Android-如何从SD卡获取文件字节

如何解决Android-如何从SD卡获取文件字节

我正在尝试在sdcard中获取文档的一个字节。我的工作正好是以下内容；

1-）我选择文件。

   fun openFile() {
    val intent = Intent(Intent.ACTION_OPEN_DOCUMENT).apply {
        addCategory(Intent.CATEGORY_OPENABLE)
        type = "application/pdf"
    }
    startActivityForResult(intent,PICK_PDF_FILE)
}

2-）我现在有一个URI。我正在尝试将其转换为文件。然后我尝试获取字节。

override fun onActivityResult(requestCode: Int,resultCode: Int,resultData: Intent?) {
    super.onActivityResult(requestCode,resultCode,resultData)

    if (requestCode == PICK_PDF_FILE && resultCode == Activity.RESULT_OK) {
        resultData?.data?.also { documentUri ->
            contentResolver.takePersistableuriPermission(
                documentUri,Intent.FLAG_GRANT_READ_URI_PERMISSION
            )
            var file = documentUri.toFile(); // I am trying to convert URI to FILE type. //ERROR LINE
            Log.d("test",file.readBytes().toString()) // I'm trying to read the bytes.
        }
    }
}

但是这个错误：

 Caused by: java.lang.IllegalArgumentException: Uri lacks 'file' scheme: 
 content://com.android.externalstorage.documents/document/primary%3ADCIM%2Ftest.pdf

解决方法

考虑使用TaskCompletionSource异步加载文件作为输入流：

TaskCompletionSource<Stream> tcs = new TaskCompletionSource<>();

在openFile（）中：

if (tcs == null || tcs.Task.isCompleted || tcs.Task.isCanceled)
{
   startActivityForResult(Intent.createChooser(intent,"Select Document"),PICK_PDF_FILE);
   return tcs.getTask;
}
else
{
   return tcs.getTask;
}

在onActivityResult中：

if (requestCode == PICK_PDF_FILE && resultCode == Activity.RESULT_OK) {
   Uri uri = data.getData();
   tcs.setResult().getContentResolver().openInputStream(uri); 
}
else {
   tcs.setResult(null);
}

一旦有了InputStream，就可以将inputStream转换为字节数组： Convert InputStream to byte array in Java

但是，根据您需要对字节做些什么，您可以直接使用流。例如，如果您要转换PDF，则可以使用LEADTOOLS CloudServices库： https://www.leadtools.com/support/forum/posts/t12369-

File file = new File(path);
int size = (int) file.length();
byte[] bytes = new byte[size];
try {
    BufferedInputStream buf = new BufferedInputStream(new FileInputStream(file));
    buf.read(bytes,bytes.length);
    buf.close();
} catch (FileNotFoundException e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
} catch (IOException e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
}

来源：Android : How to read file in bytes?