Permission to write on SD card android

问题:

I have a problem writing to the SD card, here is the code: (Sorry about the layout of the code, just copy pased it )

public class SaveAndReadManager {

 private String result;
 private String saveFileName = "eventlist_savefile";

 public String writeToFile( ArrayList<Event> arrlEvents ){
  FileOutputStream fos = null;
  ObjectOutputStream out = null;

  try{
   File root = Environment.getExternalStorageDirectory();

   if( root.canWrite() ){
    fos = new FileOutputStream( saveFileName );
    out = new ObjectOutputStream( fos );
    out.writeObject( arrlEvents );

    result = "File written";

    out.close();
   }else{
    result = "file cant write";
   }
  }catch( IOException e ){
   e.printStackTrace();
   result = "file not written";
  }

  return result;
 }

 public boolean readFromFile(){
  return false;
 }
}

I have not implemented the readFromFile() yet. The problem is that root.canWrite() returns false all the time. Here is the manifest file:

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

<application android:icon="@drawable/icon" android:label="@string/app_name">
    <activity android:name=".InfoScreen"
           android:label="@string/app_name">
      <intent-filter>
            <action android:name="android.intent.action.MAIN" />
            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>

    <activity android:name=".EventCalendar"
              android:label="@string/app_name" />

    <activity android:name=".MakeEvent"
              android:label="@string/app_name" />

    <activity android:name=".ViewEvent"
              android:label="@string/app_name" />

</application>
<uses-sdk android:minSdkVersion="8" />

I've asked for the permission to write, and on my avd, if i go to settings -> SD card and phone storage, it tells me i have 1 gb on the sd card to write on. Please help.

Thanks:)

回答1:

Which result are you seeing retunred from writeToFile? "file not written" or "file cant write"?

When I ran your code it dropped into the catch IOException block with the result of "file not written". The reason for this was that fos was defined incorrectly:

fos = new FileOutputStream( saveFileName );

should be:

fos = new FileOutputStream( root + "/" saveFileName );

After I changed this line, I got the result "File written" returned from writeToFile.

回答2:

Try checking the state of the SD card before you attempt to write to it. It may be used as a shared drive, corrupted, full, etc. A list of states can be found here: http://developer.android.com/reference/android/os/Environment.html

Here's an example of getting the states:

String state = Environment.getExternalStorageState();
    if (Environment.MEDIA_MOUNTED.equals(state)) {
        mExternalStorageAvailable = mExternalStorageWriteable = true;
    } else if (Environment.MEDIA_MOUNTED_READ_ONLY.equals(state)) {
        mExternalStorageAvailable = true;
        mExternalStorageWriteable = false;
    } else {
        mExternalStorageAvailable = mExternalStorageWriteable = false;
    }

回答3:

I use the following code to record audio data (successfully) to my Android's SD Card. My application requires the RECORD_AUDIO permission, but nothing else.

File file = new File (Environment.getExternalStorageDirectory().getAbsolutePath() + FILE_NAME);

if (file.exists())
    file.delete();                                                          //  Delete any previous recording

try
{
    file.createNewFile();                                                   //  Create the new file
}
catch (IOException e)
{
    Log.e (TAG, "Failed to create " + file.toString());
}

try
{
    OutputStream            os  = new FileOutputStream      (file);
    BufferedOutputStream    bos = new BufferedOutputStream  (os, 8000);
    DataOutputStream        dos = new DataOutputStream      (bos);          //  Create a DataOutputStream to write the audio data to the file

    // Create an AudioRecord object to record the audio
    int          bufferSize     = AudioRecord.getMinBufferSize (frequency, channelConfig, Encoding);
    AudioRecord  audioRecord    = new AudioRecord (MediaRecorder.AudioSource.MIC, frequency, channelConfig, Encoding, bufferSize);

    short[] buffer = new short[bufferSize];                                 //  Using "short", because we're using "ENCODING_PCM_16BIT"    
    audioRecord.startRecording();

    while (isRecording)
    {
        int bufferReadResult = audioRecord.read (buffer, 0, bufferSize);
        for (int i = 0; i < bufferReadResult; i++)
            dos.writeShort (buffer[i]);
    }

    audioRecord.stop();
    dos.close();
}
catch (Exception t)
{
    Log.e (TAG, "Recording Failed");
}

It would appear to me that you're missing the getAbsolutePath() call appended to your getExternalStorageDirectory() call (which may have the same result as Marc Bernstein's hard coded solution).

回答4:

I should have included the following link as well (since it's where I got the code that writes to the SD Card...):

http://emeadev.blogspot.com/2009/09/raw-audio-manipulation-in-android.html