Retrieve weather forecast

deepnguyen

Hi,

I'm new to Qt. I'm trying to make a Qt GUI application to retrieve weather forecast information but I don't know where to start.

Can anyone guide me to do this please?

AcerExtensa

If you new to Qt, start with "tutorials":http://qt-project.org/doc/qt-4.8/tutorials.html.

About your subject:
Have you already found service which can provide you with weather forecast information? Start with that. Find one. There is many services wich provides this kind of information through simple REST request. For example Norway Weather Institute(search for yr.no API).
Also, mostly all such services wants Longitude & Latitude of place the weather forecast you are looking for. So you will need to convert real address into geographical point. It is also easy to do, google provides simple REST API for that.

All that information you can get with "QNAM":http://qt-project.org/doc/qt-4.8/qnetworkaccessmanager.html get request. (check examples provided in QNAM documentation)

Search for information I've wrote about, choose right service, start coding. It is easy task. If you will get in troubles with your code, ask for help with code snipped where you have got problem. Happy coding!

deepnguyen

thanks a lot, appreciate your quick reply. :)

issam

I think your project is somewhat similar to an RSS reader !
If so, you have to use XML.

deepnguyen

I decided to use QXmlStreamReader to read a simple xml code retrieve from "http://rss.weatherzone.com.au/?u=12994-1285&lt=aploc&lc=9388&obs=1&fc=1&warn=1"

but when i'm trying to debug the program exited with code 0xc0000139

I've been digging around on Google and still can't find the answer to my problem

Whenever I used anything involving Qtnetworkd4.dll it raise that problem. Not sure if my code in .pro is wrong or not though.

Here's the code sniplet of part of my project:

test.pro

@QT += core gui network xml

TARGET = Clock
TEMPLATE = app

SOURCES += main.cpp
mainwindow.cpp

HEADERS += mainwindow.h

FORMS += mainwindow.ui@

a push button in mainwindow:
@void MainWindow::on_pushButton_3_clicked()
{
QNetworkAccessManager networkAccessManager = new QNetworkAccessManager(this);
connect(networkAccessManager, SIGNAL(finished(QNetworkReply)),this, SLOT(slotFinished(QNetworkReply*)));
QUrl url("http://rss.weatherzone.com.au/?u=12994-1285&lt=aploc&lc=9388&obs=1&fc=1&warn=1");
QNetworkReply *reply = networkAccessManager->get(QNetworkRequest(url));connect(reply, SIGNAL(error(QNetworkReply::NetworkError)),this,SLOT(slotError( QNetworkReply::NetworkError)));
QXmlStreamReader reader( reply );
reader.readNext();
while (!reader.atEnd()) {
if (reader.isStartElement()) {
if (reader.name() == "title") {
reader.readNext();
if (reader.text() == "Brisbane weather forecast") {
//blah blah blah
}
}
}
}
}@

deepnguyen

by the way I'm using QtCreator 2.4.1 base on Qt 4.7.4(32 bit)

and one more question, when i'm trying to use the QtNetworkAccessManager I can't do
@#include <QtNetwork>@

but I have to
@#include <QtNetwork/QtNetworkAccessManager>@

the same for QtNetworkReply, QtNetworkRequest

anyone know the reason to this?

AcerExtensa

You should read reply in slotFinished().

@
void MainWindow::on_pushButton_3_clicked()
{

QNetworkAccessManager *networkAccessManager = new QNetworkAccessManager(this);
connect(networkAccessManager, SIGNAL(finished(QNetworkReply*)),this, SLOT(slotFinished(QNetworkReply*)));

QUrl url("http://rss.weatherzone.com.au/?u=12994-1285&lt=aploc&lc=9388&obs=1&fc=1&warn=1");

QNetworkReply *reply = networkAccessManager->get(QNetworkRequest(url));connect(reply, SIGNAL(error(QNetworkReply::NetworkError)),this,SLOT(slotError( QNetworkReply::NetworkError)));

}

void MainWindow::slotFinished(QNetworkReply* reply)
{
if(reply->error() != QNetworkReply::NoError)
{
qCritical() << reply->errorString();
return;
}
QXmlStreamReader reader( reply );
reader.readNext();
while (!reader.atEnd()) {
if (reader.isStartElement()) {
if (reader.name() == "title") {
reader.readNext();
if (reader.text() == "Brisbane weather forecast") {
//blah blah blah
}
}
}
}

}
@

deepnguyen

It raised the same error, the 0xc0000139 thing. Keep getting that every time i use QtNetwork

deepnguyen

When I tried to run the file in my debug folder with all the needed dll i got

Entry Point Not Found

The procedure entry point _Z15qIsEffectiveTLDRK7QString could not be located in the dynamic link library QtCored4.dll.

and if I try to debug it it raised

The program has unexpectedly finished.
C:\Users\DeepBlue\Documents\Qt\Clock-build-desktop-Qt_4_8_1_for_Desktop_-_MinGW__Qt_SDK__Debug\debug\Clock.exe exited with code -1073741511

I just know that -1073741511 = 0xc0000139.

AcerExtensa

I don't see possible error here. It is somewhere else... Set some breakpoints and debug your app step-by-step

deepnguyen

Well I managed to clean up the Build Environment and it works now, turn out I was using the wrong environment variables.

deepnguyen

now when I tried to debug i get 2 errors
Object::connect: No such slot MainWindow::slotFinished(QNetworkReply*) in ..\Clock\mainwindow.cpp:755
Object::connect: (receiver name: 'MainWindow')
Object::connect: No such slot MainWindow::slotError( QNetworkReply::NetworkError) in ..\Clock\mainwindow.cpp:757
Object::connect: (receiver name: 'MainWindow')

deepnguyen

Ok I know what to do now, thanks a lot AcerExtensa

deepnguyen

My code after I clean up a bit is

@void MainWindow::on_pushButton_3_clicked()
{

QNetworkAccessManager * manager = new QNetworkAccessManager(this);
connect(manager, SIGNAL(finished(QNetworkReply*)), this, SLOT(slotFinished(QNetworkReply*)));
QUrl url("http://rss.weatherzone.com.au/?u=12994-1285&lt=aploc&lc=9388&obs=1&fc=1&warn=1");

manager->get(QNetworkRequest(url));

}

void MainWindow::slotFinished(QNetworkReply* reply)
{
if(reply->error() != QNetworkReply::NoError)
{
qCritical() << reply->errorString();
return;
}
QXmlStreamReader reader( reply );
reader.readNext();
while (!reader.atEnd()) {
if (reader.isStartElement()) {
if (reader.name() == "title") {
reader.readNext();
if (reader.text() == "Brisbane weather forecast") {
//blah blah blah
qDebug()<< reader.text();
}
}
}
}

}@

When I debug, whenever I click the button the program freeze up. Where is the problem--?

deepnguyen

lol silly me, I didn't put

@reader.readNext();@

in the while loop, and I keep checking my slot connections

AcerExtensa

-Hm, it can be only because of while loop. but it should not take more then some seconds...-

deepnguyen

"
Tuesday

Mostly sunny
14°C - 25°C
Wednesday

Mostly sunny
14°C - 26°C
Thursday

Mostly sunny
13°C - 28°C
Friday

Mostly sunny
15°C - 32°C
"

I'm almost there but I need a way to split this string and my head is going dumb now. How can i get only the Days and the weather status?

AcerExtensa

the problem is, your choosen service returns RSS feed with forecast as simple html text in [CDATA]... So, you need to parse it yourself... For example with "QRegExp":http://qt-project.org/doc/qt-4.8/qregexp.html parse days first(there is only 7 days), after that parse temperature, it may always have format like:
+/- <min 1 digit - max 2digits>°<ignore symbols> - <ignore symbols> +/- <min 1 digit - max 2 digit>°

johndev

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