SAF - DocumentFile 方法 findFile() 在子文件夹上不可能

Question

我的 Android 应用程序想要在 SAF 文件夹中多次写入同名的文本文件。 该文件必须替换为新版本。

由于 SAF 创建了重复文件，即它不会覆盖同名文件，并创建一个编号的文件名（文件，文件（1），...），以下方法必须在再次创建文件之前删除文件：

static public boolean writeTextDocumentInFolderUri(Activity activity,String folderUriString,String fileName,String mimetype, String text)
{
    boolean result;

    ContentResolver resolver=activity.getContentResolver();
    Uri uri = Uri.parse(folderUriString);
    Log.d("write dir",uri.toString());
    String docId = DocumentsContract.getDocumentId(uri);
    Log.d("write id",docId);
    Uri dirUri = DocumentsContract.buildDocumentUriUsingTree(uri, docId );
    Log.d("write dir uri",dirUri.toString());
    Uri destUri = null;

    DocumentFile dfDir=DocumentFile.fromTreeUri(activity,uri);
    Log.d("write fdir",dfDir.getUri().toString());
    DocumentFile df=dfDir.findFile(fileName);

    if (df!=null)
    {   
    Log.d("write df",df.getUri().toString());
    dfDir.findFile(fileName).delete();
    }

    try
    {
        destUri = DocumentsContract.createDocument(resolver, dirUri, mimetype, fileName);

    } catch (FileNotFoundException e )
    {


        return false;
    }

    try {
        ParcelFileDescriptor pfd=resolver.openFileDescriptor(destUri, "w");
        FileOutputStream fos=new FileOutputStream(pfd.getFileDescriptor());
        OutputStreamWriter writer = new OutputStreamWriter(fos);
        writer.append(text);
        writer.flush();
        writer.close();
        result= true;
    } catch (FileNotFoundException e) {
        result=false;
    } catch (IOException e) {
        result=false;
    }

    return result;
}

我得到这个日志：

write log dir: content://com.android.providers.downloads.documents/tree/raw%3A%2Fstorage%2Femulated%2F0%2FDownload%2Ffoldername/document/raw%3A%2Fstorage%2Femulated%2F0%2FDownload%2Ffoldername%2Fsubfoldername
write log id: raw:/storage/emulated/0/Download/sc notes/subfoldername
write log dir uri: content://com.android.providers.downloads.documents/tree/raw%3A%2Fstorage%2Femulated%2F0%2FDownload%2Ffoldername/document/raw%3A%2Fstorage%2Femulated%2F0%2FDownload%2Ffoldername%2Fsubfoldername
write log fdir: content://com.android.providers.downloads.documents/tree/raw%3A%2Fstorage%2Femulated%2F0%2FDownload%2Ffoldername/document/raw%3A%2Fstorage%2Femulated%2F0%2FDownload%2Ffoldername

正如你所看到的那样

DocumentFile dfDir=DocumentFile.fromTreeeUri(activity,uri);

产生父文件夹，而不是子文件夹。 我需要这一行才能使用 findFile 方法。

相反，如果我将其替换为

DocumentFile dfDir=DocumentFile.fromSingleUri(activity,uri);

我收到一个错误，因为它不被视为目录

 java.lang.UnsupportedOperationException
    at android.support.v4.provider.SingleDocumentFile.listFiles(SingleDocumentFile.java:115)
    at android.support.v4.provider.DocumentFile.findFile(DocumentFile.java:338)
    at com.appname.app.SAFUtils.writeTextDocumentInFolderUri(SAFUtils.java:341)

在

DocumentFile df=dfDir.findFile(fileName);


write log dir: content://com.android.providers.downloads.documents/tree/raw%3A%2Fstorage%2Femulated%2F0%2FDownload%2Ffoldername/document/raw%3A%2Fstorage%2Femulated%2F0%2FDownload%2Ffoldername%2Fsubfoldername
write log id: raw:/storage/emulated/0/Download/sc notes/subfoldername
write log dir uri: content://com.android.providers.downloads.documents/tree/raw%3A%2Fstorage%2Femulated%2F0%2FDownload%2Ffoldername/document/raw%3A%2Fstorage%2Femulated%2F0%2FDownload%2Ffoldername%2Fsubfoldername
write log fdir: content://com.android.providers.downloads.documents/tree/raw%3A%2Fstorage%2Femulated%2F0%2FDownload%2Ffoldername/document/raw%3A%2Fstorage%2Femulated%2F0%2FDownload%2Ffoldername%2Fsubfoldername

怎么了？