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我對Android比較陌生，我試圖按照this教程。Android數據下載實驗
我已經創建了下面的代碼一個小項目：
package com.example.revivaltimesv1;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.Reader;
import java.io.UnsupportedEncodingException;
import java.net.HttpURLConnection;
import java.net.URL;
import android.app.Activity;
import android.content.Context;
import android.net.ConnectivityManager;
import android.net.NetworkInfo;
import android.os.AsyncTask;
import android.os.Bundle;
import android.util.Log;
import android.view.Menu;
import android.widget.TextView;
import android.widget.Toast;
public class MainActivity extends Activity {
private static final int LENGTH_LONG = 10;
private TextView message;// = (TextView)findViewById(R.id.message);
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
message = (TextView)findViewById(R.id.message);
Log.i("mine", "TESTING ... TESTING!!!");
ConnectivityManager conManager = (ConnectivityManager)getSystemService(Context.CONNECTIVITY_SERVICE);
NetworkInfo networkInfo = conManager.getActiveNetworkInfo();
if(networkInfo != null && networkInfo.isConnected()){
Toast.makeText(this, "Established Network Connection!", LENGTH_LONG).show();
String stringURL = "http://178.79.128.76/GTK/node/7";
new DownloadStuff().execute(stringURL);
// new test().execute();
//message.setText("WORKING");
}else{
Toast.makeText(this, "No Network Connection!", LENGTH_LONG).show();
}
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.activity_main, menu);
return true;
}
//}
/* private class test extends AsyncTask<String, String, String>{
@Override
protected String doInBackground(String... params) {
// TODO Auto-generated method stub
return null;
}
}
*/
private class DownloadStuff extends AsyncTask<String, String, String>{
protected String doInBackground(String... url) {
// TODO Auto-generated method stub
Log.i("CHECK", "OUTSIDE");
try{
Log.i("CHECK", "SUCCESS: " + url[0]);
downloadUrl(url[0]);
Toast.makeText(getApplicationContext(), "WORKING !!!", LENGTH_LONG).show();
}catch(IOException i){
Log.i("CHECK", "NOT so successful");
Toast.makeText(getApplicationContext(), "ERROR: unable to establish contact with URL", LENGTH_LONG).show();
}
return null;
}
protected void onPostExecute(String result) {
// TODO Auto-generated method stub
// super.onPostExecute(result);
message.setText("Hurray!");
}
// Given a URL, establishes an HttpUrlConnection and retrieves
// the web page content as a InputStream, which it returns as
// a string.
private String downloadUrl(String myurl) throws IOException {
InputStream is = null;
// Only display the first 500 characters of the retrieved
// web page content.
int len = 500;
try {
URL url = new URL(myurl);
HttpURLConnection conn = (HttpURLConnection) url.openConnection();
conn.setReadTimeout(10000 /* milliseconds */);
conn.setConnectTimeout(15000 /* milliseconds */);
conn.setRequestMethod("GET");
conn.setDoInput(true);
// Starts the query
conn.connect();
int response = conn.getResponseCode();
Log.d("DEBUG_TAG", "The response is: " + response);
is = conn.getInputStream();
// Convert the InputStream into a string
String contentAsString = readIt(is, len);
return contentAsString;
// Makes sure that the InputStream is closed after the app is
// finished using it.
} finally {
if (is != null) {
is.close();
}
}
}
public String readIt(InputStream stream, int len) throws IOException, UnsupportedEncodingException {
Reader reader = null;
reader = new InputStreamReader(stream, "UTF-8");
char[] buffer = new char[len];
reader.read(buffer);
return new String(buffer);
}
}
}
該應用程序的工作原理簡單，但隨後崩潰給我下面的反饋：
02-08 03:39:16.316: E/AndroidRuntime(5106): FATAL EXCEPTION: AsyncTask #1
02-08 03:39:16.316: E/AndroidRuntime(5106): java.lang.RuntimeException: An error occured while executing doInBackground()
02-08 03:39:16.316: E/AndroidRuntime(5106): at android.os.AsyncTask$3.done(AsyncTask.java:200)
02-08 03:39:16.316: E/AndroidRuntime(5106): at java.util.concurrent.FutureTask$Sync.innerSetException(FutureTask.java:273)
02-08 03:39:16.316: E/AndroidRuntime(5106): at java.util.concurrent.FutureTask.setException(FutureTask.java:124)
02-08 03:39:16.316: E/AndroidRuntime(5106): at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:307)
02-08 03:39:16.316: E/AndroidRuntime(5106): at java.util.concurrent.FutureTask.run(FutureTask.java:137)
02-08 03:39:16.316: E/AndroidRuntime(5106): at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1068)
02-08 03:39:16.316: E/AndroidRuntime(5106): at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:561)
02-08 03:39:16.316: E/AndroidRuntime(5106): at java.lang.Thread.run(Thread.java:1102)
02-08 03:39:16.316: E/AndroidRuntime(5106): Caused by: java.lang.RuntimeException: Can't create handler inside thread that has not called Looper.prepare()
02-08 03:39:16.316: E/AndroidRuntime(5106): at android.os.Handler.<init>(Handler.java:121)
02-08 03:39:16.316: E/AndroidRuntime(5106): at android.widget.Toast.<init>(Toast.java:68)
02-08 03:39:16.316: E/AndroidRuntime(5106): at android.widget.Toast.makeText(Toast.java:231)
02-08 03:39:16.316: E/AndroidRuntime(5106): at com.example.revivaltimesv1.MainActivity$DownloadStuff.doInBackground(MainActivity.java:74)
02-08 03:39:16.316: E/AndroidRuntime(5106): at com.example.revivaltimesv1.MainActivity$DownloadStuff.doInBackground(MainActivity.java:1)
02-08 03:39:16.316: E/AndroidRuntime(5106): at android.os.AsyncTask$2.call(AsyncTask.java:185)
02-08 03:39:16.316: E/AndroidRuntime(5106): at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:305)
02-08 03:39:16.316: E/AndroidRuntime(5106): ... 4 more
我看遍至的底部錯誤堆棧，但... 4更多似乎隱藏與我的代碼相關的部分 - 我認爲。