java - 下载成功后返回方法

Question

我正在尝试从 firebase 存储下载图像并在下载后显示图像。有没有办法下载完成后才返回我的方法？

这是我的方法的代码:

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

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
                }
            }
        });

编辑

根据 Firebase 文档，OnCompleteListener 在任务完成时调用。它的公共(public)方法 onComplete 返回完成的任务(永不为空)。例如，

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

而 OnSuccessListener 在任务成功完成时调用。它的方法公共(public)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
        }
    });