请引用下面的代码,不断调用一个新的AsyncTask
。 AsyncTask
的用途是发出 HTTP 请求,并更新字符串 result
。
package room.temperature;
import java.io.BufferedReader;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.concurrent.ExecutionException;
import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.NameValuePair;
import org.apache.http.client.HttpClient;
import org.apache.http.client.entity.UrlEncodedFormEntity;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.impl.client.DefaultHttpClient;
import android.app.Activity;
import android.os.AsyncTask;
import android.os.Bundle;
import android.util.Log;
import android.widget.TextView;
public class RoomTemperatureActivity extends Activity {
String result = null;
StringBuilder sb=null;
TextView TemperatureText, DateText;
ArrayList<NameValuePair> nameValuePairs;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
TemperatureText = (TextView) findViewById(R.id.temperature);
DateText = (TextView) findViewById(R.id.date);
nameValuePairs = new ArrayList<NameValuePair>();
for (int i = 0; i < 10; i++) {
RefreshValuesTask task = new RefreshValuesTask();
task.execute("");
}
}
// The definition of our task class
private class RefreshValuesTask extends AsyncTask<String, Integer, String> {
@Override
protected void onPreExecute() {
super.onPreExecute();
}
@Override
protected String doInBackground(String... params) {
InputStream is = null;
try {
HttpClient httpclient = new DefaultHttpClient();
HttpPost httppost = new HttpPost("http://mywebsite.com/roomtemp/tempscript.php");
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());
}
try {
BufferedReader reader = new BufferedReader(new InputStreamReader(is,"iso-8859-1"),8);
sb = new StringBuilder();
sb.append(reader.readLine());
is.close();
result=sb.toString();
}
catch(Exception e) {
Log.e("log_tag", "Error converting result " + e.toString());
}
return result;
}
@Override
protected void onProgressUpdate(Integer... values) {
super.onProgressUpdate(values);
}
@Override
protected void onPostExecute(String result) {
super.onPostExecute(result);
//System.out.println(result);
setValues(result);
}
}
public void setValues(String resultValue) {
System.out.println(resultValue);
String[] values = resultValue.split("&");
TemperatureText.setText(values[0]);
DateText.setText(values[1]);
}
}
我遇到的问题在某种程度上与AsyncTask
或函数setValues()
有关,但我不确定如何。本质上,我希望每次调用 AsyncTask
都能运行,最终在无限的 while 循环中运行,并更新 TextView
字段,就像我在 setValues
中尝试的那样>。我从昨天开始就尝试过询问question由此产生了这段代码,供引用。
哦,是的,我确实尝试使用 AsyncTask
get()
方法,但这也不起作用,因为我发现它实际上是一个同步调用,并使 AsyncTask
的全部意义变得无用。
最佳答案
使用 publishProgress()
和 onProgressUpdate()
方法来发布进度,同时在 doInBackground()
方法中执行某些任务。
因此将您的代码更改为以下内容:
package room.temperature;
import java.io.BufferedReader;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.concurrent.ExecutionException;
import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.NameValuePair;
import org.apache.http.client.HttpClient;
import org.apache.http.client.entity.UrlEncodedFormEntity;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.impl.client.DefaultHttpClient;
import android.app.Activity;
import android.os.AsyncTask;
import android.os.Bundle;
import android.util.Log;
import android.widget.TextView;
public class RoomTemperatureActivity extends Activity {
String result = null;
StringBuilder sb=null;
TextView TemperatureText, DateText;
ArrayList<NameValuePair> nameValuePairs;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
TemperatureText = (TextView) findViewById(R.id.temperature);
DateText = (TextView) findViewById(R.id.date);
nameValuePairs = new ArrayList<NameValuePair>();
RefreshValuesTask task = new RefreshValuesTask();
task.execute("");
}
// The definition of our task class
private class RefreshValuesTask extends AsyncTask<String, Integer, String> {
@Override
protected void onPreExecute() {
super.onPreExecute();
}
@Override
protected String doInBackground(String... params) {
InputStream is = null;
for (int i = 0; i < 10; i++) {
try {
HttpClient httpclient = new DefaultHttpClient();
HttpPost httppost = new HttpPost("http://mywebsite.com/roomtemp/tempscript.php");
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());
}
try {
BufferedReader reader = new BufferedReader(new InputStreamReader(is,"iso-8859-1"),8);
sb = new StringBuilder();
sb.append(reader.readLine());
is.close();
result=sb.toString();
publishProgress(result);
}
catch(Exception e) {
Log.e("log_tag", "Error converting result " + e.toString());
}
}
return result;
}
@Override
protected void onProgressUpdate(String... values) {
super.onProgressUpdate(values);
setValues(values);
}
@Override
protected void onPostExecute(String result) {
super.onPostExecute(result);
//System.out.println(result);
setValues(result);
}
}
public void setValues(String resultValue) {
System.out.println(resultValue);
String[] values = resultValue.split("&");
TemperatureText.setText(values[0]);
DateText.setText(values[1]);
}
}
关于java - 使用 AsyncTask,但遇到意外行为,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/13097156/