Android学习笔记之数据持久化

• 文件存储

activity_mian.xml

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

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);
            }
        });
    }


}