使用getExternalStoragePublicDirectory会损坏安卓文件

Question

当我想通过我的应用程序将图片保存到Android时，我遇到了这个奇怪的问题。图像被损坏了，现在Android不能使用它们。我看不出我的代码有什么问题。

以下是我的下载方法：

    public void createExternalStoragePublicPicture(String DownloadUrl, String fileName) {
    // Create a path where we will place our picture in the user's
    // public pictures directory.  Note that you should be careful about
    // what you place here, since the user often manages these files.  For
    // pictures and other media owned by the application, consider
    // Context.getExternalMediaDir().

    Log.i("Download", DownloadUrl);
    Log.i("File", fileName);

    File path = Environment.getExternalStoragePublicDirectory(
            Environment.DIRECTORY_PICTURES);
    File file = new File(path, fileName);

    try {
        // Make sure the Pictures directory exists.
        path.mkdirs();

        // Very simple code to copy a picture from the application's
        // resource into the external file.  Note that this code does
        // no error checking, and assumes the picture is small (does not
        // try to copy it in chunks).  Note that if external storage is
        // not currently mounted this will silently fail.
        URL url = new URL(DownloadUrl);
        URLConnection ucon = url.openConnection();

        InputStream is = ucon.getInputStream();
        OutputStream os = new FileOutputStream(file);
        byte[] data = new byte[is.available()];
        is.read(data);
        os.write(data);
        is.close();
        os.close();

        // Tell the media scanner about the new file so that it is
        // immediately available to the user.
        MediaScannerConnection.scanFile(this,
                new String[] { file.toString() }, null,
                new MediaScannerConnection.OnScanCompletedListener() {
            public void onScanCompleted(String path, Uri uri) {
                Log.i("ExternalStorage", "Scanned " + path + ":");
                Log.i("ExternalStorage", "-> uri=" + uri);
            }
        });
    } catch (IOException e) {
        // Unable to create file, likely because external storage is
        // not currently mounted.
        Log.w("ExternalStorage", "Error writing " + file, e);
    }
}

你知道这里出了什么问题吗？

Answer 1

is.available()可能不会像您期望的那样工作。通常，您不应该依赖available()，因为它没有严格指定它返回的值。

参见InputStream：“特别重要的是要认识到，您不能使用此方法来调整容器的大小，并假定您可以读取整个流...")

使用常见的“循环”-approach：

int c;
while ( (c = is.read(buf)) >= 0 ) {
  os.write(buf,0,c)
}

这样可以确保您真正读取了源文件中的所有字节。