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Posted to users@wicket.apache.org by Abid K <ab...@gmail.com> on 2010/07/27 10:28:16 UTC
When object is null
I hope someone can help a newbie who is learning Wicket.
I have the following code which accepts a parameter and then does a database
query to get the 'Data' object. If the user enters the wrong Id the database
query will return null and in this case I want to notify the user the data
could not be found and any other component should be hidden.
But, when I get an null object the code stops working and a null exception
is thrown, any ideas? Or is there a elegant way to do this?
public class DataView extends WebPage {
private Data data;
public DataView(PageParameters parameters) {
long dataId = parameters.getLong("dataId");
DataDao dataDao = new DataDao();
data = dataDao.getData( dataId );
// display message that the data could not be found
Label dataNotFound = new Label("dataNotFound", "Data could not be
found");
dataNotFound.setVisible(data == null);
// otherwise display the panel containing the data
SomePanel panel = new SomePanel("somePanel");
panel.setVisible(data != null);
add(dataNotFound);
add(panel);
}
public class SomePanel extends Panel {
public SomePanel(String id) {
super(id);
// this throws null exception when data is null
Label label = new Label("someLabel", String.valueOf(data.getId()));
add(label);
}
}
}
Thanks
Re: When object is null
Posted by Iain Reddick <ia...@beatsystems.com>.
I've come across similar scenarios fairly often - i.e. where a the
construction of component is impossible if its model object is null, or
some other construction parameter is null.
I'm still not sure what the best approach is in this situation.
One of the methods I've used is to late-bind the "optional" component in
the onBeforeRender() of a special wrapper container (e.g. if the model
object != null, add the component, make the wrapper visible. If model
object == null, don't add the component and make the wrapper
non-visible). This seems like a blatant hack, however.
see these threads:
http://apache-wicket.1842946.n4.nabble.com/Nullable-resource-link-td1886391.html#a1886395
http://apache-wicket.1842946.n4.nabble.com/Components-and-nullable-data-td1888023.html#none
Abid K wrote:
> Thanks Josh and Daniel - both methods have worked. I have gone with checking
> if the object is null or not like so...
>
> public class SomePanel extends Panel {
> public SomePanel(String id) {
> super(id);
>
> if ( data == null ) {
> return;
> }
>
> Label label = new Label("someLabel", String.valueOf(data.getId()));
> add(label);
> }
> }
>
> I have decided to do this because I am not sure how I can format a date
> without doing this...
> SimpleDateFormat dateFormat = new SimpleDateFormat( "dd/MM/yyyy" );
> Label dateLabel = new Label( "date", dateFormat.format( data.getDate(
> ) ) );
>
> Thanks.
>
>
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Re: When object is null
Posted by Abid K <ab...@gmail.com>.
Thanks Josh and Daniel - both methods have worked. I have gone with checking
if the object is null or not like so...
public class SomePanel extends Panel {
public SomePanel(String id) {
super(id);
if ( data == null ) {
return;
}
Label label = new Label("someLabel", String.valueOf(data.getId()));
add(label);
}
}
I have decided to do this because I am not sure how I can format a date
without doing this...
SimpleDateFormat dateFormat = new SimpleDateFormat( "dd/MM/yyyy" );
Label dateLabel = new Label( "date", dateFormat.format( data.getDate(
) ) );
Thanks.
Re: When object is null
Posted by Daniel Soneira <da...@joyn-it.at>.
You could try using a PropertyModel instead like this:
Label label = new Label("someLabel", new
PropertyModel<String>(DataView.this,"data.id");
PropertyModels take care of possible null pointers.
Kind regards,
Daniel
www.joyn-it.at
On 27.07.2010 10:28, Abid K wrote:
> I hope someone can help a newbie who is learning Wicket.
>
> I have the following code which accepts a parameter and then does a database
> query to get the 'Data' object. If the user enters the wrong Id the database
> query will return null and in this case I want to notify the user the data
> could not be found and any other component should be hidden.
>
> But, when I get an null object the code stops working and a null exception
> is thrown, any ideas? Or is there a elegant way to do this?
>
> public class DataView extends WebPage {
>
> private Data data;
>
> public DataView(PageParameters parameters) {
> long dataId = parameters.getLong("dataId");
>
> DataDao dataDao = new DataDao();
> data = dataDao.getData( dataId );
>
> // display message that the data could not be found
> Label dataNotFound = new Label("dataNotFound", "Data could not be
> found");
> dataNotFound.setVisible(data == null);
>
> // otherwise display the panel containing the data
> SomePanel panel = new SomePanel("somePanel");
> panel.setVisible(data != null);
>
> add(dataNotFound);
> add(panel);
> }
>
> public class SomePanel extends Panel {
> public SomePanel(String id) {
> super(id);
> // this throws null exception when data is null
> Label label = new Label("someLabel", String.valueOf(data.getId()));
> add(label);
> }
> }
> }
>
> Thanks
>
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Re: When object is null
Posted by Josh Kamau <jo...@gmail.com>.
Abid,
Hi,
I noted that you are adding the panel whether the data is null or not. I
would suggest you do this;
Data data = dataDao.getData(id)
if (data!= null){
//construct and add the panel
DataPanel panel = new DataPanel("panel", data);
add(panel);
//the panel has implementation of what to do with the data once it is
passed to it.
} else {
//forget about the panel and only add the label that says there is no
data
add(new Label("No data to display"));
}
regards
Josh
On Tue, Jul 27, 2010 at 11:48 AM, Josh Kamau <jo...@gmail.com> wrote:
> Abid,
>
> Hi,
>
> I noted that you are adding the panel whether the data is null or not. I
> would suggest you do this;
>
> if (data!= null){
>
> //construct and add the panel
>
>
> }
>
> On Tue, Jul 27, 2010 at 11:28 AM, Abid K <ab...@gmail.com> wrote:
>
>> I hope someone can help a newbie who is learning Wicket.
>>
>> I have the following code which accepts a parameter and then does a
>> database
>> query to get the 'Data' object. If the user enters the wrong Id the
>> database
>> query will return null and in this case I want to notify the user the data
>> could not be found and any other component should be hidden.
>>
>> But, when I get an null object the code stops working and a null exception
>> is thrown, any ideas? Or is there a elegant way to do this?
>>
>> public class DataView extends WebPage {
>>
>> private Data data;
>>
>> public DataView(PageParameters parameters) {
>> long dataId = parameters.getLong("dataId");
>>
>> DataDao dataDao = new DataDao();
>> data = dataDao.getData( dataId );
>>
>> // display message that the data could not be found
>> Label dataNotFound = new Label("dataNotFound", "Data could not be
>> found");
>> dataNotFound.setVisible(data == null);
>>
>> // otherwise display the panel containing the data
>> SomePanel panel = new SomePanel("somePanel");
>> panel.setVisible(data != null);
>>
>> add(dataNotFound);
>> add(panel);
>> }
>>
>> public class SomePanel extends Panel {
>> public SomePanel(String id) {
>> super(id);
>> // this throws null exception when data is null
>> Label label = new Label("someLabel", String.valueOf(data.getId()));
>> add(label);
>> }
>> }
>> }
>>
>> Thanks
>>
>
>
Re: When object is null
Posted by Josh Kamau <jo...@gmail.com>.
Abid,
Hi,
I noted that you are adding the panel whether the data is null or not. I
would suggest you do this;
if (data!= null){
//construct and add the panel
}
On Tue, Jul 27, 2010 at 11:28 AM, Abid K <ab...@gmail.com> wrote:
> I hope someone can help a newbie who is learning Wicket.
>
> I have the following code which accepts a parameter and then does a
> database
> query to get the 'Data' object. If the user enters the wrong Id the
> database
> query will return null and in this case I want to notify the user the data
> could not be found and any other component should be hidden.
>
> But, when I get an null object the code stops working and a null exception
> is thrown, any ideas? Or is there a elegant way to do this?
>
> public class DataView extends WebPage {
>
> private Data data;
>
> public DataView(PageParameters parameters) {
> long dataId = parameters.getLong("dataId");
>
> DataDao dataDao = new DataDao();
> data = dataDao.getData( dataId );
>
> // display message that the data could not be found
> Label dataNotFound = new Label("dataNotFound", "Data could not be
> found");
> dataNotFound.setVisible(data == null);
>
> // otherwise display the panel containing the data
> SomePanel panel = new SomePanel("somePanel");
> panel.setVisible(data != null);
>
> add(dataNotFound);
> add(panel);
> }
>
> public class SomePanel extends Panel {
> public SomePanel(String id) {
> super(id);
> // this throws null exception when data is null
> Label label = new Label("someLabel", String.valueOf(data.getId()));
> add(label);
> }
> }
> }
>
> Thanks
>