Android 中数据存储的基本使用

1. SharedPreferences

SharedPreferencesActivity 文件

package com.example.hello.dataStorage;

import androidx.appcompat.app.AppCompatActivity;

import android.annotation.SuppressLint;
import android.content.SharedPreferences;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;

import com.example.hello.R;

public class SharedPreferencesActivity extends AppCompatActivity {
    
    

    // 声明
    private EditText etContent;
    private TextView tvShowContent;
    private Button btnSave, btnShow;
    private SharedPreferences sharedPreferences;
    private SharedPreferences.Editor editor;

    @SuppressLint("CommitPrefEdits")
    @Override
    protected void onCreate(Bundle savedInstanceState) {
    
    
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_shared_preferences);

        sharedPreferences = getSharedPreferences("", MODE_PRIVATE);
        editor = sharedPreferences.edit();
        // 获取
        etContent = findViewById(R.id.et_content);
        tvShowContent = findViewById(R.id.tv_show_content);
        btnSave = findViewById(R.id.btn_save);
        btnShow = findViewById(R.id.btn_show);
        // 点击事件
        btnSave.setOnClickListener(v -> {
    
    
            editor.putString("name", etContent.getText().toString());
            // commit() 同步过程, apply() 异步过程.
            editor.apply();
        });
        btnShow.setOnClickListener(v -> {
    
    
            tvShowContent.setText(sharedPreferences.getString("name", ""));
        });
    }
}

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:padding="15dp"
    tools:context=".dataStorage.SharedPreferencesActivity">

    <EditText
        android:id="@+id/et_content"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:autofillHints=""
        android:hint="@string/inputContent"
        android:inputType="text" />

    <Button
        android:id="@+id/btn_save"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginTop="10dp"
        android:text="@string/save"
        android:textAllCaps="false" />

    <Button
        android:id="@+id/btn_show"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginTop="10dp"
        android:text="@string/show"
        android:textAllCaps="false" />

    <TextView
        android:id="@+id/tv_show_content"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginTop="10dp"
        android:hint="@string/showContent"
        android:gravity="center"/>

</LinearLayout>

在这里插入图片描述

2. File

Android 存储概念

2.1 内部存储

FileActivity 文件

package com.example.hello.dataStorage;

import androidx.appcompat.app.AppCompatActivity;

import android.annotation.SuppressLint;
import android.os.Bundle;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;

import com.example.hello.R;

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;

public class FileActivity extends AppCompatActivity {
    
    

    // 声明
    private EditText etContent;
    private TextView tvShowContent;
    private Button btnSave, btnShow;
    private final static String FILE_NAME = "test.txt";

    @SuppressLint("CommitPrefEdits")
    @Override
    protected void onCreate(Bundle savedInstanceState) {
    
    
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_file);

        // 获取
        etContent = findViewById(R.id.et_content);
        tvShowContent = findViewById(R.id.tv_show_content);
        btnSave = findViewById(R.id.btn_save);
        btnShow = findViewById(R.id.btn_show);
        // 点击事件
        btnSave.setOnClickListener(v -> {
    
    
            // .trim() 去除前后空格
            save(etContent.getText().toString().trim());
        });
        btnShow.setOnClickListener(v -> {
    
    
            tvShowContent.setText(read());
        });
    }

    /**
     * 存储数据
     *
     * @param content 存储内容
     */
    private void save(String content) {
    
    
        FileOutputStream fileOutputStream = null;
        try {
    
    
            fileOutputStream = openFileOutput(FILE_NAME, MODE_PRIVATE);
            fileOutputStream.write(content.getBytes());
        } catch (IOException e) {
    
    
            e.printStackTrace();
        } finally {
    
    
            if (fileOutputStream != null) {
    
    
                try {
    
    
                    fileOutputStream.close();
                } catch (IOException e) {
    
    
                    e.printStackTrace();
                }
            }
        }
    }

    /**
     * 读取数据
     *
     * @return 读取的内容
     */
    private String read() {
    
    
        FileInputStream fileIutputStream = null;
        try {
    
    
            fileIutputStream = openFileInput(FILE_NAME);
            byte[] bytes = new byte[1024];
            StringBuilder buffer = new StringBuilder();
            int len = 0;
            if ((len = fileIutputStream.read(bytes)) > 0) {
    
    
                buffer.append(new String(bytes, 0, len));
            }
            return buffer.toString();
        } catch (IOException e) {
    
    
            e.printStackTrace();
        } finally {
    
    
            if (fileIutputStream != null) {
    
    
                try {
    
    
                    fileIutputStream.close();
                } catch (IOException e) {
    
    
                    e.printStackTrace();
                }
            }
        }
        return null;
    }
}

activity_file 文件和 activity_shared_preferences 内容是一样的.

2.2 外部存储

外部存储路径的设置

File path= getExternalFilesDir(type);

type 可以为:
	1. null // 根目录
	2. Environment.DIRECTORY_MUSIC //创建一个 music 目录
	3. Environment.DIRECTORY_PODCASTS //创建一个 podcasts 目录
	4. Environment.DIRECTORY_RINGTONES //创建一个 ringtones 目录
	5. Environment.DIRECTORY_ALARMS //创建一个 alarms 目录
	6. Environment.DIRECTORY_NOTIFICATIONS //创建一个 notifications 目录
	7. Environment.DIRECTORY_PICTURES //创建一个 pictures 目录
	8. Environment#DIRECTORY_MOVIES //创建一个 movies 目录

package com.example.hello.dataStorage;

import androidx.appcompat.app.AppCompatActivity;

import android.annotation.SuppressLint;
import android.os.Bundle;
import android.os.Environment;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;

import com.example.hello.R;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;

public class FileActivity extends AppCompatActivity {
    
    

    // 声明
    private EditText etContent;
    private TextView tvShowContent;
    private Button btnSave, btnShow;
    private final static String FILE_NAME = "test.txt";

    @SuppressLint("CommitPrefEdits")
    @Override
    protected void onCreate(Bundle savedInstanceState) {
    
    
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_file);

        // 获取
        etContent = findViewById(R.id.et_content);
        tvShowContent = findViewById(R.id.tv_show_content);
        btnSave = findViewById(R.id.btn_save);
        btnShow = findViewById(R.id.btn_show);
        // 点击事件
        btnSave.setOnClickListener(v -> {
    
    
            // .trim() 去除前后空格
            save(etContent.getText().toString().trim());
        });
        btnShow.setOnClickListener(v -> {
    
    
            tvShowContent.setText(read());
        });
    }

    /**
     * 存储数据
     *
     * @param content 存储内容
     */
    @SuppressWarnings("ResultOfMethodCallIgnored")
    private void save(String content) {
    
    
        FileOutputStream fileOutputStream = null;
        try {
    
    
//            fileOutputStream = openFileOutput(FILE_NAME, MODE_PRIVATE);
            File file = new File(getExternalFilesDir(Environment.DIRECTORY_PICTURES), FILE_NAME);
            if (!file.exists()) {
    
    
                file.createNewFile();
            }
            fileOutputStream = new FileOutputStream(file);
            fileOutputStream.write(content.getBytes());
        } catch (IOException e) {
    
    
            e.printStackTrace();
        } finally {
    
    
            if (fileOutputStream != null) {
    
    
                try {
    
    
                    fileOutputStream.close();
                } catch (IOException e) {
    
    
                    e.printStackTrace();
                }
            }
        }
    }

    /**
     * 读取数据
     *
     * @return 读取的内容
     */
    private String read() {
    
    
        FileInputStream fileInputStream = null;
        try {
    
    
//            fileInputStream = openFileInput(FILE_NAME);
            File file = new File(getExternalFilesDir(Environment.DIRECTORY_PICTURES), FILE_NAME);
            fileInputStream = new FileInputStream(file);
            byte[] bytes = new byte[1024];
            StringBuilder buffer = new StringBuilder();
            int len = 0;
            if ((len = fileInputStream.read(bytes)) > 0) {
    
    
                buffer.append(new String(bytes, 0, len));
            }
            return buffer.toString();
        } catch (IOException e) {
    
    
            e.printStackTrace();
        } finally {
    
    
            if (fileInputStream != null) {
    
    
                try {
    
    
                    fileInputStream.close();
                } catch (IOException e) {
    
    
                    e.printStackTrace();
                }
            }
        }
        return null;
    }
}

开启权限

AndroidManifest.xml 文件内设置.

    <uses-permission
        android:name="android.permission.WRITE_EXTERNAL_STORAGE"
        android:requestLegacyExternalStorage="true" />

可以在 MainActivity 文件内设置.

// 申请权限
ActivityCompat.requestPermissions(this, new String[]{
    
    Manifest.permission.WRITE_EXTERNAL_STORAGE}, 1);

在这里插入图片描述

Android 中 数据存储的基本使用

Android 中 数据存储的基本使用

1. SharedPreferences

2. File

2.1 内部存储

2.2 外部存储

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Android 中数据存储的基本使用

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