我是开发Android应用程序的新手，我对Java知之甚少，所以我被困在这里：/ 我正在尝试创建一个新的FetchWeatherTask并在其上调用execute方法 你能告诉我怎么办才能使我的代码正常工作吗？
这是MainActivity.java
package com.example.android.sunshine33;
import android.os.Bundle;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
public class MainActivity extends AppCompatActivity {
private boolean hasOptionsMenu;
@Override
//onCreate is called to do initial creation of the fragment.
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
// Add this line in order for this fragment to handle menu events.
setHasOptionsMenu(true); //to indicate that we want call backs for the below methods
setContentView(R.layout.activity_main);
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
fab.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
.setAction("Action", null).show();
}
});
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_main, menu);
return true;
}
//how to handle clicks on my buttons,....
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
//noinspection SimplifiableIfStatement
if (id == R.id.action_refresh)
{
ForecastFragment.FetchWeatherTask weatherTask = new ForecastFragment.FetchWeatherTask();
weatherTask.execute();
return true;
}
return super.onOptionsItemSelected(item);
}
public void setHasOptionsMenu(boolean hasMenu) {
this.hasOptionsMenu = hasMenu;
}
}
这里是ForecastFragment.java
package com.example.android.sunshine33;
import android.os.AsyncTask;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;
import java.util.ArrayList;
/**
* A placeholder fragment containing a simple view.
*/
public class ForecastFragment extends Fragment {
public ForecastFragment() {
}
//onCreateView is where the UI gets initialized
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState)
{
ArrayList<String> forecastList = new ArrayList<String>()
{{
add("Today-Sunny-88/63");
add("Tomorrow-Foggy-70/46");
add("Weds-Cloudy-72/63");
add("Thurs-Rainy-64/51");
add("Fri-Foggy-70/46");
add("Sat-Sunny-76/68");
}};
ArrayAdapter<String> forecastAdapter = new ArrayAdapter<String>(
getActivity(), // The current context
R.layout.list_item_forecast, // The name of the layout ID. already mwgood fel prog
R.id.list_item_forecast_textview, // The ID of the textview to populate.
forecastList);
View rootview = inflater.inflate(R.layout.fragment_main, container, false); //msh fhmah??????????????
//binding between listView & adapter
ListView L = (ListView) rootview.findViewById(R.id.listview_forecast); //search for listView's ID
L.setAdapter(forecastAdapter); //b3ml set ll adapter 3la l mkan 2lli feh l listview
// These two need to be declared outside the try/catch
// so that they can be closed in the finally block.
HttpURLConnection urlConnection = null;
BufferedReader reader = null;
// Will contain the raw JSON response as a string.
String forecastJsonStr = null;
String mode="json";
String units="metric";
int DaysNumber=7;
try {
// Construct the URL for the OpenWeatherMap query
// Possible parameters are available at OWM's forecast API page, at
// http://openweathermap.org/API#forecast
String baseUrl = "http://api.openweathermap.org/data/2.5/forecast/daily?q=94043&mode=json&units=metric&cnt=7";
String apiKey = "&APPID=" +"bb30d8f31d6987dc5debd8ac4eddc989";
final String API_Key_Param="bb30d8f31d6987dc5debd8ac4eddc989";
final String City_ID_Param="q";
final String mode_Param=mode;
final String units_Param=units;
final int DaysNumber_Param=DaysNumber;
URL url = new URL(baseUrl.concat(apiKey));
// Create the request to OpenWeatherMap, and open the connection
urlConnection = (HttpURLConnection) url.openConnection();
urlConnection.setRequestMethod("GET");
urlConnection.connect();
// Read the input stream into a String
InputStream inputStream = urlConnection.getInputStream();
StringBuffer buffer = new StringBuffer();
if (inputStream == null) {
// Nothing to do.
return null;
}
reader = new BufferedReader(new InputStreamReader(inputStream));
String line;
while ((line = reader.readLine()) != null) {
// Since it's JSON, adding a newline isn't necessary (it won't affect parsing)
// But it does make debugging a *lot* easier if you print out the completed
// buffer for debugging.
buffer.append(line + "\n");
}
if (buffer.length() == 0) {
// Stream was empty. No point in parsing.
return null;
}
forecastJsonStr = buffer.toString();
} catch (IOException e) {
Log.e("PlaceholderFragment", "Error ", e);
// If the code didn't successfully get the weather data, there's no point in attempting
// to parse it.
return null;
} finally {
if (urlConnection != null) {
urlConnection.disconnect();
}
if (reader != null) {
try {
reader.close();
} catch (final IOException e) {
Log.e("PlaceholderFragment", "Error closing stream", e);
}
}
}
return rootview;
}
public class FetchWeatherTask extends AsyncTask<Void, Void, Void>
{
private final String LOG_TAG = FetchWeatherTask.class.getSimpleName();
@Override
protected Void doInBackground(Void... params)
{
// These two need to be declared outside the try/catch
// so that they can be closed in the finally block.
HttpURLConnection urlConnection = null;
BufferedReader reader = null;
// Will contain the raw JSON response as a string.
String forecastJsonStr = null;
try {
// Construct the URL for the OpenWeatherMap query
// Possible parameters are available at OWM's forecast API page, at
// http://openweathermap.org/API#forecast
URL url = new URL("http://api.openweathermap.org/data/2.5/forecast/daily?q=94043&mode=json&units=metric&cnt=7");
// Create the request to OpenWeatherMap, and open the connection
urlConnection = (HttpURLConnection) url.openConnection();
urlConnection.setRequestMethod("GET");
urlConnection.connect();
// Read the input stream into a String
InputStream inputStream = urlConnection.getInputStream();
StringBuffer buffer = new StringBuffer();
if (inputStream == null) {
// Nothing to do.
forecastJsonStr = null;
}
reader = new BufferedReader(new InputStreamReader(inputStream));
String line;
while ((line = reader.readLine()) != null) {
// Since it's JSON, adding a newline isn't necessary (it won't affect parsing)
// But it does make debugging a *lot* easier if you print out the completed
// buffer for debugging.
buffer.append(line + "\n");
}
if (buffer.length() == 0) {
// Stream was empty. No point in parsing.
return null;
}
forecastJsonStr = buffer.toString();
} catch (IOException e) {
Log.e(LOG_TAG, "Error ", e);
// If the code didn't successfully get the weather data, there's no point in attempting
// to parse it.
return null;
} finally {
if (urlConnection != null) {
urlConnection.disconnect();
}
if (reader != null) {
try {
reader.close();
} catch (final IOException e) {
Log.e(LOG_TAG, "Error closing stream", e);
}
}
}
return null;
}
}
}
答案 0 :(得分：0)
而不是：
public class FetchWeatherTask extends AsyncTask<Void, Void, Void>
使用：
public static class FetchWeatherTask extends AsyncTask<Void, Void, Void>
您未在 MainActivity 中实例化 ForecastFragment ;因此需要声明 FetchWeatherTask （这是 ForecastFragment 的嵌套类）静态
答案 1 :(得分：0)
是的，所以我的评论应该是正确的。你需要改变
public class ForecastFragment {
...
public class FetchWeatherTask {
...
}
}
到
public class ForecastFragment {
...
public static class FetchWeatherTask {
...
}
}
这是因为FetchWeatherClass，作为一个内部类（读取：你原来如何拥有它，没有静态），“is associated with an instance of its enclosing class...”而 static 嵌套类不是。