如何使用Android API下载Google驱动器文件

以下程序将显示来自Google驱动器的“与您共享的文件”。我在listView中显示所有文件，在这里我想每当用户单击列表项时下载google驱动器文件，并且我编写了代码以获取文件的驱动器ID。

这就是我在以下代码中所做的。

每当用户使用Google Drive Android API单击列表项时，请帮助我从Google Drive下载文件。

public class MainActivity extends BaseDemoActivity{ 
private static final String TAG = "MainActivity";
private ListView mResultsListView;
private ResultsAdapter mResultsAdapter;
private ProgressBar mProgressBar;
private DriveId mSelectedFileDriveId;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    mResultsListView = (ListView) findViewById(R.id.listViewSamples);
    mResultsAdapter = new ResultsAdapter(this);
    mResultsListView.setAdapter(mResultsAdapter);

    mResultsListView.setOnItemClickListener(new OnItemClickListener() {

        @Override
        public void onItemClick(AdapterView<?> parent, View view,
                int position, long id) {
                 if (mSelectedFileDriveId != null) {
                        open();
                        return;
                    }
            }


    });
}
private void open() {
    showMessage("Select files drive id = "+mSelectedFileDriveId);
    // Reset progress dialog back to zero as we're
    // initiating an opening request.
   // mProgressBar.setProgress(0);
    DownloadProgressListener listener = new DownloadProgressListener() {
        @Override
        public void onProgress(long bytesDownloaded, long bytesExpected) {
            // Update progress dialog with the latest progress.
            int progress = (int)(bytesDownloaded*100/bytesExpected);
            Log.d(TAG, String.format("Loading progress: %d percent", progress));
            mProgressBar.setProgress(progress);
        }
    };

    Drive.DriveApi.getFile(getGoogleApiClient(), mSelectedFileDriveId)
        .open(getGoogleApiClient(), DriveFile.MODE_READ_WRITE, listener)
        .setResultCallback(driveContentsCallback);
    mSelectedFileDriveId = null;

}

private ResultCallback<DriveContentsResult> driveContentsCallback =
        new ResultCallback<DriveContentsResult>() {
    @Override
    public void onResult(DriveContentsResult result) {
        if (!result.getStatus().isSuccess()) {
            showMessage("Error while opening the file contents");
            return;
        }
        showMessage("File contents opened");       
    }
};

/**
 * Clears the result buffer to avoid memory leaks as soon as the activity is no longer
 * visible by the user.
 */
@Override
protected void onStop() {
    super.onStop();
    mResultsAdapter.clear();
}

@Override
public void onConnected(Bundle connectionHint) {
    super.onConnected(connectionHint); 
   Drive.DriveApi.requestSync(getGoogleApiClient())
   .setResultCallback(statusCallback);
    showMessage("Connecting ...");
}

final private ResultCallback<Status> statusCallback =
        new ResultCallback<Status>() {
            @Override
            public void onResult(Status arg0) {
                // TODO Auto-generated method stub
             showMessage("Fetching...");
             if(arg0.getStatus().isSuccess()){
                 Query query = new Query.Builder()
                    .addFilter(Filters.sharedWithMe())
                    .build();

                 Drive.DriveApi.query(getGoogleApiClient(), query)
                 .setResultCallback(metadataCallback);
             }else{
                 showMessage("Error = "+arg0);
             }
        }
};

final private ResultCallback<DriveApi.MetadataBufferResult> metadataCallback = 
        new ResultCallback<DriveApi.MetadataBufferResult>() {
            @Override
            public void onResult(DriveApi.MetadataBufferResult result) {
                // TODO Auto-generated method stub
                showMessage("onResult ...");
                if (!result.getStatus().isSuccess()) {
                    showMessage("Problem while retrieving results");
                    return;
                }
                mResultsAdapter.clear();
                mResultsAdapter.append(result.getMetadataBuffer());
                MetadataBuffer buffer = result.getMetadataBuffer();
                Metadata meta = buffer.get(0);
                Log.v(TAG,"WEB CONTENT LINK = "+meta.getWebContentLink());
                mSelectedFileDriveId = (DriveId) meta.getDriveId();
                showMessage("Count = "+mResultsAdapter.getCount());
            }
        };  

}