如何在 Android 10 的外部存储（SD 卡）中创建文件？

Question

I try to make 'File Control' app.

I found how to read file, but I can't find how to write file.

I set permission like this.

AndroidManifast.xml

    <application
    ...
    android:requestLegacyExternalStorage="true"
    ...
    </application>
    <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE"/>
    <uses-permission android:name="android.permission.INTERNET"/>
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
    <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/>

and i call this code in MainActivity.onCreate.

    private static final int REQUEST_EXTERNAL_STORAGE = 1;
    private static String[] PERMISSIONS_STORAGE = {
            Manifest.permission.READ_EXTERNAL_STORAGE,
            Manifest.permission.WRITE_EXTERNAL_STORAGE
    };


    public static void verifyStoragePermissions(Activity activity) {
        // Check if we have write permission
        int permission = ActivityCompat.checkSelfPermission(activity, Manifest.permission.WRITE_EXTERNAL_STORAGE);

        if (permission != PackageManager.PERMISSION_GRANTED) {
            // We don't have permission so prompt the user
            ActivityCompat.requestPermissions(
                    activity,
                    PERMISSIONS_STORAGE,
                    REQUEST_EXTERNAL_STORAGE
            );
        }
    }


    ActivityCompat.requestPermissions(this, new String[]{Manifest.permission.WRITE_EXTERNAL_STORAGE}, MODE_PRIVATE);
    verifyStoragePermissions(this);

I want read and write file, at /storage/3066-3133/title.txt . /storage/3066-3133 is my sdcard path.

read file is work perfectly.

    public void readFile() {

        String fileTitle = "title.txt";
        File file = new File("/storage/3066-3133", fileTitle);

        try {
            BufferedReader reader = new BufferedReader(new FileReader(file));
            String result = "";
            String line;
            while ((line = reader.readLine()) != null) {
                result += line;
            }
            popupToast("read : " + result);

            reader.close();
        } catch (FileNotFoundException e1) {
            e1.printStackTrace();
            popupToast("no file found");

        } catch (IOException e2) {
            e2.printStackTrace();
            popupToast("read fail");
        }

    }

but write code occur exception. write Exception: /storage/3066-3133/title.txt: open failed: EACCES (Permission denied)

    public void writeFile() {
        String fileTitle = "title.txt";
        File file = new File("/storage/3066-3133", fileTitle);

        try {
            if (!file.exists()) {
                file.createNewFile(); // error!!!!
            }
            FileWriter writer = new FileWriter(file, false);
            String str = "      write text     ";
            writer.write(str);
            writer.close();
        } catch (IOException e) {
            e.printStackTrace();
            popupToast("write fail");
        }
    }

Plus, I can write file at /storage/emulated/0/title.txt . /storage/emulated/0 is bullt-in external storage path.

I need more permission for sdcard?

or this is problem? First, i create project for target sdk:31. and i change 29 in build.gradle. changing target sdk is not work? Someone tell sdk 30 little changed. but, if this is problem, i can't understand then why 'read' work...

Answer 1

USE

uses-permission android:name="android.permission.MANAGE_EXTERNAL_STORAGE" in your manifest along with

android:requestLegacyExternalStorage="true" in your < application />