我在下面使用此代码，它在 Android 2.3.3 中完美运行。但是，在 4.0+ 中，它无法以某种方式连接到数据库。我看到一些关于你需要在异步课程中获得它的帖子。我也试过了，但我似乎无法正常工作。我可能用错了，但我很难理解。
public class connector extends Activity {
/** Called when the activity is first created. */
TextView txt;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
getServerData(null);
}
//i use my real ip here
public String getServerData(String returnString) {
System.out.println("going to connector class");
InputStream is = null;
final String KEY_121 = "http://10.0.0.128/connector.php";
String result = "";
//the year data to send
// ArrayList<NameValuePair> nameValuePairs = new ArrayList<NameValuePair>();
// nameValuePairs.add(new BasicNameValuePair("year","1970"));
//http post
try{
HttpClient httpclient = new DefaultHttpClient();
HttpPost httppost = new HttpPost(KEY_121);
// httppost.setEntity(new UrlEncodedFormEntity(nameValuePairs));
HttpResponse response = httpclient.execute(httppost);
HttpEntity entity = response.getEntity();
is = entity.getContent();
}catch(Exception e){
Log.e("log_tag", "Error in http connection "+e.toString());
}
//convert response to string
try{
BufferedReader reader = new BufferedReader(new InputStreamReader(is,"iso-8859-1"),8);
StringBuilder sb = new StringBuilder();
String line = null;
while ((line = reader.readLine()) != null) {
sb.append(line + "\n");
}
is.close();
result=sb.toString();
}catch(Exception e){
Log.e("log_tag", "Error converting result "+e.toString());
}
//parse json data
try{
JSONArray jArray = new JSONArray(result);
for(int i=0;i<jArray.length();i++){
JSONObject json_data = jArray.getJSONObject(i);
Log.i("log_tag","ID: "+json_data.getInt("ID")+
", \nActara: "+json_data.getString("Actara")
);
//Get an output to the screen
returnString += "\n\t" + jArray.getJSONObject(i);
}
}catch(JSONException e){
Log.e("log_tag", "Error parsing data "+e.toString());
}
return returnString;
}
}
Logcat 错误（在 4.0+ 上）：
11-12 12:02:35.658: E/log_tag(14083): Error in http connection android.os.NetworkOnMainThreadException
11-12 12:02:35.658: E/log_tag(14083): Error converting result java.lang.NullPointerException
11-12 12:02:35.663: E/log_tag(14083): Error parsing data org.json.JSONException: End of input at character 0 of
只有第一个错误行很重要，因为它无法连接到数据库，它给出了一个 nullPointer（第二个和第三个错误）。
这是我在异步中尝试过的：
public class connector extends Activity {
/** Called when the activity is first created. */
TextView txt;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
new BackgroundAsyncTask().execute();
}
public class BackgroundAsyncTask extends
AsyncTask<Void, Integer, Void> {
InputStream is = null;
final String KEY_121 = "http://10.0.0.128/connector.php";
String result = "";
String returnString = "";
protected void onPostExecute(Void result) {
}
@Override
protected void onPreExecute() {
System.out.println("onPreExecute");
}
protected Void doInBackground(String... params) {
try{
System.out.println("background in progress");
HttpClient httpclient = new DefaultHttpClient();
HttpPost httppost = new HttpPost(KEY_121);
// httppost.setEntity(new UrlEncodedFormEntity(nameValuePairs));
HttpResponse response = httpclient.execute(httppost);
HttpEntity entity = response.getEntity();
is = entity.getContent();
}catch(Exception e){
Log.e("log_tag", "Error in http connection "+e.toString());
}
//convert response to string
try{
BufferedReader reader = new BufferedReader(new InputStreamReader(is,"iso-8859-1"),8);
StringBuilder sb = new StringBuilder();
String line = null;
while ((line = reader.readLine()) != null) {
sb.append(line + "\n");
}
is.close();
result=sb.toString();
}catch(Exception e){
Log.e("log_tag", "Error converting result "+e.toString());
}
//parse json data
try{
JSONArray jArray = new JSONArray(result);
for(int i=0;i<jArray.length();i++){
JSONObject json_data = jArray.getJSONObject(i);
Log.i("log_tag","ID: "+json_data.getInt("ID")+
", \nActara: "+json_data.getString("Actara")
);
//Get an output to the screen
returnString += "\n\t" + jArray.getJSONObject(i);
}
}catch(JSONException e){
Log.e("log_tag", "Error parsing data "+e.toString());
}
return null;
}
protected void onProgressUpdate(Integer... values) {
}
@Override
protected Void doInBackground(Void... params) {
// TODO Auto-generated method stub
return null;
}
}
}
有人可以帮助我吗？我不确定真正的原因是为什么它不适用于 4.0+。
如果您需要更多信息，请说出来，我会发布。
代码可能有点乱，我还没有真正“清理”它。