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Android开发-java版：data的存取和SharedPreferences

news 2025/11/14 16:09:40

一、字节流和字符流的存储和读取

1、存储Data到文件中

代码如下，我们逐行解释：

1.创建editText示例，并绑定布局文件中的控件

2.重写onDestroy方法，保证在活动销毁前一定会调用onDestroy里的方法，获取在editText控件中输入的内容，然后调用save()方法

3.先通过openFileOutput()方法能够得到一个FileOutputStream对象，然后借助它构建一个OutputStreamWriter对象，然后使用OutputStreamWriter构建出BufferedWriter对象，然后就可以通过BufferedWriter来将文本写到文件中了

Context类中提供了一个openFIleOutPut()方法，用于将数据存储到指定文件中。

包含两个参数，第一个参数是文件名，第二个参数是文件的操作模式

MODE_PRIVATE：默认的操作模式，写入的内容会覆盖原文件内容

MODE_APPEND：表示如果文件已经存在，就往文件里追加内容，不存在就创建文件

public class MainActivity extends AppCompatActivity {private EditText editText;@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);editText = (EditText) findViewById(R.id.editText);}protected void onDestroy(){super.onDestroy();String input = editText.getText().toString();save(input);}private void save(String input){FileOutputStream out = null;BufferedWriter writer = null;try {out = openFileOutput("data", Context.MODE_PRIVATE);writer = new BufferedWriter(new OutputStreamWriter(out));writer.write(input);}catch (IOException e ){e.printStackTrace();}finally {try {if(writer != null){writer.close();}}catch (IOException e){e.printStackTrace();}}}

2、从文件中读取Data

对比存储，新增了load()方法

1.首先通过openFileInput()收到了一个FileInputStream对象，然后构建出了InputStreamReader对象，然后用InputStreamReader构建出了BufferedReader对象，然后使用BufferedReader一行行读取，把文件中的内容全部读取出来并放在StringBuilder对象中，返回内容

2.在onCreate()方法中调用load()方法读取文件中存储的文本内容，如果不为null，则调用EditText的setText()方法将内容填充到EditText里，并调用setSelection()方法将光标移动到文本末尾，弹出还原成功的提示

public class MainActivity extends AppCompatActivity {private EditText editText;@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);editText = (EditText) findViewById(R.id.editText);String inputText = load();if(!TextUtils.isEmpty(inputText)){editText.setText(inputText);editText.setSelection(inputText.length());Toast.makeText(this,"Restoring succeeded",Toast.LENGTH_LONG).show();}}protected void onDestroy(){super.onDestroy();String input = editText.getText().toString();save(input);}private void save(String input){FileOutputStream out = null;BufferedWriter writer = null;try {out = openFileOutput("data", Context.MODE_PRIVATE);writer = new BufferedWriter(new OutputStreamWriter(out));writer.write(input);}catch (IOException e ){e.printStackTrace();}finally {try {if(writer != null){writer.close();}}catch (IOException e){e.printStackTrace();}}}private String load(){FileInputStream in = null;BufferedReader reader = null;StringBuffer content = new StringBuffer();try {in = openFileInput("data");reader = new BufferedReader(new InputStreamReader(in));String line = "";while ((line = reader.readLine()) != null){content.append(line);}} catch (IOException e) {e.printStackTrace();}finally {try {if(reader != null){reader.close();}}catch (IOException e){e.printStackTrace();}}return content.toString();}
}

二、SharedPreferences的存储和读取

1.SharedPreferences的存储

SharedPreferences是使用键值对的方式来存储数据的，想用SharedPreferences存储数据，首先要获取SharedPreferences对象。

使用Context类中的getSharedPerences方法

此方法接收两个参数，第一个用于指定SharedPreferences文件的名称，不存在则创建一个，第二个参数用于指定操作模式，目前只能选MODE_PRIVATE这一种模式，是默认操作模式，表示只有当前程序才可以对这个SharedPreferences文件进行读写。

public class MainActivity2 extends AppCompatActivity {@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main2);Button button = (Button) findViewById(R.id.button);button.setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View v) {SharedPreferences.Editor editor = getSharedPreferences("data",MODE_PRIVATE).edit();editor.putString("name","Tom");editor.putInt("age",28);editor.putBoolean("marred",false);editor.apply();}});}
}

2.SharedPreferences的读取

一系列的put存储方法对应着一系列的get获取方法

public class MainActivity2 extends AppCompatActivity {@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main2);Button button = (Button) findViewById(R.id.button);Button button1 = (Button) findViewById(R.id.button1);button1.setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View v) {SharedPreferences pref = getSharedPreferences("data",MODE_PRIVATE);String name = pref.getString("name","");int age =pref.getInt("age",0);boolean married = pref.getBoolean("married",false);Log.d("MainActivity","name is"+name);Log.d("MainActivity","age is"+ age);Log.d("MainActivity","married is"+married);}});button.setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View v) {SharedPreferences.Editor editor = getSharedPreferences("data",MODE_PRIVATE).edit();editor.putString("name","Tom");editor.putInt("age",28);editor.putBoolean("marred",false);editor.apply();}});}
}

三、记住密码（实践）

在上一篇代码都基础上修改，详情：

Android开发-java版：BroadcastReceiver广播-CSDN博客

增加内容：

1.类结构和变量声明

2.初始化pref和绑定布局中的checkBox组件

3.在onCreate里，读取保存的登录信息，isRemember为true，读取账号和密码

4.在登录方法里，如果选择了“记住密码”，则保存账号和密码

完整代码如下：

public class LoginActivity extends BaseActivity {private SharedPreferences pref;private SharedPreferences.Editor editor;private EditText accountEdit;private EditText passwordEdit;private Button login;private CheckBox remember;@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_login);String preferenceName = getPackageName() + "_preferences";Log.d("PreName",preferenceName);pref = getSharedPreferences(preferenceName,MODE_PRIVATE);accountEdit = (EditText) findViewById(R.id.accountEdit);passwordEdit = (EditText) findViewById(R.id.passwordEdit);remember = (CheckBox) findViewById(R.id.checkbox);login = (Button) findViewById(R.id.login);boolean isRemember = pref.getBoolean("remember_password",false);if(isRemember){String account = pref.getString("account","");String password = pref.getString("password","");accountEdit.setText(account);passwordEdit.setText(password);remember.setChecked(true);}login.setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View v) {String account = accountEdit.getText().toString();String password = passwordEdit.getText().toString();if(account.equals("admin")&&password.equals("123456")){editor = pref.edit();if(remember.isChecked()){editor.putBoolean("remember_password",true);editor.putString("account",account);editor.putString("password",password);}else {editor.clear();}editor.apply();Intent intent = new Intent(LoginActivity.this, MainActivity2.class);startActivity(intent);finish();}else {Toast.makeText(LoginActivity.this,"错误",Toast.LENGTH_LONG).show();}}});}
}

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