同步方法/同步块不起作用

Question

我已经尝试了两种方法：同步方法和同步块上的同步块作为LOCK不能同时运行它们，但它似乎对我不起作用。

public class PagingBoundaryCallback extends PagedList.BoundaryCallback<Crypto> {

private static final String LOG_TAG = PagingBoundaryCallback.class.getSimpleName();
private static final String TAG_COIN_MARKET_CAP_API = LOG_TAG + CoinMarketCapApi.class.getSimpleName();
private static final String TAG_CRYPTO_COMPARE_API = LOG_TAG + CryptoCompareApi.class.getSimpleName();

private static final int RESULTS_SIZE = 50;
private static final String TO_SYMBOL = "USD";
private static final int FAVOURITE_FALSE = 0;
private static final Object LOCK = new Object();

private CoinMarketCap coinMarketCapApi;
private CryptoCompare cryptoCompareApi;
private CryptoLocalCache cache;

private int resultsFromRank = 1;
private boolean requestingInProgress = false;

private List<CryptoSimple> cryptoSimpleList;
private List<CryptoDetailed> cryptoDetailedList;
private List<Crypto> cryptoList = new ArrayList<>();

public PagingBoundaryCallback(
        CoinMarketCap coinMarketCapApi,
        CryptoCompare cryptoCompareApi,
        CryptoLocalCache cache) {
    this.coinMarketCapApi = coinMarketCapApi;
    this.cryptoCompareApi = cryptoCompareApi;
    this.cache = cache;
}

@Override
public void onZeroItemsLoaded() {
    super.onZeroItemsLoaded();
    requestAndSaveData();
}

@Override
public void onItemAtEndLoaded(Crypto itemAtEnd) {
    super.onItemAtEndLoaded(itemAtEnd);
    requestAndSaveData();
}

private void requestAndSaveData() {
    if (requestingInProgress) return;

    requestingInProgress = true;
    requestCryptoSimple();
    requestCryptoDetailed();
    createCryptoFromResponses(cryptoSimpleList, cryptoDetailedList);
    requestingInProgress = false;
}

private void requestCryptoSimple() {
    synchronized (LOCK) {
        coinMarketCapApi.requestCoins(resultsFromRank, RESULTS_SIZE).enqueue(
                new Callback<CryptoSimpleResponse>() {

                    @Override
                    public void onFailure(Call<CryptoSimpleResponse> call, Throwable t) {
                        Log.d(TAG_COIN_MARKET_CAP_API, "failed to get data");
                        Log.d(TAG_COIN_MARKET_CAP_API, "Unknown error " + t.getMessage());
                    }

                    @Override
                    public void onResponse(Call<CryptoSimpleResponse> call, Response<CryptoSimpleResponse> response) {
                        Log.d(TAG_COIN_MARKET_CAP_API, "got response: " + response.toString());
                        if (response.isSuccessful()) {
                            cryptoSimpleList = new ArrayList<>();
                            HashMap<String, CryptoSimple> hashMap = response.body().getItems();
                            for (Map.Entry<String, CryptoSimple> entry : hashMap.entrySet()) {
                                CryptoSimple cryptoSimple = entry.getValue();
                                cryptoSimpleList.add(cryptoSimple);
                                Log.v("CryptoSimple HashMap", cryptoSimple.toString());
                            }

                            Log.v("cryptoSimpleListSize", String.valueOf(cryptoSimpleList.size()));
                            resultsFromRank += RESULTS_SIZE;
                        } else {
                            Log.d(TAG_COIN_MARKET_CAP_API, "Unknown error " + response.errorBody().toString());
                        }
                    }
                }
        );
    }
}

private void requestCryptoDetailed() {
    synchronized (LOCK) {
        StringBuilder cryptoSymbol = new StringBuilder(RESULTS_SIZE);
        Log.v("cryptoSimpleListSize", String.valueOf(cryptoSimpleList.size()));

        for (CryptoSimple item : cryptoSimpleList) {
            cryptoSymbol
                    .append(item.getSymbol())
                    .append(",");
        }

        int cryptoSymbolLength = cryptoSymbol.length();
        Log.v("cryptoSymbolLength", String.valueOf(cryptoSymbolLength));
        String fromSymbol = cryptoSymbol.delete(cryptoSymbolLength - 1, cryptoSymbolLength).toString();

        cryptoCompareApi.requestCoins(fromSymbol, TO_SYMBOL).enqueue(new Callback<CryptoDetailedResponse>() {
            @Override
            public void onResponse(Call<CryptoDetailedResponse> call, Response<CryptoDetailedResponse> response) {
                Log.d(TAG_CRYPTO_COMPARE_API, "got response: " + response.toString());
                if (response.isSuccessful()) {
                    cryptoDetailedList = response.body().getList();
                } else {
                    Log.d(TAG_COIN_MARKET_CAP_API, "Unknown error " + response.errorBody().toString());
                }
            }

            @Override
            public void onFailure(Call<CryptoDetailedResponse> call, Throwable t) {
                Log.d(TAG_CRYPTO_COMPARE_API, "failed to get data");
                Log.d(TAG_CRYPTO_COMPARE_API, "Unknown error " + t.getMessage());
            }
        });
    }
}

private void createCryptoFromResponses(List<CryptoSimple> cryptoSimpleList, List<CryptoDetailed> cryptoDetailedList) {
    if (cryptoList.size() != 0)
        cryptoList.clear();
    for (int i = 0; i < cryptoSimpleList.size(); i++) {
        Crypto cryptoItem = new Crypto(
                cryptoSimpleList.get(i).getId(),
                cryptoSimpleList.get(i).getName(),
                cryptoSimpleList.get(i).getSymbol(),
                cryptoSimpleList.get(i).getRank(),
                cryptoDetailedList.get(i).getPrice(),
                cryptoDetailedList.get(i).getTime(),
                cryptoDetailedList.get(i).getVolume(),
                cryptoDetailedList.get(i).getChangePercentage(),
                cryptoDetailedList.get(i).getMarketCap(),
                FAVOURITE_FALSE
        );
        cryptoList.add(cryptoItem);
    }
    if (cryptoList.size() > 0)
        cache.insertCoins(cryptoList);
    Log.v(LOG_TAG, "Inserted " + String.valueOf(cryptoList.size()) + " to database");
}}

来自requestCryptoDetailed（）的

cryptoSimpleList;在将项目添加到requestCryptoSimple（）中的cryptoSimpleList之前访问;这就是我得到NullPointerException的原因。就像我说的那样，我已经尝试了两种方法：同一个对象上的同步方法和同步块，但它似乎对我不起作用。

如何运行整个requestCryptoSimple（）; requestCryptoDetailed（）之前的方法;方法