即使給定了讀/寫權限，也無法從外部存儲讀取或創建文件

Question

這是清單文件：

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

...

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

    <application
        android:requestLegacyExternalStorage="true"
        android:allowBackup="true"

...

</manifest>

我使用了 tedpermission。 用於 i/o 操作的外部存儲（例如：storage/emulated/0/myDiary/2020_10_23.txt）中按日期（例如：2020_10_23.txt）命名的文本文件。

這里主要活動的核心代碼：

 PermissionListener permissionlistener = new PermissionListener() {
        @Override
        public void onPermissionGranted() {
            Toast.makeText(MainActivity.this, "Permission granted", Toast.LENGTH_SHORT).show();
        }

        @Override
        public void onPermissionDenied(List<String> deniedPermissions) {
            Toast.makeText(MainActivity.this, "Permission denied\n" + deniedPermissions.toString(), Toast.LENGTH_SHORT).show();
        }
    };

    @RequiresApi(api = Build.VERSION_CODES.R)
    @Override
    public void onCreate(Bundle savedInstanceState) {
        TedPermission.with(this)
                .setPermissionListener(permissionlistener)
                .setDeniedMessage("External Storage READ/WRITE Denied")
                .setPermissions(Manifest.permission.WRITE_EXTERNAL_STORAGE, Manifest.permission.READ_EXTERNAL_STORAGE)
                .check();

...

   final String sdPath = Environment.getExternalStorageDirectory().getAbsolutePath();
   final File myDir = new File(sdPath + "/myDiary");
   string fileName = Integer.toString(year) + "_"
                        + Integer.toString(monthOfYear + 1) + "_"
                        + Integer.toString(dayOfMonth) + ".txt";

...

 btnWrite.setOnClickListener(new View.OnClickListener() {
            @RequiresApi(api = Build.VERSION_CODES.O)
            public void onClick(View v) {
                try {
                    //openFileoutput Methods does not allow path delimiters.                    
                    File current_file = new File(myDir + "/" + fileName);

                    if (!current_file.getParentFile().exists()) {
                        if (!current_file.getParentFile().mkdirs()) {
                            Toast.makeText(getApplicationContext(),
                                    "Failed to create folder : " + myDir, Toast.LENGTH_SHORT).show();
                        }
                    }

                    if (!current_file.exists()) {
                        if (!current_file.createNewFile()) {
                            Toast.makeText(getApplicationContext(),
                                    "Failed to create file : " + myDir + "/" + fileName, Toast.LENGTH_SHORT).show();
                        }
                    }

                    FileOutputStream outFs = new FileOutputStream(new File(String.valueOf(current_file)));

                    String str = edtDiary.getText().toString();
                    outFs.write(str.getBytes());
                    outFs.close();

                    Toast.makeText(getApplicationContext(),
                            fileName + " is saved", Toast.LENGTH_SHORT).show();

                } catch (IOException e) {
                    Toast.makeText(getApplicationContext(),
                            "Failed to save file : " + myDir + "/" + fileName, Toast.LENGTH_SHORT).show();
                    e.printStackTrace();
                }

            }
        });

...
//read text file from external storage
String readDiary(String fName) {
        String diaryStr = null;
        FileInputStream inFs;
        try {
            inFs = new FileInputStream(new File(fName));
            byte[] txt = new byte[500];
            inFs.read(txt);
            inFs.close();
            diaryStr = (new String(txt)).trim();
            btnWrite.setText("modify");
        } catch (IOException e) {
            edtDiary.setHint("no existing diary");
            btnWrite.setText("new save");
        }
        return diaryStr;
    }

安卓版本：11

應用權限 ：

這是 logcat：

2020-10-23 15:40:00.986 6178-6178/com.cookandroid.project8_1 W/System.err: java.io.IOException: No such file or directory
2020-10-23 15:40:00.986 6178-6178/com.cookandroid.project8_1 W/System.err:     at java.io.UnixFileSystem.createFileExclusively0(Native Method)
2020-10-23 15:40:00.986 6178-6178/com.cookandroid.project8_1 W/System.err:     at java.io.UnixFileSystem.createFileExclusively(UnixFileSystem.java:317)
2020-10-23 15:40:00.986 6178-6178/com.cookandroid.project8_1 W/System.err:     at java.io.File.createNewFile(File.java:1008)
2020-10-23 15:40:00.986 6178-6178/com.cookandroid.project8_1 W/System.err:     at com.cookandroid.project8_1.MainActivity$3.onClick(MainActivity.java:102)
2020-10-23 15:40:00.987 6178-6178/com.cookandroid.project8_1 W/System.err:     at android.view.View.performClick(View.java:7448)
2020-10-23 15:40:00.987 6178-6178/com.cookandroid.project8_1 W/System.err:     at android.view.View.performClickInternal(View.java:7425)
2020-10-23 15:40:00.987 6178-6178/com.cookandroid.project8_1 W/System.err:     at android.view.View.access$3600(View.java:810)
2020-10-23 15:40:00.987 6178-6178/com.cookandroid.project8_1 W/System.err:     at android.view.View$PerformClick.run(View.java:28305)
2020-10-23 15:40:00.987 6178-6178/com.cookandroid.project8_1 W/System.err:     at android.os.Handler.handleCallback(Handler.java:938)
2020-10-23 15:40:00.987 6178-6178/com.cookandroid.project8_1 W/System.err:     at android.os.Handler.dispatchMessage(Handler.java:99)
2020-10-23 15:40:00.987 6178-6178/com.cookandroid.project8_1 W/System.err:     at android.os.Looper.loop(Looper.java:223)
2020-10-23 15:40:00.987 6178-6178/com.cookandroid.project8_1 W/System.err:     at android.app.ActivityThread.main(ActivityThread.java:7656)
2020-10-23 15:40:00.987 6178-6178/com.cookandroid.project8_1 W/System.err:     at java.lang.reflect.Method.invoke(Native Method)
2020-10-23 15:40:00.987 6178-6178/com.cookandroid.project8_1 W/System.err:     at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:592)
2020-10-23 15:40:00.987 6178-6178/com.cookandroid.project8_1 W/System.err:     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:947)

它無法在 storage/emulated/0 上創建文件夾 'myDiary'我嘗試了所有我能做的。 為什么即使我給了外部存儲 I/O 權限也無法創建文件夾、文件？

Answer 1

用這個

public class Folder
{
    private final File appDataFolder;

    public Folder()
    {
        File file = Environment.getExternalStorageDirectory();

        appDataFolder = new File(file, "AppDataFolder");

        if (!appDataFolder.exists()) appDataFolder.mkdir();
    }

    public String getMainFolder()
    {
        return appDataFolder.getAbsolutePath();
    }

    public void deleteMainFolder()
    {
        if (appDataFolder.isDirectory())
        {
            String[] children = appDataFolder.list();

            for (String child : children)
            {
                new File(appDataFolder, child).delete();
            }
        }

        new Folder();
    }

    public void createNewFolder(String folderName)
    {
        File file = new File(appDataFolder, folderName);

        if (!file.exists()) file.mkdir();
    }

    public void createChildFolder(String parentName, String childName)
    {
        String path = appDataFolder.getAbsolutePath() + File.separator + parentName;

        File parent = new File(path);

        File file = new File(parent, childName);

        if (!file.exists()) file.mkdir();
    }
}

並在活動中

PermissionListener permissionlistener = new PermissionListener() {
        @Override
        public void onPermissionGranted() {
            new Folder().createNewFolder("myDiary");
            Toast.makeText(MainActivity.this, "Permission granted", Toast.LENGTH_SHORT).show();
        }

        @Override
        public void onPermissionDenied(List<String> deniedPermissions) {
            Toast.makeText(MainActivity.this, "Permission denied\n" + deniedPermissions.toString(), Toast.LENGTH_SHORT).show();
        }
    };

Answer 2

在 Android 11 上，您無權訪問外部存儲的根目錄。

您不能在 /storage/emulated/0 中創建文件或文件夾。

但是..您可以寫入 /storage/emulated/0 上的常用公用文件夾，例如

Download, Documents, DCIM, Pictures, Alarms, a.s.o.

查看您的設備上已有哪些文件夾，您可以將它們主要用於讀取和/或寫入操作。