITY,"student",ONE);
//content://com.szy.provider.studentprovider/student/#
sMatcher.addURI(AUTHORITY,"student/#",TWO);
}
    @Override
   public boolean  OnCreate(){
        dbOpenHelper = new DBOpenHelper(this.Context());
        return true;
   }
    @Override
   public Cursor query(Uri uri,String[] projection,String selection,String[] selectionArgs,String sortOrder){
       SQLiteDatabase db = dbOpenHelper.getReadableDatabase();
       switch(sMatcher.match(uri)){
           case ONE:
               return db.query("t_studnet",projection,selection,selectionArgs,null,null,sortOrder);
           case TWO:
               long pid =ContentUri.parseId(uri);
               String where=TextUtils.isEmpty(selection)?"id=?":selection+"and id=?";
               String[] params = new String[]{String.valueOf(pid)};
               if(!TextUtils.isEmpty(selection)&&selectionArgs !=null){
                   params = new String[selectionArgs.length+1];
                   for(int i=0;i<selectionArgs.length;i++){
                       params[i]=selectionArgs[i];
                   }
               }
               return db.query("t_student",projection,where,params,null,null,sortOrder);
       }
   }
       @Override
   public Uri insert(Uri uri,ContentValues values){
       SQLiteDatabase db = dbOpenHelper.getReadableDatabase();
       long pid=0;
       switch(sMatcher.match(uri)){
           case ONE:
               pid=db.insert("t_student","name",values);
               return ContentUtils.withAppendedId(uri,pid);
           case TWO:
                pid=db.insert("t_student","name",values);
               String path=uri.toString();
               return Uri.parse(path.subString(0,path.lastIndexOf('/')+1)+pid);
       }
   }
       @Override
   public int  update(Uri uri,ContentValues values,String selection,String[] selectionArgs){
       SQLiteDatabase db = dbOpenHelper.getReadableDatabase();
       int count=0;
       switch(sMatcher.match(uri)){
       //自定义逻辑合理即可
       }
   }
    public String getType(Uri uri){
        switch(sMatcher.match(uri)){
            case ONE:
                return "vnd.android.cursor.dir/personProvider.person";
            case TWO:
               return "vnd.android.cursor.item/personProvider.person";       
        }
    }
}

5、网络

模拟Http请求

10.0.2.2 android模拟器请求电脑url地址

清单文件加入网络访问权限

GET请求方式

GET方式是通过把参数键值对附加在url后面传递的，在服务器端可以直接读取，效率较高，但缺乏安全性，也无法处理复杂的数据，长度有限制。用于传递简单参数。

POST请求方式

Post方式是将参数打包在http报头中传输，可以是二进制的，便于传送较大些的数据，安全性相对高，效率会受到影响。

HttpURLConnection方式

public class BasicHttpClient{
  private static final int TIME_OUT = 1000*6;//超时
  private static final String METHOD_POST="POST";
  private static final String METHOD_GET="GET";
  private static final int HTTP_OK=200;
  
public String httpGet(String urlStr){
  URI uri = null;
  HttpURLConnection conn =null;
  InputStream instream = null;
  String response = null;
  try{
      url = new  URL(urlStr);
      //设置url参数
      conn =(HttpURLConnection)url.openConnection();
      conn.setDoInput(true);
      conn.setConnectTimeout(TIME_OUT);
      conn.setRequestMethod(METHOD_GET);
      conn.setRequestProperty("accept","*/*");
      //连接，获得返回码
      conn.connect();
      int responseCode = conn.getResponseCode();
      if(responseCode == HTTP_OK){
          instream = conn.getInputStream();
          response = getResponse(instream);
      }else{
          response = "返回码："+responseCode;
      }catch(Exception e){
          e.printStackTrace();
      }finally{
          conn.disconnect();
      }
      return response;
  }
  }
    
public String httpPost(String urlStr,String params){
  byte[] data = params.getBytes();
  URI uri = null;
  HttpURLConnection conn =null;
  InputStream instream = null;
  String response = null;
  try{
      url = new  URL(urlStr);
      //设置url参数
      conn =(HttpURLConnection)url.openConnection();
      conn.setDoInput(true);
      conn.setOutInput(true);
      conn.setUseCaches(false);
      conn.setConnectTimeout(TIME_OUT);
      conn.setRequestMethod(METHOD_POST);
      conn.setRequestProperty("Connection","Keep-Alive");
      conn.setRequestProperty("Charset","UTF-8");
      conn.setRequestProperty("Content-Length",String.valueOf(data.length));
        conn.setRequestProperty("Content-Type","application/x-www-form-urlencoded");
      conn.connect();
      DataOutputStream outputStream = new DataOutputStream(conn.getOutputStream());
      outputStream.write(data);
      //将内容推到缓冲
      outputStream.flush();
      outputStream.close();
      int responseCode = conn.getResponseCode();
      if(responseCode == HTTP_OK){
          instream = conn.getInputStream();
          response = getResponse(instream);
      }else{
          response = "返回码："+responseCode;
      }catch(Exception e){
          e.printStackTrace();
      }finally{
          conn.disconnect();
      }
      return response;
  }
  }
}

使用HttpClient方式

public String httpGet(String url){
   String response = null;
   HttpClient httpclient = new DefaultHttpClient();
   HttpClient httpGet = new HttpGet(url);
   HttpResponse httpResponse;
   try{
   httpResponse = httpclient.execute(httpGet);
   int statusCode = httpResponse.getStatusLine().getStatusCode();
   if(statusCode==HttpStatus.SC_OK){
   response = EntityUtils.toString(httpResponse.getEntity());
   }else{
   response="返回码"+statusCode;
   }
   }catch(Exception e){
   e.printStackTrace();
   }
   return response;
   }
}

public String httpPosst(String url,List<NameValuePair> params){
   String response = null;
   HttpClient httpclient = new DefaultHttpClient();
   HttpClient httpPost = new HttpPost(url);
   try{
   httppost.setEntity(new UrlEncodedFormEntity(params,HTTP.UTF_8));
   HttpResponse httpResponse = httpclient.execute(httppost);
   int statusCode = httpResponse.getStatusLine().getStatusCode();
   if(statusCode==HttpStatus.SC_OK){
   response = EntityUtils.toString(httpResponse.getEntity());
   }else{
   response="返回码"+statusCode;
   }
   }catch(Exception e){
   e.printStackTrace();
   }
   return response;
   }
}

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