我在执行 postexecute() 上的 AlertDialog 时遇到问题。抛出这个异常 Caused by: java.lang.RuntimeException: 无法在未调用 Looper.prepare() 的线程内创建处理程序 或者，当我放入 AlertDialog.Builder 时，它只是不起作用 请帮助。 同样在输入错误密码的情况下，该过程终止。在用户名或密码无效的情况下如何调用 Toast 方法 下面是代码 fragment
public void Login() {
// Toast.makeText(getBaseContext(), pass.getText() + " "
// +user.getText(),
// Toast.LENGTH_SHORT).show();
String url = "http://107.20.195.151/mcast_ws/" + "?user="
+ user.getText().toString() + "&password="
+ pass.getText().toString();
result = getHttpResponse(url);
}
String result;
private String getHttpResponse(String location) {
result = "";
URL url = null;
Log.d(LOGTAG, " " + "location " + location);
try {
url = new URL(location);
} catch (MalformedURLException e) {
Log.e(LOGTAG, " " + "error" + e.getMessage());
}
if (url != null) {
try {
HttpURLConnection connection = (HttpURLConnection) url
.openConnection();
BufferedReader in = new BufferedReader(new InputStreamReader(
connection.getInputStream()));
String inputLine;
int lineCount = 0;
while ((inputLine = in.readLine()) != null) {
result += inputLine.trim();
}
in.close();
connection.disconnect();
} catch (Exception e) {
Log.e(LOGTAG, " " + "IOError " + e.getMessage());
Toast.makeText(getBaseContext(), "No Internet Access",
Toast.LENGTH_SHORT);
}
} else {
Log.e(LOGTAG, " " + "url" + url);
}
return result;
}
class PostToTwitter extends AsyncTask<String, Void, String> {
@Override
protected String doInBackground(String... params) {
Login();
Log.d(LOGTAG, "Success");
Log.d(LOGTAG, result);
Log.d(LOGTAG, result.substring(0, 16).trim());
// Log.d(TweetActivity.getLogtag(),"Successfully Posted: " +
// params[0]);
return "success";
}
@Override
protected void onPostExecute(String r) {
// TODO Auto-generated method stub
super.onPostExecute(result);
String msg = "Login successful";
if (result.substring(0, 16).trim().equals(msg)) {
// System.out.println(result.substring(0, 16).trim());
Log.d(LOGTAG, " " + "Connection Test" + result);
AlertDialog.Builder builder = new AlertDialog.Builder(getApplicationContext());
builder.setMessage("Are you sure send this SMS?")
.setCancelable(false)
.setPositiveButton("Yes", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int id) {
//...Attach another thread event to send the sms
}
})
.setNegativeButton("No", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int id) {
dialog.cancel();
}
});
Log.e(LOGTAG, "Error detected 2");
AlertDialog alert = builder.create();
alert.show();
//return "success";
// Toast.makeText(getBaseContext(),
// "Login Succesful",Toast.LENGTH_SHORT).show();
} else {
Toast.makeText(getBaseContext(),
"Login UnSuccesful. Check Username or password",
Toast.LENGTH_SHORT).show();
//return null;
}
// Toast.makeText(getApplicationContext(), result
// ,Toast.LENGTH_SHORT).show();
Log.e(LOGTAG, "Error detected");
/*
Intent i = new Intent("com.sms.subsahara.COMPOSESMS");
startActivity(i);
//Log.e(LOGTAG, " " + "error2");*/
}
}
根据Alex的建议，我修改了上面的原始代码，但仍然报错。下面是logcat的异常
E/AndroidRuntime( 326): Uncaught handler: thread main exiting due to uncaught exception
E/AndroidRuntime( 326): android.view.WindowManager$BadTokenException: Unable to add window -- token null is not for an application
E/AndroidRuntime( 326): at android.view.ViewRoot.setView(ViewRoot.java:472)
E/AndroidRuntime( 326): at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:177)
E/AndroidRuntime( 326): at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:91)
E/AndroidRuntime( 326): at android.app.Dialog.show(Dialog.java:239)
E/AndroidRuntime( 326): at com.sms.subsahara.WebMessengerActivity$PostToTwitter.onPostExecute(WebMessengerActivity.java:216)
E/AndroidRuntime( 326): at com.sms.subsahara.WebMessengerActivity$PostToTwitter.onPostExecute(WebMessengerActivity.java:1)
E/AndroidRuntime( 326): at android.os.AsyncTask.finish(AsyncTask.java:417)
E/AndroidRuntime( 326): at android.os.AsyncTask.access$300(AsyncTask.java:127)
E/AndroidRuntime( 326): at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:429)
E/AndroidRuntime( 326): at android.os.Handler.dispatchMessage(Handler.java:99)
E/AndroidRuntime( 326): at android.os.Looper.loop(Looper.java:123)
E/AndroidRuntime( 326): at android.app.ActivityThread.main(ActivityThread.java:4363)
E/AndroidRuntime( 326): at java.lang.reflect.Method.invokeNative(Native Method)
E/AndroidRuntime( 326): at java.lang.reflect.Method.invoke(Method.java:521)
E/AndroidRuntime( 326): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:860)
E/AndroidRuntime( 326): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618)
E/AndroidRuntime( 326): at dalvik.system.NativeStart.main(Native Method)
最佳答案
doInBackground 与 UI 线程不同步，这意味着您不能直接从该方法中操作 UI 元素、启动对话框等。修复很容易。只需将您的 AlertDialog 代码移动到 onPostExecute 方法( 与 UI 线程同步)。
在使用 AsyncTask 时，请记住:
doInBackground用于执行可能代价高昂的操作(网络访问、套接字连接、数据库查询等)onPostExecute是为了对结果做一些事情，如果你愿意的话(这个方法与 UI 线程同步，所以你可以直接操作 UI 元素)
关于java - 无法在 doInbackground() 方法中执行 AlertDialog，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/11218839/