TestHelpers.java 文件源码

public static DataSnapshot getSnap(Query ref) throws InterruptedException {

    final Semaphore semaphore = new Semaphore(0);

    // Hack to get around final reference issue
    final List<DataSnapshot> snapshotList = new ArrayList<>(1);

    ref.addListenerForSingleValueEvent(
        new ValueEventListener() {
          @Override
          public void onDataChange(DataSnapshot snapshot) {
            snapshotList.add(snapshot);
            semaphore.release(1);
          }

          @Override
          public void onCancelled(DatabaseError error) {
            semaphore.release(1);
          }
        });

    semaphore.tryAcquire(1, TestUtils.TEST_TIMEOUT_MILLIS, TimeUnit.MILLISECONDS);
    return snapshotList.get(0);
  }