Question

我正在尝试从firebase存储中下载图像并在下载后显示图像。有没有办法在下载完成后返回我的方法？

这是我方法的代码：

public void downloadImagesFromFireStorage(final String couponName, String imgName) {

    finish = false;

    StorageReference storageRef = FirebaseStorage.getInstance()
        .getReferenceFromUrl("gs://xxxxx.appspot.com").child("imgs").child(imgName);

    final long ONE_MEGABYTE = 1024 * 1024;

    storageRef.getBytes(ONE_MEGABYTE).addOnSuccessListener(new OnSuccessListener<byte[]>() {    
        @Override
        public void onSuccess(byte[] bytes) {
            Bitmap bitmap = BitmapFactory.decodeByteArray(bytes, 0, bytes.length);
            saveBitmap(couponName, bitmap);
        }
    });

    final ProgressDialog progressDialog = new ProgressDialog(context);
    progressDialog.setTitle("Downloading..");
    progressDialog.setMessage("Now download " + couponName + "....");
    progressDialog.show();
}

Answer 1

是的，你可以，但我不推荐它，你可以添加while循环，在finish标志变为true之前不做任何事情，你需要在onFailure上听取更改{{ 1}}标志

finish

Answer 2

我建议您使用OnCompleteListener来确定任务是否完成。例如，

StorageReference storageRef = FirebaseStorage.getInstance()
                .getReferenceFromUrl("gs://xxxxx.appspot.com").child("imgs");
        final long ONE_MEGABYTE = 1024 * 1024;
        storageRef.getBytes(ONE_MEGABYTE).addOnSuccessListener(this, new OnSuccessListener<byte[]>() {
            @Override
            public void onSuccess(byte[] bytes) {

            }
        }).addOnCompleteListener(this, new OnCompleteListener<byte[]>() {
            @Override
            public void onComplete(@NonNull Task<byte[]> task) {
                if (task.isSuccessful()){
                      // do your work
                }
            }
        });

修改

根据Firebase文档，OnCompleteListener在任务完成时调用。它的公共方法onComplete返回已完成的任务（永不为null）。例如，

addOnCompleteListener(new OnCompleteListener<byte[]>() { @Override public void onComplete(@NonNull Task<byte[]> task) { //here, task is completed task returned by onComplete. } });

当任务成功完成时，OnSuccessListener被调用。它的方法是公共方法onSuccess返回任务的结果。例如，

addOnSuccessListener(new OnSuccessListener<byte[]>() { @Override public void onSuccess(byte[] bytes) { //here, bytes are the result that you are downloading or uploading } });

Answer 3

我宁愿使用SettableFuture来返回ListenableFuture。

private ListenableFuture<Void> downloadImage() {
    final SettableFuture<Void> future = SettableFuture.create();

    StorageReference storageRef = FirebaseStorage.getInstance()
        .getReferenceFromUrl("gs://xxxxx.appspot.com").child("imgs").child(imgName);

    final long ONE_MEGABYTE = 1024 * 1024;
    //performing the task on a background thread
    threadPoolService.schedule(new Runnable() {
        @Override
        public void run() {
            storageRef.getBytes(ONE_MEGABYTE).addOnSuccessListener(new OnSuccessListener<byte[]>() {    
                @Override
                public void onSuccess(byte[] bytes) {
                    Bitmap bitmap = BitmapFactory.decodeByteArray(bytes, 0, bytes.length);
                    saveBitmap(couponName, bitmap);
                    future.set(null);
                }
            });
        }
    });
    return future;
}

并在结果可用时添加回调。

final ProgressDialog progressDialog = new ProgressDialog(context);
progressDialog.setTitle("Downloading..");
progressDialog.setMessage("Now download " + couponName + "....");
progressDialog.show();
Futures.addCallback(downloadImage(), new FutureCallback<Void>() {
        @Override
        public void onSuccess(@Nullable Void result) {
           progressDialog.dismiss();
        }

        @Override
        public void onFailure(Throwable t) {
            progressDialog.dismiss();
            Timber.e(t, "Error occurred while downloading image");
        }
    });

如果要下载多个图像，请为每个图像创建未来，例如

List<SettableFuture<Void>> futures = new ArrayList<>();
for() {
  futures.add(downloadImage())
}

然后在下载所有图像时附加回调：

Futures.successfulAsList

下载成功后返回方法

3 个答案: