Java 应用程序不工作。它适用于android 5.1,但不适用于android 10.0
我刚听完讲座: 这是错误消息 E/AndroidRuntime:致命异常:主 进程:com.example.weather3,PID:8893 java.lang.NullPointerException:尝试在空对象引用上调用虚拟方法“boolean java.lang.String.containsjava.lang.CharSequence” 在com.example.weather3.MainActivity$GetWeather.onPostExecuteMainActivity.java:166 位于com.example.weather3.MainActivity$GetWeather.onPostExecuteMainActivity.java:142 位于android.os.AsyncTask.finishAsyncTask.java:755 在android.os.AsyncTask.access$900AsyncTask.java:192 在android.os.AsyncTask$InternalHandler.handleMessageAsyncTask.java:772 位于android.os.Handler.dispatchMessageHandler.java:107 在android.os.Looper.Looper.java:214 在android.app.ActivityThread.mainActivityThread.java:7356 在java.lang.reflect.Method.Invokenactive方法中 位于com.android.internal.os.RuntimeInit$MethodAndArgsCaller.RuntimeInit.java:492 位于com.android.internal.os.ZygoteInit.mainZygoteInit.java:930 这就是我在上面写的发生错误的部分Java 应用程序不工作。它适用于android 5.1,但不适用于android 10.0,java,android,android-asynctask,Java,Android,Android Asynctask,我刚听完讲座: 这是错误消息 E/AndroidRuntime:致命异常:主 进程:com.example.weather3,PID:8893 java.lang.NullPointerException:尝试在空对象引用上调用虚拟方法“boolean java.lang.String.containsjava.lang.CharSequence” 在com.example.weather3.MainActivity$GetWeather.onPostExecuteMainActivity.ja
@Override
protected void onPostExecute(String s) {
super.onPostExecute(s);
if(s.contains("Error: Not found city")){
pd.dismiss();
return;
}
Gson gson = new Gson();
Type mType = new TypeToken<OpenWeatherMap>(){}.getType();
openWeatherMap = gson.fromJson(s, mType);
pd.dismiss();
txtCity.setText(String.format("%s,%s",openWeatherMap.getName(),openWeatherMap.getSys().getCountry()));
txtLastUpdate.setText(String.format("Last Updated: %s", Common.getDateNow()));
txtDescription.setText(String.format("%s",openWeatherMap.getWeather().get(0).getDescription()));
txtHumidity.setText(String.format("%d%%",openWeatherMap.getMain().getHumidity()));
txtTime.setText(String.format("%s/%s",Common.unixTimeStampToDateTime(openWeatherMap.getSys().getSunrise()), Common.unixTimeStampToDateTime(openWeatherMap.getSys().getSunset())));
txtCelsius.setText(String.format("%.2f °C",openWeatherMap.getMain().getTemp()));
Picasso.with(MainActivity.this)
.load(Common.getImage(openWeatherMap.getWeather().get(0).getIcon()))
.into(imageView);
}
如果你需要帮助,这就是全部代码
package com.example.weather3;
import androidx.appcompat.app.AppCompatActivity;
import androidx.core.app.ActivityCompat;
import android.Manifest;
import android.app.ProgressDialog;
import android.content.Context;
import android.content.pm.PackageManager;
import android.location.Criteria;
import android.location.Location;
import android.location.LocationListener;
import android.location.LocationManager;
import android.os.AsyncTask;
import android.os.Bundle;
import android.util.Log;
import android.widget.ImageView;
import android.widget.TextView;
import com.example.weather3.Common.Common;
import com.example.weather3.Helper.Helper;
import com.example.weather3.Model.OpenWeatherMap;
import com.google.gson.Gson;
import com.google.gson.reflect.TypeToken;
import com.squareup.picasso.Picasso;
import java.lang.reflect.Type;
public class MainActivity extends AppCompatActivity implements LocationListener {
TextView txtCity, txtLastUpdate, txtDescription, txtHumidity, txtTime, txtCelsius;
ImageView imageView;
LocationManager locationManager;
String provider;
static double lat, lng;
OpenWeatherMap openWeatherMap = new OpenWeatherMap();
int MY_PERMISSION = 0;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
//Control
txtCity = (TextView) findViewById(R.id.txtCity);
txtLastUpdate = (TextView) findViewById(R.id.txtLastUpdate);
txtDescription = (TextView) findViewById(R.id.txtDescription);
txtHumidity = (TextView) findViewById(R.id.txtHumidity);
txtTime = (TextView) findViewById(R.id.txtTime);
txtCelsius = (TextView) findViewById(R.id.txtCelsius);
imageView = (ImageView) findViewById(R.id.imageView);
//Get Coordinates
locationManager = (LocationManager) getSystemService(Context.LOCATION_SERVICE);
provider = locationManager.getBestProvider(new Criteria(), false);
if (ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED && ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED) {
ActivityCompat.requestPermissions(MainActivity.this, new String[]{
Manifest.permission.INTERNET,
Manifest.permission.ACCESS_COARSE_LOCATION,
Manifest.permission.ACCESS_FINE_LOCATION,
Manifest.permission.ACCESS_NETWORK_STATE,
Manifest.permission.SYSTEM_ALERT_WINDOW,
Manifest.permission.WRITE_EXTERNAL_STORAGE
}, MY_PERMISSION);
}
Location location = locationManager.getLastKnownLocation(provider);
if (location == null) {
Log.e("TAG", "No Location");
}
}
protected void onPause() {
super.onPause();
if (ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED && ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED) {
ActivityCompat.requestPermissions(MainActivity.this, new String[]{
Manifest.permission.INTERNET,
Manifest.permission.ACCESS_COARSE_LOCATION,
Manifest.permission.ACCESS_FINE_LOCATION,
Manifest.permission.ACCESS_NETWORK_STATE,
Manifest.permission.SYSTEM_ALERT_WINDOW,
Manifest.permission.WRITE_EXTERNAL_STORAGE
}, MY_PERMISSION);
}
locationManager.removeUpdates(this);
}
protected void onResume() {
super.onResume();
if (ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED && ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED) {
ActivityCompat.requestPermissions(MainActivity.this, new String[]{
Manifest.permission.INTERNET,
Manifest.permission.ACCESS_COARSE_LOCATION,
Manifest.permission.ACCESS_FINE_LOCATION,
Manifest.permission.ACCESS_NETWORK_STATE,
Manifest.permission.SYSTEM_ALERT_WINDOW,
Manifest.permission.WRITE_EXTERNAL_STORAGE
}, MY_PERMISSION);
}
locationManager.requestLocationUpdates(provider, 400, 1, this);
}
@Override
public void onLocationChanged(Location location) {
lat=location.getLatitude();
lng=location.getLongitude();
new GetWeather().execute(Common.apiRequest(String.valueOf(lat), String.valueOf(lng)));
}
@Override
public void onStatusChanged(String provider, int status, Bundle extras) {
}
@Override
public void onProviderEnabled(String provider) {
}
@Override
public void onProviderDisabled(String provider) {
}
private class GetWeather extends AsyncTask<String, Void, String> {
ProgressDialog pd = new ProgressDialog(MainActivity.this);
@Override
protected void onPreExecute() {
super.onPreExecute();
pd.setTitle("Please wait...");
pd.show();
}
@Override
protected String doInBackground(String... params) {
String stream = null;
String urlString = params[0];
Helper http = new Helper();
stream = http.getHTTPData(urlString);
return stream;
}
@Override
protected void onPostExecute(String s) {
super.onPostExecute(s);
if(s.contains("Error: Not found city")){
pd.dismiss();
return;
}
Gson gson = new Gson();
Type mType = new TypeToken<OpenWeatherMap>(){}.getType();
openWeatherMap = gson.fromJson(s, mType);
pd.dismiss();
txtCity.setText(String.format("%s,%s",openWeatherMap.getName(),openWeatherMap.getSys().getCountry()));
txtLastUpdate.setText(String.format("Last Updated: %s", Common.getDateNow()));
txtDescription.setText(String.format("%s",openWeatherMap.getWeather().get(0).getDescription()));
txtHumidity.setText(String.format("%d%%",openWeatherMap.getMain().getHumidity()));
txtTime.setText(String.format("%s/%s",Common.unixTimeStampToDateTime(openWeatherMap.getSys().getSunrise()), Common.unixTimeStampToDateTime(openWeatherMap.getSys().getSunset())));
txtCelsius.setText(String.format("%.2f °C",openWeatherMap.getMain().getTemp()));
Picasso.with(MainActivity.this)
.load(Common.getImage(openWeatherMap.getWeather().get(0).getIcon()))
.into(imageView);
}
}
}
错误:
java.lang.NullPointerException:尝试在以下位置对空对象引用调用虚拟方法“boolean java.lang.String.containsjava.lang.CharSequence”
s为空,此处为:
s变量从doInBackground方法传递到onPostExecute,如下所示:
@Override
protected String doInBackground(String... params) {
String stream = null;
String urlString = params[0];
Helper http = new Helper();
stream = http.getHTTPData(urlString);
return stream;
}
这意味着流是空的
含义流=http.getHTTPDataurlString;无法以某种方式工作/返回null
@Override
protected String doInBackground(String... params) {
String stream = null;
String urlString = params[0];
Helper http = new Helper();
stream = http.getHTTPData(urlString);
return stream;
}