Android学习笔记之数据持久化

文件存储

activity_mian.xml

<?xml version="1.0" encoding="utf-8"?>

修改MainActivity

package com.syc.androidlearning;import androidx.appcompat.app.AppCompatActivity;import android.content.Context;import android.os.Bundle;import android.text.TextUtils;import android.widget.EditText;import android.widget.Toast;import java.io.BufferedReader;import java.io.BufferedWriter;import java.io.FileInputStream;import java.io.FileNotFoundException;import java.io.FileOutputStream;import java.io.IOException;import java.io.InputStreamReader;import java.io.OutputStreamWriter;public class MainActivity extends AppCompatActivity {    private EditText editText;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        editText = findViewById(R.id.edit);        String inputText = load();        if (!TextUtils.isEmpty(inputText)){            editText.setText(inputText);            Toast.makeText(this,"restoring succeed",Toast.LENGTH_SHORT).show();        }    }    private String load() {        FileInputStream in = null;        BufferedReader reader = null;        StringBuilder content = new StringBuilder();        try {            in = openFileInput("data");            reader = new BufferedReader(new InputStreamReader(in));            String line = "";            while ((line = reader.readLine()) != null) {                content.append(line);            }        }        catch (FileNotFoundException e) {            e.printStackTrace();        } catch (IOException e) {            e.printStackTrace();        } finally {            if (reader != null){                try {                    reader.close();                } catch (IOException e) {                    e.printStackTrace();                }            }        }        return content.toString();    }    @Override    protected void onDestroy() {        super.onDestroy();        String input = editText.getText().toString();        save(input);    }    public void save(String input) {        FileOutputStream outputStream = null;        BufferedWriter writer = null;        try {            outputStream = openFileOutput("data", Context.MODE_PRIVATE);            writer = new BufferedWriter(new OutputStreamWriter(outputStream));            writer.write(input);        } catch (FileNotFoundException e) {            e.printStackTrace();        } catch (IOException e) {            e.printStackTrace();        } finally {            if (writer != null) {                try {                    writer.close();                } catch (IOException e) {                    e.printStackTrace();                }            }        }    }}

SharedPreference存储

SharedPreference使用键值对存储数据，他比文件存储更加简单。

修改activity_mian.xml

<?xml version="1.0" encoding="utf-8"?>

修改ActivityMain文件

package com.syc.androidlearning;import androidx.appcompat.app.AppCompatActivity;import android.content.Context;import android.content.SharedPreferences;import android.os.Bundle;import android.text.TextUtils;import android.util.Log;import android.view.View;import android.widget.Button;import android.widget.EditText;import android.widget.Toast;import java.io.BufferedReader;import java.io.BufferedWriter;import java.io.FileInputStream;import java.io.FileNotFoundException;import java.io.FileOutputStream;import java.io.IOException;import java.io.InputStreamReader;import java.io.OutputStreamWriter;public class MainActivity extends AppCompatActivity {    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        Button saveData = findViewById(R.id.save);        Button restoreData = findViewById(R.id.restore);        saveData.setOnClickListener(new View.OnClickListener() {            @Override            public void onClick(View v) {                SharedPreferences.Editor editor = getSharedPreferences("data", MODE_PRIVATE).edit();                editor.putString("name", "SYC");                editor.putInt("age", 24);                editor.apply();            }        });        restoreData.setOnClickListener(new View.OnClickListener() {            @Override            public void onClick(View v) {                SharedPreferences preferences = getSharedPreferences("data", MODE_PRIVATE);                String name = preferences.getString("name", "");                int age = preferences.getInt("age", 0);                Log.d("MainActivity", "name is " + name + "age is " + age);            }        });    }}

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