Question

我正在学习使用REST API来创建一个使用雅虎天气来显示今天天气的应用程序。我创建了一个AsyncTask，一个自定义适配器和一个我在MainActivity中调用的WeatherData类。我在使用这个WeatherData类和自定义适配器时遇到了一些麻烦。

在我尝试从我的天气数据类调用JSON对象时，在适配器中出现错误。它表示无法从静态上下文中引用非静态字段“weather”和“date”。我试图阅读静态上下文，但它确实让我感到困惑的是它是什么以及它做了什么。

第二个问题是当我尝试将日期和天气添加到我的weatherdata ArrayList时，我的AsyncTask现在也会出错。它说WeatherData中的WeatherData（JSONobject）不能应用于JSONObject，java.lang.String。我认为这与我在WeatherData类中使用天气和日期作为对象这一事实有关，然后尝试将它们用作我的arraylist中的字符串。我试图通过简单地将它们更改为WeatherData类中的字符串来修复它，但后来我得到了各种新错误。有人可以帮助我解决我的错误吗？

所以，这是我调用数据的MainActivity的一部分：

public void getData(View view) {
    ClassAsyncTask task = new ClassAsyncTask(this);
    task.execute(chosenloc);
}

public void setData(ArrayList<WeatherData> weatherdata) {
    // Construct the data source
    ArrayList<WeatherData> arrayOfWeather = new ArrayList<WeatherData>();
    // Create the adapter to convert the array to views
    CustomArrayAdapter adapter = new CustomArrayAdapter(this, arrayOfWeather);
    // Attach the adapter to a Listview
    ListView listView = (ListView) findViewById(R.id.weatherListView);
    listView.setAdapter(adapter);
}

这是我的自定义适配器：

public class CustomArrayAdapter extends ArrayAdapter<WeatherData> {
public CustomArrayAdapter(Context context, ArrayList<WeatherData> weatherdata){
    super(context, 0, weatherdata);
}

@Override
public View getView(int position, View convertView, ViewGroup parent){
    // Get the data item for this position
    WeatherData weather = getItem(position);
    // Check if an exising view is being reused, otherwise inflate the view
    if (convertView == null){
        convertView = LayoutInflater.from(getContext()).inflate(R.layout.custom_array_layout, parent, false);
    }
    // Lookup view for data population
    TextView date = (TextView) convertView.findViewById(R.id.date);
    TextView weather = (TextView) convertView.findViewById(R.id.weather);

    // Populate the data into the template view using the data object
    date.setText(WeatherData.date);
    weather.setText(WeatherData.weather);

    // Return the completed view to render on screen
    return convertView;
}
}

我的WeatherData类：

public class WeatherData {
// Fields
public JSONObject date;
public String weather;

// Constructor
public WeatherData(JSONObject object) {
    try {
        JSONArray dates = object.getJSONArray("date");
        JSONArray weather = object.getJSONArray("text");
    } catch (JSONException e) {
        e.printStackTrace();
    }
}
    // Method to convert an array of JSON objects into a list of objects
    public static ArrayList<WeatherData> fromJson(JSONArray jsonObjects){
        ArrayList<WeatherData> weather = new ArrayList<WeatherData>();
        for (int i = 0; i < jsonObjects.length(); i++) {
            try {
                weather.add(new WeatherData(jsonObjects.getJSONObject(i)));
            } catch (JSONException e) {
                e.printStackTrace();
            }
        }
        return weather;
    }
}

最后，我解析JSON的AsyncTask部分：

protected void onPostExecute(String result){
    super.onPostExecute(result);

    // Alert user if nothing was found
    if(result.length() == 0){
        Toast.makeText(context, "Nothing was found", Toast.LENGTH_SHORT).show();
    }
    else {
        // Parse JSON
        ArrayList<WeatherData> weatherdata = new ArrayList<>();
        try {
            JSONObject respObj = new JSONObject(result);
            JSONObject forecastObj = respObj.getJSONObject("forecast");
            JSONArray dates = forecastObj.getJSONArray("date");
            JSONArray weatherArray = forecastObj.getJSONArray("text");

            for (int i = 0; i<dates.length(); i++){
                JSONObject date = dates.getJSONObject(i);
                String weather = date.getString("text");
                weatherdata.add(new WeatherData(date, weather));
            }
        } catch (JSONException e) {
            e.printStackTrace();
        }
        // Update MainActivity
        this.activity.setData(weatherdata);
    }
}

Answer 1

你有很多语义错误，了解静态和非静态的差异和细微差别非常重要，但要修复你的代码，只需要注意你所使用的变量。我不会为你阅读雅虎天气API，所以我在这里以一般方式展示了一些东西。

固定代码如下：

这应该是您的getView

// Get the data item for this position
WeatherData weather = getItem(position);
// Check if an exising view is being reused, otherwise inflate the view
if (convertView == null){
    convertView = LayoutInflater.from(getContext()).inflate(R.layout.custom_array_layout, parent, false);
}
// CHANGED HERE the textView "weather` had the same name of the "WeatherData" defined a few lines above
// Lookup view for data population
TextView textDate = (TextView) convertView.findViewById(R.id.date);
TextView textWeather = (TextView) convertView.findViewById(R.id.weather);

// CHANGED HERE to properly call the textView methods and to read the fields from the instance of "WeatherData"
// Populate the data into the template view using the data object
textDate.setText(weather.date);
textWeather.setText(weather.weather);

// Return the completed view to render on screen
return convertView;

你的“WeatherData”构造函数也是不合逻辑的，会导致NPE。我不知道你在那里想要实现什么，但是当你写JSONArray dates = object...时，你提取的信息被添加到这个JsonArray然后就被扔掉了。字段public JSONObject date或public String weather永远不会初始化，也不包含任何有用的信息。您可能想要做的是这样的事情：

// Fields
public String val1;
public String val2;
public String val3;
  ... any value necessary

// Constructor
public WeatherData(JSONObject object) {
    try {
         val1 = object.optString("val1");
         val2 = object.optString("val2");
         val3 = object.optString("val3");
        ... parse here EVERYTHING from the object
    } catch (JSONException e) {
        e.printStackTrace();
    }
}

另外，在您的postExecute上，您尝试创建新的WeatherData向其传递两个值，例如new WeatherData(date, weather)。再次，阅读WeatherData构造函数，它只使用1个值，即JsonObject object。

最后一个是性能问题，您不应该将string返回到onPostExecute。你应该做一个返回ArrayList<WeatherData> result的AsyncTask。然后，所有解析代码都应该在background执行中。

编辑：示例asyncTask

   public class MyAsyncTask extends AsyncTask<String, Integer, List<WeatherObject>>{

      @Override protected List<WeatherObject> doInBackground(String... params) {
         // here you call the API and parse the results
         // return ArrayList<WeatherObject> if successful, or `null` if failed
         return null;
      }

      @Override protected void onPostExecute(List<WeatherObject> weatherObjectList) {
           // here you simply check for null and use the List
           if(weatherObjectList == null){
               // fail to load data
           } else {
               // set data to adapter
           }
      }
   }

对非静态字段和JSON对象感到困惑

1 个答案: