Jak utworzyć plik na Androida?

Question

Jak utworzyć plik, zapisać w nim dane i odczytać z niego dane na urządzeniu z systemem Android? Jeśli to możliwe, podaj fragment kodu.

Answer 1

From here: http://www.anddev.org/working_with_files-t115.html

//Writing a file... 



try { 
     // catches IOException below 
     final String TESTSTRING = new String("Hello Android"); 

     /* We have to use the openFileOutput()-method 
     * the ActivityContext provides, to 
     * protect your file from others and 
     * This is done for security-reasons. 
     * We chose MODE_WORLD_READABLE, because 
     * we have nothing to hide in our file */    
     FileOutputStream fOut = openFileOutput("samplefile.txt", 
                  MODE_PRIVATE); 
     OutputStreamWriter osw = new OutputStreamWriter(fOut); 

     // Write the string to the file 
     osw.write(TESTSTRING); 

     /* ensure that everything is 
     * really written out and close */ 
     osw.flush(); 
     osw.close(); 

//Reading the file back... 

     /* We have to use the openFileInput()-method 
     * the ActivityContext provides. 
     * Again for security reasons with 
     * openFileInput(...) */ 

     FileInputStream fIn = openFileInput("samplefile.txt"); 
     InputStreamReader isr = new InputStreamReader(fIn); 

     /* Prepare a char-Array that will 
     * hold the chars we read back in. */ 
     char[] inputBuffer = new char[TESTSTRING.length()]; 

     // Fill the Buffer with data from the file 
     isr.read(inputBuffer); 

     // Transform the chars to a String 
     String readString = new String(inputBuffer); 

     // Check if we read back the same chars that we had written out 
     boolean isTheSame = TESTSTRING.equals(readString); 

     Log.i("File Reading stuff", "success = " + isTheSame); 

    } catch (IOException ioe) 
     {ioe.printStackTrace();} 

Answer 2

Użyłem następujący kod utworzyć plik tymczasowy do pisania bajtów. I działa dobrze.

File file = new File(Environment.getExternalStorageDirectory() + File.separator + "test.txt"); 
file.createNewFile(); 
byte[] data1={1,1,0,0}; 
//write the bytes in file 
if(file.exists()) 
{ 
    OutputStream fo = new FileOutputStream(file);    
    fo.write(data1); 
    fo.close(); 
    System.out.println("file created: "+file); 
    url = upload.upload(file); 
}    

//deleting the file    
file.delete(); 
System.out.println("file deleted"); 

Answer 3

Postanowiłem napisać klasę z tego wątku, która może być pomocna dla innych. Zauważ, że jest to obecnie przeznaczone do zapisu tylko w katalogu "files" (np. Nie zapisuje do ścieżek "sdcard").

import java.io.BufferedReader; 
import java.io.FileInputStream; 
import java.io.FileOutputStream; 
import java.io.IOException; 
import java.io.InputStreamReader; 
import java.io.OutputStreamWriter; 

import android.content.Context; 

public class AndroidFileFunctions { 

    public static String getFileValue(String fileName, Context context) { 
     try { 
      StringBuffer outStringBuf = new StringBuffer(); 
      String inputLine = ""; 
      /* 
      * We have to use the openFileInput()-method the ActivityContext 
      * provides. Again for security reasons with openFileInput(...) 
      */ 
      FileInputStream fIn = context.openFileInput(fileName); 
      InputStreamReader isr = new InputStreamReader(fIn); 
      BufferedReader inBuff = new BufferedReader(isr); 
      while ((inputLine = inBuff.readLine()) != null) { 
       outStringBuf.append(inputLine); 
       outStringBuf.append("\n"); 
      } 
      inBuff.close(); 
      return outStringBuf.toString(); 
     } catch (IOException e) { 
      return null; 
     } 
    } 

    public static boolean appendFileValue(String fileName, String value, 
      Context context) { 
     return writeToFile(fileName, value, context, Context.MODE_APPEND); 
    } 

    public static boolean setFileValue(String fileName, String value, 
      Context context) { 
     return writeToFile(fileName, value, context, 
       Context.MODE_WORLD_READABLE); 
    } 

    public static boolean writeToFile(String fileName, String value, 
      Context context, int writeOrAppendMode) { 
     // just make sure it's one of the modes we support 
     if (writeOrAppendMode != Context.MODE_WORLD_READABLE 
       && writeOrAppendMode != Context.MODE_WORLD_WRITEABLE 
       && writeOrAppendMode != Context.MODE_APPEND) { 
      return false; 
     } 
     try { 
      /* 
      * We have to use the openFileOutput()-method the ActivityContext 
      * provides, to protect your file from others and This is done for 
      * security-reasons. We chose MODE_WORLD_READABLE, because we have 
      * nothing to hide in our file 
      */ 
      FileOutputStream fOut = context.openFileOutput(fileName, 
        writeOrAppendMode); 
      OutputStreamWriter osw = new OutputStreamWriter(fOut); 
      // Write the string to the file 
      osw.write(value); 
      // save and close 
      osw.flush(); 
      osw.close(); 
     } catch (IOException e) { 
      return false; 
     } 
     return true; 
    } 

    public static void deleteFile(String fileName, Context context) { 
     context.deleteFile(fileName); 
    } 
} 

Answer 4

Zapis do pliku Test.txt:

String filepath ="/mnt/sdcard/test.txt"; 
FileOutputStream fos = null; 
try { 
     fos = new FileOutputStream(filepath); 
     byte[] buffer = "This will be writtent in test.txt".getBytes(); 
     fos.write(buffer, 0, buffer.length); 
     fos.close(); 
    } catch (FileNotFoundException e) { 
     e.printStackTrace(); 
    } catch (IOException e) { 
     e.printStackTrace(); 
    }finally{ 
     if(fos != null) 
      fos.close(); 
    } 

Odczyt z pliku Test.txt:

String filepath ="/mnt/sdcard/test.txt";   
FileInputStream fis = null; 
try { 
     fis = new FileInputStream(filepath); 
     int length = (int) new File(filepath).length(); 
     byte[] buffer = new byte[length]; 
     fis.read(buffer, 0, length); 
     fis.close(); 
    } catch (FileNotFoundException e) { 
     e.printStackTrace(); 
    } catch (IOException e) { 
     e.printStackTrace(); 
    }finally{ 
     if(fis != null) 
      fis.close(); 
    } 

Uwaga: nie zapomnij dodać te dwa uprawnienia w AndroidManifest. xml

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