LAMW - ungraceful exit
lazarus / 43-Android

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CC · 2019-06-30 18:08

Hi,

A LAMW application exits without a beep  in a situation like this:

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i  
aComponent:= nil;  aComponent.Tag:=1; 

An android  application built with Delphi at least displays an access
violation message. Maybe there is something to learn from Delphi here.
Maybe the difference  is in the Java part ...

An other related issue is that none of them actually executes the
exception handling part of a try ..... except block in such a case.
This makes proper exception handling impossible.

These problems are so fundamental. Unhandled exceptions  can cause
terrible user experience and lots  of bad user reviews.

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jmpessoa · 2019-06-30 19:45

There is a workaround here:

"AppPascalLibExceptionHandlerDemo1"

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CC · 2019-07-01 09:11

jmpessoa,

thanks for the tip, but unfortunately this does nor work for my
original problem above (referencing a null pointer);

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CC · 2019-07-01 09:27

Wow, I assumed not handling the null pointer exception was an
FPC/DELPHI issue, but it  turns out it is deeper than that:

https://howtodoinjava.com/java/exception-handling/how-to-effectively-
handle-nullpointerexception-in-java/

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CC · 2019-07-01 09:37

So it basically says that  we need to check for null manually all the
time.  The main point is to be able to catch the exceptions the
developers missed in a graceful manner. What I would see as an
accaptable solution is  to have  application level  exception handling
for all the exceptions not dealt with so it could report a stacktrace
to the developer and display a user friendly message to the user.

Maybe something like  this can be the solution:

Code: Java  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i public
class BaseActivity extends Activity {    @Override    public void
onCreate() {        super.onCreate();         final
Thread.UncaughtExceptionHandler oldHandler =           
Thread.getDefaultUncaughtExceptionHandler();        
Thread.setDefaultUncaughtExceptionHandler(            new
Thread.UncaughtExceptionHandler() {                @Override         
     public void uncaughtException(                    Thread
paramThread,                    Throwable paramThrowable             
 ) {                    //Do your own error handling here            
       if (oldHandler != null)                       
oldHandler.uncaughtException(                            paramThread, 
                          paramThrowable                        );
//Delegates to Android's error handling                    else      
                System.exit(2); //Prevents the service/app from
freezing                }            });    }}

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CC · 2019-07-01 10:14

I will think this through, just thinking loudly here:

Something like https://github.com/ACRA/acra can be one way to  go,  or
something like this:

Code: Java  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i public
class CustomExceptionHandler implements UncaughtExceptionHandler {   
private UncaughtExceptionHandler defaultUEH;     private String
localPath;     private String url;     /*      * if any of the
parameters is null, the respective functionality      * will not be
used      */    public CustomExceptionHandler(String localPath, String
url) {        this.localPath = localPath;        this.url = url;     
 this.defaultUEH = Thread.getDefaultUncaughtExceptionHandler();    }  
  public void uncaughtException(Thread t, Throwable e) {        String
timestamp = TimestampFormatter.getInstance().getTimestamp();       
final Writer result = new StringWriter();        final PrintWriter
printWriter = new PrintWriter(result);       
e.printStackTrace(printWriter);        String stacktrace =
result.toString();        printWriter.close();        String filename
= timestamp + ".stacktrace";         if (localPath != null) {        
  writeToFile(stacktrace, filename);        }        if (url != null)
{            sendToServer(stacktrace, filename);        }        
defaultUEH.uncaughtException(t, e);    }     private void
writeToFile(String stacktrace, String filename) {        try {       
   BufferedWriter bos = new BufferedWriter(new FileWriter(           
       localPath + "/" + filename));           
bos.write(stacktrace);            bos.flush();           
bos.close();        } catch (Exception e) {           
e.printStackTrace();        }    }     private void
sendToServer(String stacktrace, String filename) {       
DefaultHttpClient httpClient = new DefaultHttpClient();       
HttpPost httpPost = new HttpPost(url);        List<NameValuePair> nvps
= new ArrayList<NameValuePair>();        nvps.add(new
BasicNameValuePair("filename", filename));        nvps.add(new
BasicNameValuePair("stacktrace", stacktrace));        try {          
httpPost.setEntity(                    new UrlEncodedFormEntity(nvps,
HTTP.UTF_8));            httpClient.execute(httpPost);        } catch
(IOException e) {            e.printStackTrace();        }    }}