![](/img/trans.png)
[英]Android app working on emulator but not real device, SharePreferences
[英]Android app crashing on real device but working on emulator
我对编程有点陌生,并且尝试制作一个项目女巫是 android 应用程序,但是当我尝试在我的设备上运行它时它只是崩溃了。
我在我的 logcat 中收到这些错误:
java.lang.NullPointerException: Attempt to get length of null array
2020-07-12 19:52:04.128 12417-12417/? E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.temperatura, PID: 12417
java.lang.NullPointerException: Attempt to invoke virtual method 'int java.lang.String.length()' on a null object reference
at org.json.JSONTokener.nextCleanInternal(JSONTokener.java:121)
at org.json.JSONTokener.nextValue(JSONTokener.java:98)
at org.json.JSONArray.<init>(JSONArray.java:94)
at org.json.JSONArray.<init>(JSONArray.java:110)
at com.example.temperatura.MainActivity.loadIntoListView(MainActivity.java:116)
at com.example.temperatura.MainActivity.access$200(MainActivity.java:21)
at com.example.temperatura.MainActivity$1DownloadJSON.onPostExecute(MainActivity.java:68)
at com.example.temperatura.MainActivity$1DownloadJSON.onPostExecute(MainActivity.java:52)
at android.os.AsyncTask.finish(AsyncTask.java:755)
at android.os.AsyncTask.access$900(AsyncTask.java:192)
at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:772)
at android.os.Handler.dispatchMessage(Handler.java:107)
at android.os.Looper.loop(Looper.java:224)
at android.app.ActivityThread.main(ActivityThread.java:7520)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:539)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:950)
这是我的主要活动。java:
package com.example.temperatura;
import android.os.AsyncTask;
import android.os.Bundle;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import android.widget.Toast;
import androidx.appcompat.app.AppCompatActivity;
import androidx.swiperefreshlayout.widget.SwipeRefreshLayout;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;
import java.util.ArrayList;
import java.util.List;
public class MainActivity extends AppCompatActivity {
ListView listView;
List<String> sensor = new ArrayList<>();
ArrayAdapter arrayAdapter;
boolean needRefresh; // whether refresh is needed
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
final SwipeRefreshLayout pullToRefresh = findViewById(R.id.pullToRefresh);
listView = (ListView) findViewById(R.id.listView);
downloadJSON("http://pillsmanager.com/temperatura/conn_app.php");
pullToRefresh.setOnRefreshListener(new SwipeRefreshLayout.OnRefreshListener() {
@Override
public void onRefresh() {
downloadJSON("http://pillsmanager.com/temperatura/conn_app.php");
pullToRefresh.setRefreshing(false);
needRefresh = true;
}
});
}
private void downloadJSON(final String urlWebService) {
class DownloadJSON extends AsyncTask<Void, Void, String> {
@Override
protected void onPreExecute() {
super.onPreExecute();
}
@Override
protected void onPostExecute(String s) {
super.onPostExecute(s);
Toast.makeText(getApplicationContext(), s, Toast.LENGTH_SHORT).show();
try {
if (needRefresh) {
updateAndLoadIntoListView(s);
} else {
loadIntoListView(s);
}
} catch (JSONException e) {
e.printStackTrace();
}
}
@Override
protected String doInBackground(Void... voids) {
try {
URL url = new URL(urlWebService);
HttpURLConnection con = (HttpURLConnection) url.openConnection();
StringBuilder sb = new StringBuilder();
BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(con.getInputStream()));
String json;
while ((json = bufferedReader.readLine()) != null) {
sb.append(json + "\n");
}
return sb.toString().trim();
} catch (Exception e) {
return null;
}
}
}
DownloadJSON getJSON = new DownloadJSON();
getJSON.execute();
}
private void updateAndLoadIntoListView(String json) throws JSONException {
JSONArray jsonArray = new JSONArray(json);
sensor.clear();
for (int i = 0; i < jsonArray.length(); i++) {
final JSONObject obj = jsonArray.getJSONObject(i);
sensor.add(obj.getString("temperature") + " " + obj.getString("humidity"));
}
arrayAdapter.notifyDataSetChanged();
needRefresh = false;
}
private void loadIntoListView(String json) throws JSONException {
JSONArray jsonArray = new JSONArray(json);
for (int i = 0; i < jsonArray.length(); i++) {
final JSONObject obj = jsonArray.getJSONObject(i);
sensor.add(obj.getString("temperature") + " " + obj.getString("humidity"));
}
arrayAdapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, sensor);
listView.setAdapter(arrayAdapter);
}
}
非常感谢所有帮助,我已经尝试了所有方法,但我无法找出问题所在
从堆栈跟踪来看,您似乎正在将null
传递给loadIntoListView
方法。
只有当您处理下载的doInBackground
方法遇到异常时,它才会发生在您的代码中。
它在设备上失败并在模拟器上工作的原因可能有很多。 我建议切换到一些网络库来处理下载和处理那些边缘情况。 这真的很烦人。 尝试使用OkHttp
声明:本站的技术帖子网页,遵循CC BY-SA 4.0协议,如果您需要转载,请注明本站网址或者原文地址。任何问题请咨询:yoyou2525@163.com.