Question

我尝试运行以下代码，但android studio一直说保存字符串对象存在问题，但据我所知，代码编写正确。任何人都可以看到问题所在并帮助我解决问题吗？在最新的更新之后我对android studio有更多的问题，所以我很难弄清楚问题是由于我的代码在某处错误还是更新。

错误：（90,37）错误：没有为Intent（CityWeatherData，Class）构造函数找到合适的构造函数Intent.Intent（String，Uri）不适用（参数不匹配; CityWeatherData无法转换为String）构造函数Intent.Intent （Context，Class）不适用（参数不匹配; CityWeatherData无法转换为Context）

错误：（95,13）错误：找不到符号方法startActivity（Intent）

错误：任务'：app：compileDebugJavaWithJavac'的执行失败。＆GT;编译失败;有关详细信息，请参阅编译器错误输出。

我有一个类，它将OpenWeatherMap中的数据作为JSON对象获取，并将它们显示在Activity中。

非活动类：

public class CityWeatherData extends AsyncTask<String,Void,String> {
    @Override
    protected String doInBackground(String... urls) {

        String result = ""; //JSON data will be kept here when first downloaded
        URL url;
        HttpURLConnection urlConnection = null;

        //API set up in OpenWeatherMap
        //Try and catch used in case user does not have internet connection etc.
        try {
            url = new URL(urls[0]);
            urlConnection = (HttpURLConnection) url.openConnection();
            InputStream input = urlConnection.getInputStream();

            //Reader to read inputStream for URL
            InputStreamReader inputReader = new InputStreamReader(input);

            int data = inputReader.read(); //Data from stream is put into an int called data

            //When data finishes reading = -1 ; There for while loop need for data not equal to -1
            while (data != -1){

                char current = (char) data;
                result += current;
                data = inputReader.read();
            }

            return result;

        } catch (Exception e) {
            e.printStackTrace();
        }

        return null;
    }

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

        //Create JSON object from result
        try {
            JSONObject jsonObject = new JSONObject(result);
            JSONObject weatherData = new JSONObject(jsonObject.getString("main"));
            //The data we are interesed in is located after "main"

            //Get temp from main
            double temp = Double.parseDouble(weatherData.getString("temp"));

            //Temp is given i Kelvin so it needs to be converted to Celcius
            int tempInt = (int) (temp -273.15);

            //Get city name
            String placeName = jsonObject.getString("name");

            //Get description
            String weatherDescription = jsonObject.getString("description");

            //Get humidity
            double humidityValue = Double.parseDouble(weatherData.getString("humidity"));

            Intent sendDataIntent = new Intent(CityWeatherData.this, CityDetailsActivity.class);
            sendDataIntent.putExtra("tempData", tempInt);
            sendDataIntent.putExtra("cityNameData", placeName);
            sendDataIntent.putExtra("humidityData", humidityValue);
            sendDataIntent.putExtra("descriptionData", weatherDescription);

        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

活动类：

public class CityDetailsActivity extends AppCompatActivity {

    String placeName;
    int tempInt;
    double humidityValue;
    String weatherDescription;

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

        Bundle getData = getIntent().getExtras();
        if (getData !=null){
            int tempInt = getData.getInt("tempData");
            String placeName = getData.getString("cityNameData");
            double humidityValue = getData.getDouble("humidityData");
            String weatherDescription = getData.getString("descriptionData");

        }
    }

    @Override
    protected void onResume() {
        super.onResume();
        // Update with info from ShowData
        updateFields();
    }

    private void updateFields(){
        // Used to show data
        TextView city_name = findViewById(R.id.city_name);
        city_name.setText(placeName);
        TextView temp = findViewById(R.id.temp);
        temp.setText(String.valueOf(tempInt));
        TextView humidity = findViewById(R.id.humidity);
        humidity.setText(String.valueOf(humidityValue));
        TextView show_description = findViewById(R.id.show_description);
        show_description.setText(weatherDescription);
    }

    //Save current data in activity upon rotation
    @Override
    protected void onSaveInstanceState(Bundle outState) {
        super.onSaveInstanceState(outState);
    }
}

Answer 1

您的AsyncTask在没有实际启动活动的情况下接收参数。

编辑：对活动上下文使用弱引用。

private static class CityWeatherData extends AsyncTask<String,Void,String> {

        private WeakReference<MainActivity> mainActivity;    

        public CityWeatherData(MainActivity context) {   
            mainActivity = new WeakReference<>(context);            
        }

        @Override
        protected String doInBackground(String... urls) {
          ....
        }


        @Override
        protected void onPostExecute(String result) {
            super.onPostExecute(result);
            MainActivity cxt = mainActivity.get();
            if (cxt != null) {

            //Create JSON object from result
        try {
            JSONObject jsonObject = new JSONObject(result);
            JSONObject weatherData = new JSONObject(jsonObject.getString("main"));
            //The data we are interesed in is located after "main"

            //Get temp from main
            double temp = Double.parseDouble(weatherData.getString("temp"));

            //Temp is given i Kelvin so it needs to be converted to Celcius
            int tempInt = (int) (temp -273.15);

            //Get city name
            String placeName = jsonObject.getString("name");

            //Get description
            String weatherDescription = jsonObject.getString("description");

            //Get humidity
            double humidityValue = Double.parseDouble(weatherData.getString("humidity"));

            Intent sendDataIntent = new Intent(cxt, CityDetailsActivity.class);
            sendDataIntent.putExtra("tempData", tempInt);
            sendDataIntent.putExtra("cityNameData", placeName);
            sendDataIntent.putExtra("humidityData", humidityValue);
            sendDataIntent.putExtra("descriptionData", weatherDescription);
            startActivity(sendDataIntent);

        } catch (Exception e) {
            e.printStackTrace();
        }
      }
    }
}

android studio 3.0更新或错误代码导致的问题？

1 个答案: