Android SD卡写不起作用

Question

所以我已经查找了几种在Android中写入SD卡的方法，但似乎没有一种方法可以实际写入。我已经在清单中设置了权限。我写的我的FileIO类：

import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStreamWriter;
import java.io.PrintStream;

//import android.app.Activity;
//import android.os.Bundle;
import android.os.Environment;
import android.util.Log;

public class FileIO {

    private static final String TAG = "FileIO";
    private String filename;
    private File sdCard;
    private File dir;

    public FileIO(String path, String filename){
        Log.d(TAG, "Creating new File IO");
        this.filename = filename;
        boolean mExternalStorageAvailable = false;
        boolean mExternalStorageWriteable = false;
        String state = Environment.getExternalStorageState();

        if (Environment.MEDIA_MOUNTED.equals(state)) {
            // We can read and write the media
            Log.d(TAG, "Read and Write OK");
        } else if (Environment.MEDIA_MOUNTED_READ_ONLY.equals(state)) {
            // We can only read the media
            Log.w(TAG, "Read only OK");
        } else {
            // Something else is wrong. It may be one of many other states, but all we need
            //  to know is we can neither read nor write
            Log.w(TAG, "Read and Write BLOCKED");
        }
        sdCard = Environment.getExternalStorageDirectory();
        Log.d(TAG, "Writing to file: " + sdCard.getAbsolutePath()+path);
        dir = new File (sdCard.getAbsolutePath()+path);
        if (dir.mkdirs() || dir.isDirectory()) {
            Log.d(TAG, "SUCCESS - Created directory");
        } else {
            Log.d(TAG, "FAILED - Create directory");
        }

    }

public void writeToFile(String s){
    File file = new File(dir,this.filename);
    try {
        FileOutputStream f = new FileOutputStream(file,true); //True = Append to file, false = Overwrite
        OutputStreamWriter osw = new OutputStreamWriter(f);
        osw.write(s);
        osw.flush();
        f.close();
    } catch (FileNotFoundException e) {
        e.printStackTrace();
        System.out.printf("\nFile not found. Make sure to add WRITE_EXTERNAL_STORAGE permission to the manifest");
    } catch (IOException e) {
        e.printStackTrace();
    }   
}
}

然后这是它正在使用的类。

import android.app.Activity;
import android.text.format.DateFormat;
import android.widget.TextView;

public class AudioClipLogWrapper implements AudioClipListener
{
    private TextView log;

    private Activity context;

    private double previousFrequency = -1;
    private int previousVolume = -1;
    private int previousMax = -1;

    private FileIO fileIO;

    public AudioClipLogWrapper(TextView log, Activity context)
    {
        this.log = log;
        this.context = context;
        String dateStamp = (DateFormat.format("dd-MM-yyyy-hh-mm-ss", new java.util.Date()).toString());
        fileIO = new FileIO("/Android/data/com.uni.Lab7/files/",String.format("audio-%s.txt",dateStamp));

    }

    @Override
    public boolean heard(short[] audioData, int sampleRate)
    {

        final double freq = ZeroCrossing.calculate(sampleRate, audioData);      
        final int maxAmplitude = AudioUtil.getMaxValue(audioData);
        final double volume = AudioUtil.rootMeanSquared(audioData);


        final StringBuilder message = new StringBuilder();
        if ((((int)volume) > (4 * previousVolume)) && (maxAmplitude > (4 * previousMax)) ) {
            message.append(" Clap!");
        }
        previousVolume = (int) volume;
        previousMax= (int) maxAmplitude;

        fileIO.writeToFile(String.format("%d, %d, %f\n",(int)volume, maxAmplitude, freq));

        context.runOnUiThread(new Runnable()
        {
            @Override
            public void run()
            {
               AudioTaskUtil.appendToStartOfLog(log, message.toString());
             }
        });

        return false;
    }
}

当我查看日志时，它表明一切都应该有效：

01-12 23:21:55.815    2752-2752/com.uni.Lab7 D/FileIO﹕ Creating new File IO
01-12 23:21:55.825    2752-2752/com.uni.Lab7 D/FileIO﹕ Read and Write OK
01-12 23:21:55.825    2752-2752/com.uni.Lab7 D/FileIO﹕ Writing to file: /storage/sdcard0/Android/data/com.uni.Lab7/files/
01-12 23:21:55.835    2752-2752/com.uni.Lab7 D/FileIO﹕ SUCCESS - Created directory

但是当我从手机中取出SD卡时，我在电脑上看到没有文件夹也没有文件。我查看了Android write to sd card folder和Write a file in SDcard in Android，我得到了他们的建议。

手机是运行4.1.2的三星GT-S53110B。因此，在我的gradle和manifest中，我将SDK的最小值设为8，目标为16。