在Android中的外部存储中写入文件

Question

我想在外部存储sdCard中创建一个文件并写入它.我已经通过互联网搜索并尝试但没有得到结果,我已经在Android Manifest文件中添加了权限,我在模拟器上这样做,我正在尝试下面的代码和获取ERRR","无法创建文件".

btnWriteSDFile = (Button) findViewById(R.id.btnWriteSDFile);
btnWriteSDFile.setOnClickListener(new OnClickListener() {
    //private Throwable e;

    @Override
    public void onClick(View v) {
        // write on SD card file data from the text box
        try {
            File myFile = new File("/sdcard/mysdfile.txt");
            myFile.createNewFile();
            FileOutputStream fOut = new FileOutputStream(myFile);
            OutputStreamWriter myOutWriter = new OutputStreamWriter(fOut);
            myOutWriter.append(txtData.getText());
            myOutWriter.close();
            fOut.close();

        } catch (Exception e) {
              Log.e("ERRR", "Could not create file",e);
        } 
    }// onClick
}); // btnWriteSDFile

Answer 1

您也可以使用此代码执行此操作.

 public class WriteSDCard extends Activity {

 private static final String TAG = "MEDIA";
 private TextView tv;

  /** Called when the activity is first created. */
@Override
 public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);     
    tv = (TextView) findViewById(R.id.TextView01);
    checkExternalMedia();
    writeToSDFile();
    readRaw();
 }

/** Method to check whether external media available and writable. This is adapted from
   http://developer.android.com/guide/topics/data/data-storage.html#filesExternal */

 private void checkExternalMedia(){
      boolean mExternalStorageAvailable = false;
    boolean mExternalStorageWriteable = false;
    String state = Environment.getExternalStorageState();

    if (Environment.MEDIA_MOUNTED.equals(state)) {
        // Can read and write the media
        mExternalStorageAvailable = mExternalStorageWriteable = true;
    } else if (Environment.MEDIA_MOUNTED_READ_ONLY.equals(state)) {
        // Can only read the media
        mExternalStorageAvailable = true;
        mExternalStorageWriteable = false;
    } else {
        // Can't read or write
        mExternalStorageAvailable = mExternalStorageWriteable = false;
    }   
    tv.append("\n\nExternal Media: readable="
            +mExternalStorageAvailable+" writable="+mExternalStorageWriteable);
}

/** Method to write ascii text characters to file on SD card. Note that you must add a 
   WRITE_EXTERNAL_STORAGE permission to the manifest file or this method will throw
   a FileNotFound Exception because you won't have write permission. */

private void writeToSDFile(){

    // Find the root of the external storage.
    // See http://developer.android.com/guide/topics/data/data-  storage.html#filesExternal

    File root = android.os.Environment.getExternalStorageDirectory(); 
    tv.append("\nExternal file system root: "+root);

    // See http://stackoverflow.com/questions/3551821/android-write-to-sd-card-folder

    File dir = new File (root.getAbsolutePath() + "/download");
    dir.mkdirs();
    File file = new File(dir, "myData.txt");

    try {
        FileOutputStream f = new FileOutputStream(file);
        PrintWriter pw = new PrintWriter(f);
        pw.println("Hi , How are you");
        pw.println("Hello");
        pw.flush();
        pw.close();
        f.close();
    } catch (FileNotFoundException e) {
        e.printStackTrace();
        Log.i(TAG, "******* File not found. Did you" +
                " add a WRITE_EXTERNAL_STORAGE permission to the   manifest?");
    } catch (IOException e) {
        e.printStackTrace();
    }   
    tv.append("\n\nFile written to "+file);
}

/** Method to read in a text file placed in the res/raw directory of the application. The
  method reads in all lines of the file sequentially. */

private void readRaw(){
    tv.append("\nData read from res/raw/textfile.txt:");
    InputStream is = this.getResources().openRawResource(R.raw.textfile);
    InputStreamReader isr = new InputStreamReader(is);
    BufferedReader br = new BufferedReader(isr, 8192);    // 2nd arg is buffer size

    // More efficient (less readable) implementation of above is the composite expression
    /*BufferedReader br = new BufferedReader(new InputStreamReader(
            this.getResources().openRawResource(R.raw.textfile)), 8192);*/

    try {
        String test;    
        while (true){               
            test = br.readLine();   
            // readLine() returns null if no more lines in the file
            if(test == null) break;
            tv.append("\n"+"    "+test);
        }
        isr.close();
        is.close();
        br.close();
    } catch (IOException e) {
        e.printStackTrace();
    }
    tv.append("\n\nThat is all");
}
}

Answer 2

要在Lollipop +设备中写入外部存储,我们需要:

1. 将以下权限添加到Manifest中:

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

2. 请求用户批准:

          public static final int REQUEST_WRITE_STORAGE = 112; 
   
          private requestPermission(Activity context) {
              boolean hasPermission = (ContextCompat.checkSelfPermission(context, Manifest.permission.WRITE_EXTERNAL_STORAGE) == PackageManager.PERMISSION_GRANTED);
              if (!hasPermission) {
                 ActivityCompat.requestPermissions(context,
                    new String[]{Manifest.permission.WRITE_EXTERNAL_STORAGE},
                  REQUEST_WRITE_STORAGE);
              } else {
                // You are allowed to write external storage:
                String path = Environment.getExternalStorageDirectory().getAbsolutePath() + "/new_folder";
                File storageDir = new File(path);
                if (!storageDir.exists() && !storageDir.mkdirs()) {
                  // This should never happen - log handled exception!
                }
              }
   

3. 处理Activity内的用户响应:

   @Override
   public void onRequestPermissionsResult(int requestCode, String[] permissions, int[] grantResults) {
        super.onRequestPermissionsResult(requestCode, permissions, grantResults);
   
        switch (requestCode)
        {
         case Preferences.REQUEST_WRITE_STORAGE: {
            if (grantResults.length > 0 && grantResults[0] ==  PackageManager.PERMISSION_GRANTED) {
              Toast.makeText(this, "The app was allowed to write to your storage!", Toast.LENGTH_LONG).show();
              // Reload the activity with permission granted or use the features what required the permission
            } else {
              Toast.makeText(this, "The app was not allowed to write to your storage. Hence, it cannot function properly. Please consider granting it this permission", Toast.LENGTH_LONG).show();
           }
        }
    }