Using trace methods – Apple WebObjects 3.5 User Manual
Page 59
Debugging Techniques
59
In WebScript and Objective-C,
logWithFormat:
works like the
printf()
function in
C. This method takes a format string and a variable number of additional
arguments. For example, the following code excerpt prints the string “The
value of myString is Elvis”:
myString = @"Elvis";
[self logWithFormat:@"The value of myString is %@", myString];
When this code is parsed, the value of
myString
is substituted for the
conversion specification
%@
. The conversion character @ indicates that the
data type of the variable being substituted is an object (that is, of the
id
data
type).
Because in WebScript all variables are objects, the conversion specification
you use must always be
%@
. Unlike
printf()
, you can’t supply conversion
specifications for primitive C data types such as
%d
,
%s
,
%f
, and so on. (If you
do, you might see the address of the variable rather than its value.)
In Java, the equivalent of
logWithFormat:
is
logString
, and you can send it only to
WebApplication objects. Instead of using
printf
specifications, it uses
concatenation. Here’s how you’d write the same lines of code in Java:
myString = "Elvis";
application().logString("The value of myString is " + myString);
Perhaps the most effective debugging technique is to use
logWithFormat:
to
print the contents of
self
. This prints the values of all of your component
variables. For example, this statement at the end of the
sayHello
method in
HelloWorld’s
Main.wos
:
[self logWithFormat:@"The contents of self in sayHello are %@", self];
produces output that resembles the following:
The contents of self in sayHello are
<<WOScriptedClass(/WebObjects/Examples/WebScript/HelloWorld.woa/Main
.wo/Main): 0x8cb08 name=Main subcomponents=0x0> visitorName=frank>
Here’s how you’d write the same line of code in Java:
application().logString("The contents of this in sayHello are "
+ this.toString());
Using Trace Methods
WOApplication (in Java, WebApplication) provides trace methods that log
different kinds of information about your running application. These