Android - 009 - File access ( READ / WRITE )

android.009.java

//////////////////////////////////////////////////////////////////////////////////////////////
// AndroidManifest.xml
//////////////////////////////////////////////////////////////////////////////////////////////

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="....">
    
    // WRITE_EXTERNAL_STORAGE permission is enough for both reading and writing
    <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/>
    // WRITE_EXTERNAL_STORAGE permission is enough for both reading and writing
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>

    <application
    ......
    </application>
</manifest>

//////////////////////////////////////////////////////////////////////////////////////////////
// MainActivity
//////////////////////////////////////////////////////////////////////////////////////////////

public class MainActivity extends AppCompatActivity {

    private void auslesen() {
        try {
            String dateiname = Environment.getExternalStorageDirectory() + "/Dateien/android.txt";
            FileReader fr = new FileReader(dateiname);
            BufferedReader br = new BufferedReader(fr);
            String zeile;
            
            zeile = br.readLine();
            
            // 
            while (zeile != null) {
                // do sth with the zeile, eg lbl.append(zeile + "\n");
                zeile = br.readLine();
            }

            br.close();
            fr.close();

        } catch (Exception ex) {
            lbl.append("\n\n" + ex.getMessage());
        }

    }

    // Beim Beebden der App soll die aktuelle Uhrzeit in die Datei geschrieben werden
    // Beim nächsten Start der App wird die Info wiedergelesen und angezeigt
    @Override
    protected void onDestroy() {

        try {
            String dateiname = Environment.getExternalStorageDirectory() + "/Dateien/android.txt";
            SimpleDateFormat sdf = new SimpleDateFormat("HH:mm:ss");

            File file = new File(dateiname);
            FileWriter fw = new FileWriter(file);
            fw.append(sdf.format(new Date())+"\n");
            fw.close();

        } catch (Exception ex) {
            lbl.append("\n\n" + ex.getMessage());
        }

        super.onDestroy();
    }

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        ...............

        // Abfragen ob Permission geteilt wurde NUR wenn sie tatsächlich
        // noch nicht erteilt wurde
        if(ActivityCompat.checkSelfPermission(this
                , Manifest.permission.WRITE_EXTERNAL_STORAGE) !=PackageManager.PERMISSION_GRANTED) {

            // abzufragende Berechtigungen in ein Array stecken
            String[] permissions = {Manifest.permission.READ_EXTERNAL_STORAGE, Manifest.permission.WRITE_EXTERNAL_STORAGE};

            // ... und Abfrage starten
            requestPermissions(permissions, 1);
        }

        if(ActivityCompat.checkSelfPermission(this
                , Manifest.permission.READ_EXTERNAL_STORAGE) ==PackageManager.PERMISSION_GRANTED)
            auslesen();
    }
}