Le Tutoriel de Android External Storage

Android External Storage
Par exemple, lire et écrire des fichiers sur un stockage externe
Annexe: Conception de l'interface

1. Android External Storage

Android External Storage: est un endroit pour stocker des données externes d'Android, les fichiers de données que vous stockez ici ne sont pas appliqués par le système pour appliquer la sécurité.

Il existe généralement 2 types de stockage externe (external storage).

Stockage externe fixe: généralement appelé disque dur d'un téléphone.
Stockage externe amovible (Removeable Storage): telle SD Card.

En utilisant les méthodes statiques de la classe Environment, vous pouvez obtenir les informations de répertoire du stockage externe.

Voici le tableau des résultats lors de l'exécution sur l'émulateur (emulator):

Method	Returns
getDataDirectory()	/data
getDownloadCacheDirectory()	/cache
getExternalStorageState()	mounted
getExternalStoragePublicDirectory(Environment.Music):	/storage/emulated/0/Music
getDownloadCacheDirectory()	/cache
getRootDirectory()	/system

Pour lire et écrire des données sur un stockage externe, vous devez configurer AndroidManifest.xml, ajoutez:

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

Avec Android Level> = 23 pour lire et écrire des données sur un périphérique de stockage externe, vous devez demander à l'utilisateur en utilisant le code. (Voir plus dans l'exemple.)

Android API Level < 29

Avec Android API Level <29, les applications peuvent stocker ses données sur un stockage externe (External Storage), en particulier dans le dossier ci-dessous (ou sous-dossiers).

if (android.os.Build.VERSION.SDK_INT < 29) {

     // ==>  /storage/emulated/0    (Emulator)
     File dir = Environment.getExternalStorageDirectory();

}

La méthode de stockage mentionnée ci-dessus peut provoquer des conflits entre différentes applications, car toutes ces applications peuvent stocker ses données dans le même répertoire (ou sous-dossiers), en outre si Lorsque vous désinstallez une application, les données créées par celle-ci existent toujours sur le stockage externe.

Android API Level 29+

Avec Android API 29+, chaque application stocke ses données créées dans un dossier différent sur le stockage externe. Lorsqu'un utilisateur supprime une application, toutes les données créées par celle-ci sont également supprimées.

if (android.os.Build.VERSION.SDK_INT >= 29) {

     // ==> /storage/emulated/0/Android/data/org.o7planning.externalstoragedemo/files
     File dir = this.getExternalFilesDir(null);

}

Utiliser Android Device File Explorer

Cette classe peut vous être utile lorsque vous travaillez avec un stockage externe:

ExternalStorageUtils

package org.o7planning.externalstoragedemo.utils;

import android.content.Context;
import android.os.Build;
import android.os.Environment;
import android.os.StatFs;

import androidx.annotation.RequiresApi;

import java.io.File;

public class ExternalStorageUtils {

    // Check whether the external storage is mounted or not.
    public static boolean isExternalStorageMounted() {

        String dirState = Environment.getExternalStorageState();
        if(Environment.MEDIA_MOUNTED.equals(dirState))
        {
            return true;
        }else
        {
            return false;
        }
    }

    // Check whether the external storage is read only or not.
    public static boolean isExternalStorageReadOnly() {

        String dirState = Environment.getExternalStorageState();
        if(Environment.MEDIA_MOUNTED_READ_ONLY.equals(dirState))
        {
            return true;
        }else
        {
            return false;
        }
    }


    // Get private external storage base directory.
    public static String getPrivateExternalStorageBaseDir(Context context, String dirType)
    {
        String ret = "";
        if(isExternalStorageMounted()) {
            File file = context.getExternalFilesDir(dirType);
            ret = file.getAbsolutePath();
        }
        return ret;
    }

    // Get private cache external storage base directory.
    public static String getPrivateCacheExternalStorageBaseDir(Context context)
    {
        String ret = "";
        if(isExternalStorageMounted()) {
            File file = context.getExternalCacheDir();
            ret = file.getAbsolutePath();
        }
        return ret;
    }


    // Get public external storage base directory.
    public static String getPublicExternalStorageBaseDir()
    {
        String ret = "";
        if(isExternalStorageMounted()) {
            File file = Environment.getExternalStorageDirectory();
            ret = file.getAbsolutePath();
        }
        return ret;
    }

    // Get public external storage base directory.
    public static String getPublicExternalStorageBaseDir(String dirType)
    {
        String ret = "";
        if(isExternalStorageMounted()) {
            File file = Environment.getExternalStoragePublicDirectory(dirType);
            ret = file.getAbsolutePath();
        }
        return ret;
    }

    // Get external storage disk space, return MB
    @RequiresApi(api = Build.VERSION_CODES.JELLY_BEAN_MR2)
    public static long getExternalStorageSpace() {
        long ret = 0;
        if (isExternalStorageMounted()) {
            StatFs fileState = new StatFs(getPublicExternalStorageBaseDir());

            // Get total block count.
            long count = fileState.getBlockCountLong();

            // Get each block size.
            long size = fileState.getBlockSizeLong();

            // Calculate total space size
            ret = count * size / 1024 / 1024;
        }
        return ret;
    }

    // Get external storage left free disk space, return MB
    @RequiresApi(api = Build.VERSION_CODES.JELLY_BEAN_MR2)
    public static long getExternalStorageLeftSpace() {
        long ret = 0;
        if (isExternalStorageMounted()) {
            StatFs fileState = new StatFs(getPublicExternalStorageBaseDir());

            // Get free block count.
            long count = fileState.getFreeBlocksLong();

            // Get each block size.
            long size = fileState.getBlockSizeLong();

            // Calculate free space size
            ret = count * size / 1024 / 1024;
        }
        return ret;
    }

    // Get external storage available disk space, return MB
    @RequiresApi(api = Build.VERSION_CODES.JELLY_BEAN_MR2)
    public static long getExternalStorageAvailableSpace() {
        long ret = 0;
        if (isExternalStorageMounted()) {
            StatFs fileState = new StatFs(getPublicExternalStorageBaseDir());

            // Get available block count.
            long count = fileState.getAvailableBlocksLong();

            // Get each block size.
            long size = fileState.getBlockSizeLong();

            // Calculate available space size
            ret = count * size / 1024 / 1024;
        }
        return ret;
    }
}

2. Par exemple, lire et écrire des fichiers sur un stockage externe

Create a project named ExternalStorageDemo.

File > New > New Project > Empty Activity
- Name: ExternalStorageDemo
- Package name: org.o7planning.externalstoragedemo
- Language: Java

AndroidManifest.xml configuration allows read and write data on the external storage memory.

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

Full content of AndroidManifest.xml:

AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="org.o7planning.externalstoragedemo">

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

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>

The application interface:

Si vous êtes intéressé par les étapes de conception d'interface de cette application, veuillez consulter l'annexe à la fin de l'article.

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout
    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"
    tools:context=".MainActivity">

    <EditText
        android:id="@+id/editText"
        android:layout_width="0dp"
        android:layout_height="48dp"
        android:layout_marginStart="16dp"
        android:layout_marginLeft="16dp"
        android:layout_marginTop="19dp"
        android:layout_marginEnd="16dp"
        android:layout_marginRight="16dp"
        android:ems="10"
        android:inputType="textPersonName"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <LinearLayout
        android:id="@+id/linearLayout"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_marginStart="16dp"
        android:layout_marginLeft="16dp"
        android:layout_marginTop="16dp"
        android:layout_marginEnd="16dp"
        android:layout_marginRight="16dp"
        android:orientation="horizontal"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/editText">

        <Button
            android:id="@+id/button_save"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_weight="0"
            android:text="Save" />

        <Button
            android:id="@+id/button_read"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_weight="0"
            android:text="Read" />

        <Button
            android:id="@+id/button_list"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_weight="0"
            android:text="List Dirs" />
    </LinearLayout>

    <TextView
        android:id="@+id/textView"
        android:layout_width="0dp"
        android:layout_height="0dp"
        android:layout_marginStart="16dp"
        android:layout_marginLeft="16dp"
        android:layout_marginTop="16dp"
        android:layout_marginEnd="16dp"
        android:layout_marginRight="16dp"
        android:layout_marginBottom="16dp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/linearLayout" />
</androidx.constraintlayout.widget.ConstraintLayout>

MainActivity.java

package org.o7planning.externalstoragedemo;

import androidx.appcompat.app.AppCompatActivity;
import androidx.core.app.ActivityCompat;

import android.Manifest;
import android.content.pm.PackageManager;
import android.os.Bundle;
import android.os.Environment;
import android.util.Log;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;

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

public class MainActivity extends AppCompatActivity {
    private EditText editText;
    private TextView textView;
    private Button saveButton;
    private Button readButton;
    private Button listButton;

    private static final String LOG_TAG = "ExternalStorageDemo";


    private static final int REQUEST_ID_READ_PERMISSION = 100;
    private static final int REQUEST_ID_WRITE_PERMISSION = 200;

    private final String fileName = "note.txt";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        editText = (EditText) findViewById(R.id.editText);
        textView = (TextView) findViewById(R.id.textView);

        saveButton = (Button) findViewById(R.id.button_save);
        readButton = (Button) findViewById(R.id.button_read);
        listButton = (Button) findViewById(R.id.button_list);

        saveButton.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View arg0) {
                askPermissionAndWriteFile();
            }

        });

        readButton.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View arg0) {
                askPermissionAndReadFile();
            }

        });

        listButton.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View arg0) {
                listExternalStorages();
            }

        });
    }

    private void askPermissionAndWriteFile() {
        boolean canWrite = this.askPermission(REQUEST_ID_WRITE_PERMISSION,
                Manifest.permission.WRITE_EXTERNAL_STORAGE);
        if(!canWrite)  {
            Toast.makeText(getApplicationContext(),
                    "You do not allow this app to write files.", Toast.LENGTH_LONG).show();
            return;
        }
        //
         this.writeFile();
    }

    private void askPermissionAndReadFile() {
        boolean canRead = this.askPermission(REQUEST_ID_READ_PERMISSION,
                Manifest.permission.READ_EXTERNAL_STORAGE);
        //
        if (!canRead) {
            Toast.makeText(getApplicationContext(),
                    "You do not allow this app to read files.", Toast.LENGTH_LONG).show();
            return;
        }
        //
        this.readFile();
    }

    // With Android Level >= 23, you have to ask the user
    // for permission with device (For example read/write data on the device).
    private boolean askPermission(int requestId, String permissionName) {


        Log.i(LOG_TAG, "Ask for Permission: " + permissionName);
        Log.i(LOG_TAG, "Build.VERSION.SDK_INT: " + android.os.Build.VERSION.SDK_INT);

        if (android.os.Build.VERSION.SDK_INT >= 23) {

            // Check if we have permission
            int permission = ActivityCompat.checkSelfPermission(this, permissionName);

            Log.i(LOG_TAG, "permission: " + permission);
            Log.i(LOG_TAG, "PackageManager.PERMISSION_GRANTED: " + PackageManager.PERMISSION_GRANTED);

            if (permission != PackageManager.PERMISSION_GRANTED) {
                // If don't have permission so prompt the user.
                this.requestPermissions(
                        new String[]{permissionName},
                        requestId
                );
                return false;
            }
        }
        return true;
    }


    // As soon as the user decides, allows or doesn't allow.
    @Override
    public void onRequestPermissionsResult(int requestCode,
                                           String permissions[], int[] grantResults) {

        super.onRequestPermissionsResult(requestCode, permissions, grantResults);
        //
        // Note: If request is cancelled, the result arrays are empty.
        if (grantResults.length > 0) {
            switch (requestCode) {
                case REQUEST_ID_READ_PERMISSION: {
                    if (grantResults[0] == PackageManager.PERMISSION_GRANTED) {
                        readFile();
                    }
                }
                case REQUEST_ID_WRITE_PERMISSION: {
                    if (grantResults[0] == PackageManager.PERMISSION_GRANTED) {
                        writeFile();
                    }
                }
            }
        } else {
            Toast.makeText(getApplicationContext(), "Permission Cancelled!", Toast.LENGTH_SHORT).show();
        }
    }

    // IMPORTANT!!
    public File getAppExternalFilesDir()  {
        if (android.os.Build.VERSION.SDK_INT >= 29) {
            // /storage/emulated/0/Android/data/org.o7planning.externalstoragedemo/files
            return this.getExternalFilesDir(null);
        } else {
            // @Deprecated in API 29.
            // /storage/emulated/0
            return Environment.getExternalStorageDirectory();
        }
    }


    private void writeFile() {
        try {
            File extStore = this.getAppExternalFilesDir( );

            boolean canWrite = extStore.canWrite();
            Log.i(LOG_TAG, "Can write: " + extStore.getAbsolutePath()+" : " + canWrite);

            // ==> /storage/emulated/0/note.txt  (API < 29)
            // ==> /storage/emulated/0/Android/data/org.o7planning.externalstoragedemo/files/note.txt (API >=29)
            String path = extStore.getAbsolutePath() + "/" + fileName;
            Log.i(LOG_TAG, "Save to: " + path);

            String data = editText.getText().toString();
            Log.i(LOG_TAG, "Data: " + data);


            File myFile = new File(path);
            FileOutputStream fOut = new FileOutputStream(myFile);
            fOut.write(data.getBytes("UTF-8"));
            fOut.close();

            Toast.makeText(getApplicationContext(), fileName + " saved", Toast.LENGTH_LONG).show();
        } catch (Exception e) {
            Toast.makeText(getApplicationContext(), "Write Error:" + e.getMessage(), Toast.LENGTH_LONG).show();
            Log.e(LOG_TAG, "Write Error: " + e.getMessage());
            e.printStackTrace();
        }
    }

    private void readFile() {

        File extStore = this.getAppExternalFilesDir();

        // ==> /storage/emulated/0/note.txt  (API < 29)
        // ==> /storage/emulated/0/Android/data/org.o7planning.externalstoragedemo/note.txt (API >=29)
        String path = extStore.getAbsolutePath() + "/" + fileName;
        Log.i(LOG_TAG, "Read file: " + path);

        String s = "";
        String fileContent = "";
        try {
            File myFile = new File(path);
            FileInputStream fIn = new FileInputStream(myFile);
            BufferedReader myReader = new BufferedReader(
                    new InputStreamReader(fIn));

            while ((s = myReader.readLine()) != null) {
                fileContent += s + "\n";
            }
            myReader.close();

            this.textView.setText(fileContent);
        } catch (IOException e) {
            Toast.makeText(getApplicationContext(), "Read Error:" + e.getMessage(), Toast.LENGTH_LONG).show();
            Log.e(LOG_TAG, "Read Error: " + e.getMessage());
            e.printStackTrace();
        }
        Toast.makeText(getApplicationContext(), fileContent, Toast.LENGTH_LONG).show();
    }

    private void listExternalStorages() {
        StringBuilder sb = new StringBuilder();

        sb.append("Data Directory: ").append("\n - ")
                .append(Environment.getDataDirectory().toString()).append("\n");

        sb.append("Download Cache Directory: ").append("\n - ")
                .append(Environment.getDownloadCacheDirectory().toString()).append("\n");

        sb.append("External Storage State: ").append("\n - ")
                .append(Environment.getExternalStorageState().toString()).append("\n");

        sb.append("External Storage Directory: ").append("\n - ")
                .append(Environment.getExternalStorageDirectory().toString()).append("\n");

        sb.append("Is External Storage Emulated?: ").append("\n - ")
                .append(Environment.isExternalStorageEmulated()).append("\n");

        sb.append("Is External Storage Removable?: ").append("\n - ")
                .append(Environment.isExternalStorageRemovable()).append("\n");

        sb.append("External Storage Public Directory (Music): ").append("\n - ")
                .append(Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_MUSIC).toString()).append("\n");

        sb.append("Download Cache Directory: ").append("\n - ")
                .append(Environment.getDownloadCacheDirectory().toString()).append("\n");

        sb.append("Root Directory: ").append("\n - ")
                .append(Environment.getRootDirectory().toString()).append("\n");

        Log.i(LOG_TAG, sb.toString());
        this.textView.setText(sb.toString());
    }

}