我制作了一个 Android 登录应用程序，用于验证 mysql 数据库中的用户名和密码，如果它们匹配，则打开另一个 Activity 。当设备连接到互联网时，该应用程序运行正常，但当在没有网络连接的情况下打开该应用程序时，它会意外关闭。任何帮助，将不胜感激。不幸的是我是在 AIDE 中开发的，无法发布 logcat。
MainActivity.java
MainActivity.java
package com.mycompany.dynamic;
import java.util.ArrayList;
import java.util.List;
import org.apache.http.NameValuePair;
import org.apache.http.message.BasicNameValuePair;
import org.json.JSONException;
import org.json.JSONObject;
import android.app.Activity;
import android.app.ProgressDialog;
import android.content.Intent;
import android.os.AsyncTask;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;
import android.widget.*;
import android.graphics.*;
public class MainActivity extends Activity implements OnClickListener{
private EditText user, pass;
private Button bLogin;
// Progress Dialog
private ProgressDialog pDialog;
// JSON parser class
JSONParser jsonParser = new JSONParser();
private static final String LOGIN_URL = "http://necrecords.16mb.com/login.php";
private static final String TAG_SUCCESS = "success";
private static final String TAG_MESSAGE = "message";
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
user = (EditText)findViewById(R.id.username);
pass = (EditText)findViewById(R.id.password);
bLogin = (Button)findViewById(R.id.login);
TextView tx1 = (TextView)findViewById(R.id.welcometv);
Typeface custom_font1 = Typeface.createFromAsset(getAssets(), "fonts/myfont1.otf");
tx1.setTypeface(custom_font1);
TextView tx2 = (TextView)findViewById(R.id.welcometexttv);
Typeface custom_font2 = Typeface.createFromAsset(getAssets(), "fonts/myfont2.ttf");
tx2.setTypeface(custom_font2);
bLogin.setOnClickListener(this);
}
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
switch (v.getId()) {
case R.id.login:
new AttemptLogin().execute();
// here we have used, switch case, because on login activity you may //also want to show registration button, so if the user is new ! we can go the //registration activity , other than this we could also do this without switch //case.
default:
break;
}
}
class AttemptLogin extends AsyncTask<String, String, String> {
/**
* Before starting background thread Show Progress Dialog
* */
boolean failure = false;
@Override
protected void onPreExecute() {
super.onPreExecute();
pDialog = new ProgressDialog(MainActivity.this);
pDialog.setMessage("Attempting for login...");
pDialog.setIndeterminate(false);
pDialog.setCancelable(true);
pDialog.show();
}
@Override
protected String doInBackground(String... args) {
// TODO Auto-generated method stub
// here Check for success tag
int success;
String username = user.getText().toString();
String password = pass.getText().toString();
try {
List<NameValuePair> params = new ArrayList<NameValuePair>();
params.add(new BasicNameValuePair("username", username));
params.add(new BasicNameValuePair("password", password));
Log.d("request!", "starting");
JSONObject json = jsonParser.makeHttpRequest(
LOGIN_URL, "POST", params);
// checking log for json response
Log.d("Login attempt", json.toString());
// success tag for json
success = json.getInt(TAG_SUCCESS);
if (success == 1) {
Log.d("Successfully Login!", json.toString());
Intent ii = new Intent(MainActivity.this,MainMenu.class);
finish();
// this finish() method is used to tell android os that we are done with current //activity now! Moving to other activity
startActivity(ii);
return json.getString(TAG_MESSAGE);
}else{
return json.getString(TAG_MESSAGE);
}
} catch (JSONException e) {
e.printStackTrace();
}
return null;
}
/**
* Once the background process is done we need to Dismiss the progress dialog asap
* **/
protected void onPostExecute(String message) {
pDialog.dismiss();
if (message != null){
Toast.makeText(MainActivity.this, message, Toast.LENGTH_LONG).show();
}
}
}
}
JSONParser.java
JSONParser.java
package com.mycompany.dynamic;
import org.apache.http.HttpEntity;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import org.apache.http.HttpResponse;
import java.io.InputStreamReader;
import java.io.UnsupportedEncodingException;
import java.util.List;
import org.apache.http.NameValuePair;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.entity.UrlEncodedFormEntity;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.client.utils.URLEncodedUtils;
import org.apache.http.impl.client.DefaultHttpClient;
import org.json.JSONException;
import org.json.JSONObject;
import android.util.Log;
public class JSONParser {
static InputStream is = null;
static JSONObject jsonObj ;
static String json = "";
// default no argument constructor for jsonpaser class
public JSONParser() {
}
public JSONObject getJSONFromUrl(final String url) {
// Making HTTP request
try {
DefaultHttpClient httpClient = new DefaultHttpClient();
HttpPost httpPost = new HttpPost(url);
// Executing POST request & storing the response from server locally.
HttpResponse httpResponse = httpClient.execute(httpPost);
HttpEntity httpEntity = httpResponse.getEntity();
is = httpEntity.getContent();
} catch (UnsupportedEncodingException e) {
e.printStackTrace();
} catch (ClientProtocolException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
try {
// Create a BufferedReader
BufferedReader reader = new BufferedReader(new InputStreamReader(
is, "iso-8859-1"), 8);
// Declaring string builder
StringBuilder str = new StringBuilder();
// string to store the JSON object.
String strLine = null;
// Building while we have string !equal null.
while ((strLine = reader.readLine()) != null) {
str.append(strLine + "\n");
}
// Close inputstream.
is.close();
// string builder data conversion to string.
json = str.toString();
} catch (Exception e) {
Log.e("Error", " something wrong with converting result " + e.toString());
}
// Try block used for pasrseing String to a json object
try {
jsonObj = new JSONObject(json);
} catch (JSONException e) {
Log.e("json Parsering", "" + e.toString());
}
// Returning json Object.
return jsonObj;
}
public JSONObject makeHttpRequest(String url, String method,
List<NameValuePair> params) {
// Make HTTP request
try {
// checking request method
if(method == "POST"){
// now defaultHttpClient object
DefaultHttpClient httpClient = new DefaultHttpClient();
HttpPost httpPost = new HttpPost(url);
httpPost.setEntity(new UrlEncodedFormEntity(params));
HttpResponse httpResponse = httpClient.execute(httpPost);
HttpEntity httpEntity = httpResponse.getEntity();
is = httpEntity.getContent();
}else if(method == "GET"){
// request method is GET
DefaultHttpClient httpClient = new DefaultHttpClient();
String paramString = URLEncodedUtils.format(params, "utf-8");
url += "?" + paramString;
HttpGet httpGet = new HttpGet(url);
HttpResponse httpResponse = httpClient.execute(httpGet);
HttpEntity httpEntity = httpResponse.getEntity();
is = httpEntity.getContent();
}
} catch (UnsupportedEncodingException e) {
e.printStackTrace();
} catch (ClientProtocolException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
try {
BufferedReader reader = new BufferedReader(new InputStreamReader(
is, "iso-8859-1"), 8);
StringBuilder str = new StringBuilder();
String strLine = null;
while ((strLine = reader.readLine()) != null) {
str.append(strLine + "\n");
}
is.close();
json = str.toString();
} catch (Exception e) {
}
// now will try to parse the string into JSON object
try {
jsonObj = new JSONObject(json);
} catch (JSONException e) {
}
return jsonObj;
}
}
最佳答案
在调用服务器之前确保网络正常工作
if(isNetworkAvailable){
new AttemptLogin().execute();
}
当没有收到数据时，json解析器无法解析数据并抛出异常。 网络可用性的方法可能是
public boolean isNetworkAvailable(Context context) {
// TODO Auto-generated method stub
boolean haveConnectedWifi = false;
boolean haveConnectedMobile = false;
ConnectivityManager cm = (ConnectivityManager) context.getSystemService(Context.CONNECTIVITY_SERVICE);
NetworkInfo[] netInfo = cm.getAllNetworkInfo();
for (NetworkInfo ni : netInfo) {
if (ni.getTypeName().equalsIgnoreCase("WIFI"))
if (ni.isConnected())
haveConnectedWifi = true;
if (ni.getTypeName().equalsIgnoreCase("MOBILE"))
if (ni.isConnected())
haveConnectedMobile = true;
}
return haveConnectedWifi || haveConnectedMobile;
}
关于android - 应用程序在没有网络连接的情况下意外关闭，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/27889850/