Android 应用程序未打开警报对话框

Question

我正在制作一个需要互联网连接的安卓应用程序。当我连接到互联网时，该应用程序运行良好。我想要做的是，如果我没有连接到互联网，它必须显示一个警告对话框，通知用户它需要互联网连接。我正在使用异步任务将数据发送到服务器。异步任务的代码是：

protected class SendContacts extends AsyncTask<String,Void,String>
{
    @Override 
    protected String doInBackground(String... str) {

        String contactInfo;
        contactInfo=str[0];

        InputStream is = null;
        String result=new String(); 

        HttpClient httpclient = new DefaultHttpClient();
        HttpPost httppost = new HttpPost("http://johnconnor.comuf.com/myphp.php");

        try {
            List<NameValuePair> nameValuePairs = new ArrayList<NameValuePair>(1);
            nameValuePairs.add(new BasicNameValuePair("fullInfo", contactInfo));
           //   nameValuePairs.add(new BasicNameValuePair("lat",latitude));
           //   nameValuePairs.add(new BasicNameValuePair("lng",longitude));
            httppost.setEntity(new UrlEncodedFormEntity(nameValuePairs));
            HttpResponse response= httpclient.execute(httppost);
            Log.i("SendContacts Successful",response.getStatusLine().toString());
            HttpEntity entity = response.getEntity();
            is = entity.getContent(); 

        } catch (ClientProtocolException e) {
            Log.e("log_tag", "Error in http connection "+e.toString());
        } catch (IOException e) {
                        // When not connected to internet, it reach this catch block.How can i implement alert dialog here so that it can be displayed on main UI thread
            Log.e("log_tag","Error in http connection:"+e.toString());

           }
        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) {
        } 

    result=result.substring(0,result.indexOf('\n'));
    return result ;
}

}

这是我的日志：

08-19 14:48:15.130: D/ActivityThread(10279): setTargetHeapUtilization:0.25

08-19 14:48:15.130: D/ActivityThread(10279): setTargetHeapIdealFree:8388608

08-19 14:48:15.130: D/ActivityThread(10279): setTargetHeapConcurrentStart:2097152

08-19 14:48:15.220: D/AbsListView(10279): Get MotionRecognitionManager

08-19 14:48:15.490: E/log_tag(10279): Error in http connection:java.net.UnknownHostException: Unable to resolve host "johnconnor.comuf.com": No address associated with hostname

08-19 14:48:15.500: W/dalvikvm(10279): threadid=12: thread exiting with uncaught exception (group=0x41c66438)

08-19 14:48:15.510: W/dalvikvm(10279): threadid=11: thread exiting with uncaught exception (group=0x41c66438)

08-19 14:48:15.510: E/AndroidRuntime(10279): FATAL EXCEPTION: AsyncTask #2

08-19 14:48:15.510: E/AndroidRuntime(10279): java.lang.RuntimeException: An error occured while executing doInBackground()

08-19 14:48:15.510: E/AndroidRuntime(10279):    at android.os.AsyncTask$3.done(AsyncTask.java:299)

08-19 14:48:15.510: E/AndroidRuntime(10279):    at java.util.concurrent.FutureTask$Sync.innerSetException(FutureTask.java:273)

08-19 14:48:15.510: E/AndroidRuntime(10279):    at java.util.concurrent.FutureTask.setException(FutureTask.java:124)

08-19 14:48:15.510: E/AndroidRuntime(10279):    at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:307)

08-19 14:48:15.510: E/AndroidRuntime(10279):    at java.util.concurrent.FutureTask.run(FutureTask.java:137)

08-19 14:48:15.510: E/AndroidRuntime(10279):    at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:230)

08-19 14:48:15.510: E/AndroidRuntime(10279):    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1076)

08-19 14:48:15.510: E/AndroidRuntime(10279):    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:569)

08-19 14:48:15.510: E/AndroidRuntime(10279):    at java.lang.Thread.run(Thread.java:856)

08-19 14:48:15.510: E/AndroidRuntime(10279): Caused by: java.lang.StringIndexOutOfBoundsException: length=0; regionStart=0; regionLength=-1

08-19 14:48:15.510: E/AndroidRuntime(10279):    at java.lang.String.startEndAndLength(String.java:593)

08-19 14:48:15.510: E/AndroidRuntime(10279):    at java.lang.String.substring(String.java:1474)

08-19 14:48:15.510: E/AndroidRuntime(10279):    at com.example.findmyfriend.DatabaseConnection$RegisterMe.doInBackground(DatabaseConnection.java:121)

08-19 14:48:15.510: E/AndroidRuntime(10279):    at com.example.findmyfriend.DatabaseConnection$RegisterMe.doInBackground(DatabaseConnection.java:1)

08-19 14:48:15.510: E/AndroidRuntime(10279):    at android.os.AsyncTask$2.call(AsyncTask.java:287)

08-19 14:48:15.510: E/AndroidRuntime(10279):    at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:305)

08-19 14:48:15.510: E/AndroidRuntime(10279):    ... 5 more

Answer 1

您可以为 AsyncTask 覆盖 onProgressUpdate，它在主 UI 线程上运行。然后从doInBackground 调用publishProgress 来触发它。

protected class SendContacts extends AsyncTask<String,Void,String>
{
    AlertDialog dialog;

    public SendContacts() {
        //configure AlertDialog
        dialog = ...
    }

    @Override 
    protected String doInBackground(String... str) {

        String contactInfo;
        contactInfo=str[0];

        InputStream is = null;
        String result=new String(); 

        HttpClient httpclient = new DefaultHttpClient();
        HttpPost httppost = new HttpPost("http://johnconnor.comuf.com/myphp.php");

        try {
            List<NameValuePair> nameValuePairs = new ArrayList<NameValuePair>(1);
            nameValuePairs.add(new BasicNameValuePair("fullInfo", contactInfo));
           //   nameValuePairs.add(new BasicNameValuePair("lat",latitude));
           //   nameValuePairs.add(new BasicNameValuePair("lng",longitude));
            httppost.setEntity(new UrlEncodedFormEntity(nameValuePairs));
            HttpResponse response= httpclient.execute(httppost);
            Log.i("SendContacts Successful",response.getStatusLine().toString());
            HttpEntity entity = response.getEntity();
            is = entity.getContent(); 

        } catch (ClientProtocolException e) {
            Log.e("log_tag", "Error in http connection "+e.toString());
        } catch (IOException e) {
                        // When not connected to internet, it reach this catch block.How can i implement alert dialog here so that it can be displayed on main UI thread
            //Update progress
            publishProgress(null);
            Log.e("log_tag","Error in http connection:"+e.toString());

           }
        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) {
        } 

        result=result.substring(0,result.indexOf('\n'));
        return result ;
    }                               

    @Override
    //Invoked on the UI thread
    protected void onProgressUpdate(Void... progress) {
        dialog.show();
    }
}       

Answer 2

你可以做两件事：

方式1：您可以在那里使用runOnUIThread() 方法并在其中包含警报对话框的代码。文档说：It runs the specified action on the UI thread. If the current thread is the UI thread, then the action is executed immediately. If the current thread is not the UI thread, the action is posted to the event queue of the UI thread.

例如：

Your_Activity_Name.this.runOnUiThread(new Runnable() {

            @Override
            public void run() {
                // your stuff to update the UI
                showWaitDialog();

            }
        });

方式2： 您可以做的其他事情（并且是首选）是将Boolean 变量传递给onPostExecute。变量可以是true 成功和false 在任何失败的情况下。然后在那里你可以相应地显示对话框。