Android写bitmap对象到文件中

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关于Android file.createNewFile() 方法出现的问题总结

http://my.oschina.net/AlexZhuang/blog/55764

今天在编写向SDcard中，创建文件夹并向其中保存文件的过程中出现个一系列的问题在此做下总结：

1.首先要注意权限问题

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

01String local_file = Environment.getExternalStorageDirectory().getAbsolutePath()+"/down/";
02  
03File f =new File(local_file);
04  
05if(!f.exists()){
06  
07f.mkdirs();
08  
09}
10  
11String local_file = f.getAbsolutePath()+"/"+filename;
12  
13File f =new File(local_file);
14  
15try{ 
16  
17   if(!file.createNewFile()) {
18  
19       System.out.println("File already exists");
20  
21   } 
22  
23}catch (IOException ex) {
24  
25   System.out.println(ex);
26  
27}

2.file.createNewFile() 方法出现的问题

会出现No such file ..的问题

需要注意的是：要先对设计的文件路径创建文件夹，然后在对文件进行创建

@Override
public void onClick(View v) {
  // TODO Auto-generated method stub
  File f = new File(path);
  f.exists();
  if (v.getId() == R.id.btn) {

   try {
    fd = ParcelFileDescriptor.open(f, ParcelFileDescriptor.MODE_READ_ONLY);

    bm = BitmapFactory.decodeFileDescriptor(fd.getFileDescriptor(),null, null);

    File temp = new File("/mnt/sdcard/mtk/lock.png");

    if (!temp.exists()) {
     try {
      temp.createNewFile();
     } catch (IOException e) {
      // TODO Auto-generated catch block
      e.printStackTrace();
     }
    }
    outputStream = new FileOutputStream("/mnt/sdcard/mtk/lock.png");

    if (outputStream != null) {
     dumpBitmap(bm, outputStream);
             }

   } catch (FileNotFoundException e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
   }
  }

  if (v.getId() == R.id.btn02) {
   try {
    fd = ParcelFileDescriptor.open(f, ParcelFileDescriptor.MODE_READ_ONLY);

    bm = BitmapFactory.decodeFileDescriptor(fd.getFileDescriptor(),null, null);

    File temp = new File("/mnt/sdcard/mtk/wall.png");

    if (!temp.exists()) {
     try {
      temp.createNewFile();
     } catch (IOException e) {
      // TODO Auto-generated catch block
      e.printStackTrace();
     }
    }

    outputStream = new FileOutputStream("/mnt/sdcard/mtk/wall.png");

    if (outputStream != null) {
     dumpBitmap(bm, outputStream);
             }

   } catch (FileNotFoundException e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
   }
  }
}

private void dumpBitmap(Bitmap bm, OutputStream outputStream2) {
  // TODO Auto-generated method stub
  bm.compress(Bitmap.CompressFormat.PNG, 100, outputStream2);
}

private static void dumpBitmap(Bitmap b) {
     if (b != null) {
         java.io.FileOutputStream fos = null;
         try {
             String filename = android.os.Environment.getExternalStorageDirectory().toString()+"/DCIM/Bitmap["+
                      android.os.SystemClock.uptimeMillis() + "].png";
             fos = new java.io.FileOutputStream(filename);
             b.compress(Bitmap.CompressFormat.PNG, 100, fos);
         } catch (java.io.IOException ex) {
             // MINI_THUMBNAIL not exists, ignore the exception and generate one.
         } finally {
             if (fos != null) {
             try {
                 fos.close();
             } catch (java.io.IOException ex) {
             }
             }
         }
     }
}