okhttp。无法保存加载的数据

Question

我无法保存从okhttp加载的数据。我的代码有什么问题。当我尝试在Log app崩溃时加载数据。请帮助。

public class MainActivity extends AppCompatActivity {
private static final String URL = "https://chroniclingamerica.loc.gov/search/titles/results/?terms=michigan&format=json&page=5";
private String data;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    loadData();
    Log.d("DATA", data);
}

private void loadData() {
    OkHttpClient client = new OkHttpClient();
    Request request = new Request.Builder()
            .url(URL)
            .build();
    Call call = client.newCall(request);
    call.enqueue(new Callback() {
        @Override
        public void onFailure(Call call, IOException e) {

        }

        @Override
        public void onResponse(Call call, Response response) throws IOException {
            data = response.body().string();
        }
    });
}

}

Answer 1

说明

问题在于您的代码是如何执行的（即同步与异步）。

您调用的方法loadData()不会像您期望的那样设置类属性数据 - 一旦获得响应，它将设置属性data但是函数loadData将不等待响应（即它不阻止当前线程或执行代码。）。这意味着在下一行LOG.d("Data", data);上，数据尚未设置，因此为空（并且会使您的应用崩溃）。

解决方案

如果您只想记录数据，那么只需在onResponse回调中分配日志语句后再移动它。

private void loadData() {
    OkHttpClient client = new OkHttpClient();
    Request request = new Request.Builder()
            .url(URL)
            .build();
    Call call = client.newCall(request);
    call.enqueue(new Callback() {
        @Override
        public void onFailure(Call call, IOException e) {
            // Some error has occurred
        }

        @Override
        public void onResponse(Call call, Response response) throws IOException {   
            processData(response.body().string());
        }
    });
}

private void processData(String data) {
    Log.d("DATA", data);
    // To other stuff here given your value data. 
}