改装onResponse时出现java.lang.NullPointerException错误

Question

你好，我是第一次使用Retrofit，但我似乎不能让它工作。在开发一个可以获得本地货币的加密货币汇率的应用程序时，下面是link，JSON格式的api。

{
  "BTC": {
    "USD": 6019.1,
    "EUR": 5139.44,
    "NGN": 2136243.25
  },
  "ETH": {
    "USD": 290.98,
    "EUR": 250.03,
    "NGN": 103031.01
  }
}

以下是我的模型(来自http://www.jsonschema2pojo.org/)：更新

public class CryptoCurrency {

@SerializedName("BTC")
@Expose
private BTC BTC;
@SerializedName("ETH")
@Expose
private ETH ETH;

public BTC getBTC() {
    return BTC;
}

public void setBTC(BTC BTC) {
    this.BTC = BTC;
}

public ETH getETH() {
    return ETH;
}

public void setETH(ETH ETH) {
    this.ETH = ETH;
}

public class BTC {

    @SerializedName("USD")
    @Expose
    private Double USD;

    @SerializedName("EUR")
    @Expose
    private Double EUR;

    @SerializedName("NGN")
    @Expose
    private Double NGN;

    public Double getUSD() {
        return USD;
    }

    public void setUSD(Double USD) {
        this.USD = USD;
    }

    public Double getEUR() {
        return EUR;
    }

    public void setEUR(Double EUR) {
        this.EUR = EUR;
    }

    public Double getNGN() {
        return NGN;
    }

    public void setNGN(Double NGN) {
        this.NGN = NGN;
    }


}


public class ETH {

    @SerializedName("USD")
    @Expose
    private Double USD;
    @SerializedName("EUR")
    @Expose
    private Double EUR;
    @SerializedName("NGN")
    @Expose
    private Double NGN;

    public Double getUSD() {
        return USD;
    }

    public void setUSD(Double USD) {
        this.USD = USD;
    }

    public Double getEUR() {
        return EUR;
    }

    public void setEUR(Double EUR) {
        this.EUR = EUR;
    }

    public Double getNGN() {
        return NGN;
    }

    public void setNGN(Double NGN) {
        this.NGN = NGN;
    }

}

}

我的界面：

public interface CurrencyInterface {
    @GET("/data/pricemulti/")
    Call<CryptoCurrency.BTC> currency(@Query("crypto") String crypto, @Query("local") String local);
}

我的onResponse方法：

call.enqueue(new Callback<CryptoCurrency.BTC>() {
        @Override
        public void onResponse(Call<CryptoCurrency.BTC> call, Response<CryptoCurrency.BTC> response) {
            String currency = response.body().toString();
            Toast.makeText(getApplicationContext(), "result " + currency, Toast.LENGTH_LONG).show();
            Log.i("MainActivity", currency);

        }

        @Override
        public void onFailure(Call<CryptoCurrency.BTC> call, Throwable t) {

        }
    });

当我运行代码并检查我的日志时，我得到了这个错误：

java.lang.NullPointerException
at com.example.raynold.cryptorates.MainActivity$1.onResponse(MainActivity.java:53)
at retrofit2.ExecutorCallAdapterFactory$ExecutorCallbackCall$1$1.run(ExecutorCallAdapterFactory.java:70)

更新

我的MainActivity类

public class MainActivity extends AppCompatActivity {

private RecyclerView mCurrencyRecycler;
private Button mclickMe;
private CurrencyAdapter mCurrencyAdapter;
private List<CryptoCurrency> mCurrencyList;
private CurrencyInterface mCurrencyInterface;
private LinearLayoutManager mLinearLayoutManager;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    mCurrencyRecycler = (RecyclerView) findViewById(R.id.rv_rates);
    mLinearLayoutManager = new LinearLayoutManager(this);
    mCurrencyRecycler.setLayoutManager(mLinearLayoutManager);
    mCurrencyRecycler.setHasFixedSize(true);
    mclickMe = (Button) findViewById(R.id.click_me);

    mCurrencyInterface = ApiClient.getApiClient().create(CurrencyInterface.class);

    Call<CryptoCurrency.BTC> call = mCurrencyInterface.currency("BTC", "NGN");

    call.enqueue(new Callback<CryptoCurrency.BTC>() {
        @Override
        public void onResponse(Call<CryptoCurrency.BTC> call, Response<CryptoCurrency.BTC> response) {
            String currency = response.body().toString();
            Toast.makeText(getApplicationContext(), "result " + currency, Toast.LENGTH_LONG).show();
            Log.i("MainActivity", currency);

        }

        @Override
        public void onFailure(Call<CryptoCurrency.BTC> call, Throwable t) {

        }
    });

    mclickMe.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {

        }
    });

}

}

我还想知道如何让JSON使用循环视图，因为JSON是对象类型，而不是数组。

Answer 1

public class CryptoCurrency {

        @SerializedName("BTC")
        @Expose
        private BTC BTC;
        @SerializedName("ETH")
        @Expose
        private ETH ETH;

        public BTC getBTC() {
            return BTC;
        }

        public void setBTC(BTC BTC) {
            this.BTC = BTC;
        }

        public ETH getETH() {
            return ETH;
        }

        public void setETH(ETH ETH) {
            this.ETH = ETH;
        }

    class ETH {
      ...
    }

    class BTC {
       ...
    }

}

在您界面中使用CurrencyInterface，如下所示

@GET("/data/pricemulti")
Call<CryptoCurrency> currency(@Query("fsyms") String crypto, @Query("tsyms") String local);

处理方式类似

Call<CryptoCurrency> call = mCurrencyInterface.currency("BTC", "NGN");

call.enqueue(new Callback<CryptoCurrency>() {
        @Override
        public void onResponse(Call<CryptoCurrency> call, Response<CryptoCurrency> response) {
            BTC btc = response.body().getBTC();
            Toast.makeText(getApplicationContext(), "result " + btc.getNGN(), Toast.LENGTH_LONG).show();

        }

        @Override
        public void onFailure(Call<CryptoCurrency.BTC> call, Throwable t) {

        }
    });

Answer 2

如下所示更改您的onResponse方法：

...........
call.enqueue(new Callback<CryptoCurrency.BTC>() {
        @Override
        public void onResponse(Call<CryptoCurrency.BTC> call, Response<CryptoCurrency.BTC> response) {
            String currency = response.getUSD().toString();
            Toast.makeText(getApplicationContext(), "result " + currency, Toast.LENGTH_LONG).show();
            Log.i("MainActivity", currency);

        }

        @Override
        public void onFailure(Call<CryptoCurrency.BTC> call, Throwable t) {

        }
    });

试试这个来解决你的问题。

Answer 3

您不应该在URL的开头和结尾使用反斜杠。

尝试

@GET("data/pricemulti")

而不是

@GET("/data/pricemulti/")