我已经使用了AsyncTask，但我不明白为什么我在设备上测试时仍会出现错误（OS 4.0）。我的apk版本在2.3.3中。我想我的代码错了，但我不知道我的错误在哪里。有人请帮助我，非常感谢
login.java
package com.karismaelearning;
public class Login extends Activity {
public Koneksi linkurl;
String SERVER_URL;
private Button login, register, setting;
private EditText username, password;
public ProgressDialog progressDialog;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.login);
setting = (Button)findViewById(R.id.bsetting);
login = (Button) findViewById(R.id.login);
register = (Button) findViewById(R.id.reg);
username = (EditText) findViewById(R.id.uname);
password = (EditText) findViewById(R.id.pass);
setting.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
Intent intentSet = new Intent(Login.this, UrlSetting.class);
startActivity(intentSet);
}
});
register.setOnClickListener(new OnClickListener() {
public void onClick(View v) {
Intent intentReg = new Intent(Login.this, Register.class);
startActivity(intentReg);
}
});
login.setOnClickListener(new OnClickListener() {
public void onClick(View v) {
new LoginTask().execute();
}
});
}
protected String tryLogin(String mUsername, String mPassword){
Log.d(" TryLoginCheck ","Here");
HttpURLConnection connection;
OutputStreamWriter request = null;
URL url = null;
String response = null;
String temp=null;
String parameters = "username="+mUsername+"&password="+mPassword;
System.out.println("UserName"+mUsername+"\n"+"password"+mPassword);
Log.d("Parameters",parameters);
try{
linkurl = new Koneksi(this);
SERVER_URL = linkurl.getUrl();
SERVER_URL += "/mobile/Login.php";
url = new URL(SERVER_URL);
connection = (HttpURLConnection) url.openConnection();
connection.setDoOutput(true);
connection.setRequestProperty("Content-Type", "application/x-www-form-urlencoded");
connection.setRequestMethod("POST");
request = new OutputStreamWriter(connection.getOutputStream());
request.write(parameters);
request.flush();
request.close();
String line = "";
InputStreamReader isr = new InputStreamReader(connection.getInputStream());
BufferedReader reader = new BufferedReader(isr);
StringBuilder sb = new StringBuilder();
while ((line = reader.readLine()) != null) {
sb.append(line + "\n");
}
temp=sb.toString();
Log.d("Temp",temp);
response = sb.toString();
Log.d("Response",response);
Log.d("Sb Value",sb.toString());
isr.close();
reader.close();
}
catch(IOException e) {
Toast.makeText(this,e.toString(),Toast.LENGTH_SHORT).show();
}
return response;
}
public class LoginTask extends AsyncTask<String, String, String> {
String response = null;
@Override
protected void onPreExecute()
{
}
@Override
protected String doInBackground(String... arg0)
{
String mUsername = username.getText().toString();
String mPassword = password.getText().toString();
response = tryLogin(mUsername, mPassword).trim();
return response;
}
protected void onPostExecute(String result){
if(result==null)
{
Toast.makeText(Login.this,"result is null- an error occured",Toast.LENGTH_SHORT).show();
}
else{
Log.d("Check","Here");
Log.d("Response",response);
if(response.toLowerCase().contains("berhasil"))
{
String nama = username.getText().toString();
Intent newIntent = new Intent(Login.this, MainPage.class);
Bundle bundle = new Bundle();
bundle.putString("nama", nama);
newIntent.putExtras(bundle);
startActivityForResult(newIntent, 0);
}
else
{
//Optional
//Kalau bisa dibuat constant untuk menghindari salah penulisan
String RoleError = "ROLE SALAH";
String UserError = "USER SALAH";
createDialog("Maaf", response.equals(RoleError) ? "Role Anda bukan Student!" : "Username Atau Password Salah!");
}
}
}
}
private void createDialog(String title, String text) {
AlertDialog ad = new AlertDialog.Builder(this)
.setPositiveButton("Ok", null)
.setTitle(title)
.setMessage(text)
.create();
ad.show();
}
}
logcat的
06-10 16:50:00.082: D/TryLoginCheck(4534): Here
06-10 16:50:00.090: I/System.out(4534): UserName
06-10 16:50:00.090: I/System.out(4534): password
06-10 16:50:00.090: D/Parameters(4534): username=&password=
06-10 16:50:00.122: W/dalvikvm(4534): threadid=11: thread exiting with uncaught exception (group=0x40bd31f8)
06-10 16:50:00.129: E/AndroidRuntime(4534): FATAL EXCEPTION: AsyncTask #1
06-10 16:50:00.129: E/AndroidRuntime(4534): java.lang.RuntimeException: An error occured while executing doInBackground()
06-10 16:50:00.129: E/AndroidRuntime(4534): at android.os.AsyncTask$3.done(AsyncTask.java:278)
06-10 16:50:00.129: E/AndroidRuntime(4534): at java.util.concurrent.FutureTask$Sync.innerSetException(FutureTask.java:273)
06-10 16:50:00.129: E/AndroidRuntime(4534): at java.util.concurrent.FutureTask.setException(FutureTask.java:124)
06-10 16:50:00.129: E/AndroidRuntime(4534): at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:307)
06-10 16:50:00.129: E/AndroidRuntime(4534): at java.util.concurrent.FutureTask.run(FutureTask.java:137)
06-10 16:50:00.129: E/AndroidRuntime(4534): at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:208)
06-10 16:50:00.129: E/AndroidRuntime(4534): at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1076)
06-10 16:50:00.129: E/AndroidRuntime(4534): at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:569)
06-10 16:50:00.129: E/AndroidRuntime(4534): at java.lang.Thread.run(Thread.java:856)
06-10 16:50:00.129: E/AndroidRuntime(4534): Caused by: java.lang.NullPointerException
06-10 16:50:00.129: E/AndroidRuntime(4534): at com.karismaelearning.Login$LoginTask.doInBackground(Login.java:151)
06-10 16:50:00.129: E/AndroidRuntime(4534): at com.karismaelearning.Login$LoginTask.doInBackground(Login.java:1)
06-10 16:50:00.129: E/AndroidRuntime(4534): at android.os.AsyncTask$2.call(AsyncTask.java:264)
06-10 16:50:00.129: E/AndroidRuntime(4534): at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:305)
06-10 16:50:00.129: E/AndroidRuntime(4534): ... 5 more
06-10 16:50:05.192: D/OpenGLRenderer(4534): Flushing caches (mode 0)
06-10 16:50:06.309: D/OpenGLRenderer(4534): Flushing caches (mode 1)
06-10 16:50:07.536: I/Process(4534): Sending signal. PID: 4534 SIG: 9
答案 0 :(得分：5)
在tryLogin中，当发生异常时，你会这样做：
Toast.makeText(this,e.toString(),Toast.LENGTH_SHORT).show();
那是错的。 Toast.show()必须在UI线程上运行。
in
tryLogin() {
try {
} catch(IOException e) {
return null;
}
}
并在
protected void onPostExecute(String result){
if (result == null) {
Toast.makeText(Login.this,"result is null- an error occured"),Toast.LENGTH_SHORT).show();
} else {
result = result.trim();
// the other stuff
}
}
@Override
protected String doInBackground(String... arg0)
{
String mUsername = username.getText().toString();
String mPassword = password.getText().toString();
return tryLogin(mUsername, mPassword);
}
答案 1 :(得分：1)
要弄清楚为什么例程tryLogin不起作用，我建议遵循@ BlackBelt的建议，除了tryLogin（）使用：
tryLogin() {
try {
} catch(Throwable e) {
e.printStackTrace();
Log.d("Error",e.getMessage());
return null;
}
}
并查看生成的错误消息。
答案 2 :(得分：0)
登录请求放在doInBackground（）方法中。并处理AsyncTask的onPostExecute（）方法中的响应
答案 3 :(得分：0)
Toast无法在catch中运行，因为后台线程无法访问用户界面。但是，onPostExecute确实在主线程上运行，因此它可以访问用户界面，toast可以在那里工作。
所以我定义了一个新类来保存AsyncTask的结果，并设置它以便该类可以表示成功或错误消息。然后让onPostExecute相应地运行，具体取决于是否发生错误。
答案 4 :(得分：0)
如果我理解正确，错误是由于 Looper.prepare（）未被手动调用或自动从框架调用。 的的
尝试在
super()的构造函数中调用
LoginTask（根据我的理解，当您扩展AsyncTask并从UI线程执行/启动它时，您将不会得到此异常，因为Looper将由超类自动准备。）
或。快速修复（不推荐）：在doInBackground中调用Looper.prepare（）
@Override
protected String doInBackground(String... arg0) {
try {
Looper.prepare();
} catch (Exception e){
// ignore. There can be only one Looper associated with thread
// This happens when the current thread already has Looper associated with it
}
//TODO: Your original content of doInBackground(...)
}
P.S。如果您通过扩展线程而不是准备 Looper 并使用UI元素的上下文来创建自定义线程（例如，To to Toast消息），Android将抛出Looper未准备好的异常！ / p>