Make error checking in QSignalSpy consistent

QSignalSpy's constructor failed gracefully for some problems with the
parameters, but not for null parameters, for which there was only a
Q_ASSERT.  This commit makes the handling of null parameters consistent
with the handling of other errors -- output a meaningful error message
with qWarning() and return, so that isValid() will subsequently return
false.

Change-Id: I7f5677a4c10185e30403ce3e12a022de8c13bc1c
Task-number: QTBUG-14283
Reviewed-by: Rohan McGovern

1 files changed, 5 insertions, 1 deletions

diff --git a/src/testlib/qsignalspy.qdoc b/src/testlib/qsignalspy.qdoc
index 0c22868852..83dcccede2 100644
--- a/src/testlib/qsignalspy.qdoc
+++ b/src/testlib/qsignalspy.qdoc
@@ -62,7 +62,11 @@
 /*! \fn QSignalSpy::QSignalSpy(QObject *object, const char *signal)
 
     Constructs a new QSignalSpy that listens for emissions of the \a signal
-    from the QObject \a object. Neither \a signal nor \a object can be null.
+    from the QObject \a object. If QSignalSpy is not able to listen for a
+    valid signal (for example, because \a object is null or \a signal does
+    not denote a valid signal of \a object), an explanatory warning message
+    will be output using qWarning() and subsequent calls to \c isValid() will
+    return false.
 
     Example:
     \snippet doc/src/snippets/code/doc_src_qsignalspy.cpp 4