数据存储（sharedPreferences,内部存储，外部存储，SQLite数据库，网络存储）

1、SharedPreferences xml存储

xml布局文件

<TextView
        android:id="@+id/textview"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />

    <EditText
        android:id="@+id/edittext"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="输入内容" />

    <Button
        android:id="@+id/button_write"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="写数据" />

    <Button
        android:id="@+id/button_read"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="读数据" />

在activity中对按钮建立点击事件

private void write() {//写入数据的方法
        SharedPreferences preferences = getSharedPreferences("preferences_write",MODE_PRIVATE);
        SharedPreferences.Editor  editor = preferences.edit();
        editor.putString("edittext_input",mEdittext.getText().toString());//从edittext_input写入
        editor.commit();
        mEdittext.setText("");
    }

    private void read() {//读数据的方法
        SharedPreferences preferences = getSharedPreferences("preferences_write",MODE_PRIVATE);//文件名称要相同
        String content = preferences.getString("edittext_input","没有写东西");//对应从edittext_input读出，"没有写东西"这是默认值
        mTextview.setText(content);
    }

2、内部存储

<Button
        android:id="@+id/button_cache"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="写入数据缓存到file" />//写到file文件夹下

    <Button
        android:id="@+id/button_readcache"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="读取数据缓存" />
    <Button
        android:id="@+id/button_cachedir"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="写入数据缓存到cache" />//写到cache文件夹下

在activity中

private void writecache() {//在file文件夹下hellocache出写入缓存数据“你好”
        try {
            FileOutputStream outputStream = openFileOutput("hellocache",MODE_PRIVATE);
            PrintWriter writer = new PrintWriter(new OutputStreamWriter(outputStream));
            writer.write("你好");
            writer.flush();
            writer.close();
            outputStream.close();
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
    private void readcache() {//读取hellocache文件的缓存数据
        try {
            FileInputStream is = openFileInput("hellocache");
            BufferedReader reader = new BufferedReader(new InputStreamReader(is));
            String  line = reader.readLine();
            while(line!=null){
               mTextview.setText(line);
                line = reader.readLine();
            }
            reader.close();
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

 private void writecachedir() {
        File file = new File(getCacheDir(),"helloworld.txt");
        if(!file.exists()){//如果cache文件夹下没有该文件，则创建一个名为helloworld的文件
            try {
                file.createNewFile();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        try {//在文件中写入内容
            FileOutputStream outputStream = new FileOutputStream(file);
            PrintWriter writer = new PrintWriter(new OutputStreamWriter(outputStream));
            writer.write("你好,我是最近的缓存");
            writer.flush();
            writer.close();
            outputStream.close();
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

3、外部存储

注意在这里要写权限

在minafest中

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.my.administrator.sharedpreferences" >
   //这个是插拔式扩展卡的读写权限 
<uses-permission android:name="android.permission.MOUNT_UNMOUNT_FILESYSTEMS">
//这个是手机本身存储的读写权限
</uses-permission>
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"></uses-permission>

写入到本地磁盘

private void writecachesd() {
        File file = new File(Environment.getExternalStorageDirectory(),"helloword.txt");//在mnt/shell/emulated/0 文件夹下的helloworld问件
        if(!file.exists()){
            try {
                file.createNewFile();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        try {
            FileOutputStream outputStream = new FileOutputStream(file);
           outputStream.write("本地缓存".getBytes());
            outputStream.flush();
            outputStream.close();
            outputStream.close();//也可以和上面的写入方法一样去写
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

4SQLite数据库

1、创建一个数据库

<Button//layout下布局文件中的按钮
      android:id="@+id/button_sql"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:text="创建数据库"/>

2、写一个MySQliteOpenHelpter类继承SQLiteOpenHelper

public class MySQliteOpenHelpter extends SQLiteOpenHelper {
    public MySQliteOpenHelpter(Context context, String name, SQLiteDatabase.CursorFactory factory, int version) {
        super(context, name, factory, version);
    }
    public MySQliteOpenHelpter(Context context, String name){
        this(context,name,null,1);//创建数据库
    }
                               @Override
    public void onCreate(SQLiteDatabase db) {
      db.execSQL("create table if not exists student(id integer primary key autoincrement,name varchar(20),password varchar(20))");//创建表table
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {

    }
}

3、在Mainactivity中创建点击事件

@Override
    public void onClick(View v) {
        switch (v.getId()) {
            case R.id.button_sql:
MySQliteOpenHelpter helpter = new MySQliteOpenHelpter(getApplicationContext(), "MY_FIRST_DB.db");
      SQLiteDatabase  database = helpter.getWritableDatabase();
                Toast.makeText(MainActivity.this, "创建了数据库", Toast.LENGTH_SHORT).show();
                break;

运行后会在包下创建database文件夹，下有”MY_FIRST_DB.db数据库，可导出查看。

4、插入数据

//插入按钮
 <Button
        android:id="@+id/button_insert"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="插入数据"/>
___________________________________________________
case R.id.button_insert:
                ContentValues value = new ContentValues();
                value.put("name", "张三");
                value.put("password", "121121");
                database.insert("student", null, value);//insert方法插入数据
                break;

运行后在包下database文件夹中的”MY_FIRST_DB.db数据库，将插入上面的数据”张三“。

5.删除数据

case R.id.button_delete:
                database.delete("student","name=?",new String[]{mEditTextName.getText().toString()});
                Toast.makeText(MainActivity.this, "删除了这条数据", Toast.LENGTH_SHORT).show();

6、更新数据

case R.id.button_update:
                ContentValues values = new ContentValues();
                values.put("password","aaa");
                database.update("student", values, "name=?", new String[]{mEditTextName.getText().toString()});
                Toast.makeText(MainActivity.this, "修改了这条数据的密码", Toast.LENGTH_SHORT).show();
                break;

7、查询数据

case R.id.button_select:
                Cursor cursor=database.query("student", null, null, null, null, null, "id DESC", "2 ,2");//DESC是倒序，“2，2”偏移2个，查询2个
//      查询全部数据时       database.rawQuery("select * from student", null);
                cursor.moveToFirst();
                while(!cursor.isAfterLast()){
                    String name=cursor.getString(cursor.getColumnIndex("name"));
                    String password = cursor.getString(cursor.getColumnIndex("password"));
                    Log.d("cursor","用户名"+name+" 密码 "+password);
                    Toast.makeText(MainActivity.this,"用户名"+name+"密码 "+password, Toast.LENGTH_SHORT).show();
                    cursor.moveToNext();
                }
                break;