使用Retrofit2.0实现Google Drive文件上传进度显示

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在上一篇文章中，我们完成了Retrofit2.0接口的定义及基本的调用。
不知大家是否关注到DriveApi.uploadFileMutil()这个接口方法需要传入两个MultipartBody.Part对象，分别对应Metadata part和Media part，如何实现这里的Part对象呢？分为两部分：

Metadata Part

这部分比较简单，MultipartBody.Part.create()方法直接创建即可：

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String content = "{\"name\": \"" + fileName + "\"}";
MediaType contentType = MediaType.parse("application/json; charset=UTF-8");
MultipartBody.Part metaPart =
        MultipartBody.Part.create(RequestBody.create(contentType, content));

Media Part

需要我们自己实现一个RequestBody对象，并重写里面的contentType()和writeTo()方法。代码可以参考StackOverflow上的这个回答：Is it possible to show progress bar when upload image via Retrofit 2

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public class ProgressRequestBody extends RequestBody {
    private File mFile;
    private String mPath;
    private UploadCallbacks mListener;

    private static final int DEFAULT_BUFFER_SIZE = 2048;

    public interface UploadCallbacks {
        void onProgressUpdate(int percentage);
        void onError();
        void onFinish();
    }

    public ProgressRequestBody(final File file, final  UploadCallbacks listener) {
        mFile = file;
        mListener = listener;            
    }

    @Override
    public MediaType contentType() {
        // i want to upload only images
        return MediaType.parse("image/*");
    }

    @Override
    public void writeTo(BufferedSink sink) throws IOException {
        long fileLength = mFile.length();
        byte[] buffer = new byte[DEFAULT_BUFFER_SIZE];
        FileInputStream in = new FileInputStream(mFile);
        long uploaded = 0;

        try {
            int read;
            Handler handler = new Handler(Looper.getMainLooper());
            while ((read = in.read(buffer)) != -1) {

                uploaded += read;
                sink.write(buffer, 0, read);
                // update progress on UI thread
                handler.post(new ProgressUpdater(uploaded, fileLength));
            }
        } finally {
            in.close();
        }
    }

    private class ProgressUpdater implements Runnable {
        private long mUploaded;
        private long mTotal;
        public ProgressUpdater(long uploaded, long total) {
            mUploaded = uploaded;
            mTotal = total;
        }

        @Override
        public void run() {
            mListener.onProgressUpdate((int)(100 * mUploaded / mTotal));            
        }
    }
}

注意SO这个回答贴出的代码还有点问题，下面这句应该放在while循环的最下面，否则你最后一直只能收到99%。

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// update progress on UI thread
handler.post(new ProgressUpdater(uploaded, fileLength));

Callback

然后实现UploadCallbacks接口里的相关回调即可：

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class MyActivity extends AppCompatActivity implements ProgressRequestBody.UploadCallbacks {
    ProgressBar progressBar;
    ProgressRequestBody mBody;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        progressBar = findViewById(R.id.progressBar);
        mBody = new ProgressRequestBody(mFile, this);
    }

    @Override
    public void onProgressUpdate(int percentage) {
        // set current progress
        progressBar.setProgress(percentage);
    }

    @Override
    public void onError() {
        // do something on error
    }

    @Override
    public void onFinish() {
        // do something on upload finished
        // for example start next uploading at queue
        progressBar.setProgress(100);
    }

}

最后同样调用MultipartBody.Part.create()创建即可：

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MultipartBody.Part dataPart = MultipartBody.Part.create(mBody);