1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
|
/****************************************************************************
**
** Copyright (C) 2016 The Qt Company Ltd.
** Contact: https://www.qt.io/licensing/
**
** This file is part of the documentation of the Qt Toolkit.
**
** $QT_BEGIN_LICENSE:FDL$
** Commercial License Usage
** Licensees holding valid commercial Qt licenses may use this file in
** accordance with the commercial license agreement provided with the
** Software or, alternatively, in accordance with the terms contained in
** a written agreement between you and The Qt Company. For licensing terms
** and conditions see https://www.qt.io/terms-conditions. For further
** information use the contact form at https://www.qt.io/contact-us.
**
** GNU Free Documentation License Usage
** Alternatively, this file may be used under the terms of the GNU Free
** Documentation License version 1.3 as published by the Free Software
** Foundation and appearing in the file included in the packaging of
** this file. Please review the following information to ensure
** the GNU Free Documentation License version 1.3 requirements
** will be met: https://www.gnu.org/licenses/fdl-1.3.html.
** $QT_END_LICENSE$
**
****************************************************************************/
/*!
\page qtquick-debugging.html
\ingroup qtquick-tools
\title Debugging QML Applications
\brief debugging tools in QML
\section1 Console API
\section2 Log
\keyword console log
\c console.log, console.debug, console.info, console.warn and console.error can be used to print
debugging information to the console. For example:
\code
function f(a, b) {
console.log("a is ", a, "b is ", b);
}
\endcode
The output is generated using the qDebug, qWarning, qCritical methods in C++
(see also \l {Debugging Techniques}).
\section2 Assert
\keyword console assert
\c console.assert tests that an expression is true. If not, it will write an optional message
to the console and print the stack trace.
\code
function f() {
var x = 12
console.assert(x == 12, "This will pass");
console.assert(x > 12, "This will fail");
}
\endcode
\section2 Timer
\keyword console time
\keyword console timeEnd
\c console.time and console.timeEnd log the time (in milliseconds) that was spent between
the calls. Both take a string argument that identifies the measurement. For example:
\code
function f() {
console.time("wholeFunction");
console.time("firstPart");
// first part
console.timeEnd("firstPart");
// second part
console.timeEnd("wholeFunction");
}
\endcode
\section2 Trace
\keyword console trace
\c console.trace prints the stack trace of the JavaScript execution at the point where
it was called. The stack trace info contains the function name, file name, line number
and column number. The stack trace is limited to last 10 stack frames.
\section2 Count
\keyword console count
\c console.count prints the current number of times a particular piece of code has been executed,
along with a message. That is,
\code
function f() {
console.count("f called");
}
\endcode
will print \c{f called: 1}, \c{f called: 2} ... whenever \c{f()} is executed.
\section2 Profile
\keyword console profile
\c console.profile turns on the QML and JavaScript profilers. Nested calls are not
supported and a warning will be printed to the console.
\keyword console profileEnd
\c console.profileEnd turns off the QML and JavaScript profilers. Calling this function
without a previous call to console.profile will print a warning to the console. A
profiling client should have been attached before this call to receive and store the
profiling data. For example:
\code
function f() {
console.profile();
//Call some function that needs to be profiled.
//Ensure that a client is attached before ending
//the profiling session.
console.profileEnd();
}
\endcode
\section2 Exception
\keyword console exception
\c console.exception prints an error message together with the stack trace of JavaScript
execution at the point where it is called.
\section1 Debugging Module Imports
The \c QML_IMPORT_TRACE environment variable can be set to enable debug output
from QML's import loading mechanisms.
For example, for a simple QML file like this:
\qml
import QtQuick 2.3
Rectangle { width: 100; height: 100 }
\endqml
If you set \c {QML_IMPORT_TRACE=1} before running the \l{qtquick-qmlscene.html}
{QML Scene} (or your QML C++ application), you will see output similar to this:
\code
QQmlImportDatabase::addImportPath "/qt-sdk/imports"
QQmlImportDatabase::addImportPath "/qt-sdk/bin/QMLViewer.app/Contents/MacOS"
QQmlImportDatabase::addToImport 0x106237370 "." -1.-1 File as ""
QQmlImportDatabase::addToImport 0x106237370 "Qt" 4.7 Library as ""
QQmlImportDatabase::resolveType "Rectangle" = "QDeclarativeRectangle"
\endcode
\section1 QML Debugging Infrastructure
\keyword declarative_debug
\keyword qml debug
The \l{Qt QML} module provides services for debugging, inspecting, and profiling
applications via a TCP port.
\section2 Enabling the Infrastructure
You have to explicitly enable the debugging infrastructure when compiling your
application. If you use qmake, you can add the configuration parameters to
the project .pro file:
\list
\li Qt Quick 1: \c {CONFIG+=declarative_debug}
\li Qt Quick 2: \c {CONFIG+=qml_debug}
\endlist
If you use some other build system, you can pass the following defines to the
compiler:
\list
\li Qt Quick 1: \c {QT_DECLARATIVE_DEBUG}
\li Qt Quick 2: \c {QT_QML_DEBUG}
\endlist
\note Enabling the debugging infrastructure might compromise the integrity of
the application and system, and therefore, you should only enable it in a
controlled environment. When the infrastructure is enabled, the application
displays the following warning:
\c {QML debugging is enabled. Only use this in a safe environment.}
\section2 Starting Applications
Start the application with the following arguments:
\c {-qmljsdebugger=port:<port_from>[,port_to][,host:<ip address>][,block]}
Where \c {port_from} (mandatory) specifies either the debugging port or the
start port of a range of ports when \c {port_to} is specified, \c {ip address}
(optional) specifies the IP address of the host where the application is
running, and \c block (optional) prevents the application from running until the
debug client connects to the server. This enables debugging from the start.
After the application has successfully started, it displays the following
message:
\c {QML Debugger: Waiting for connection on port <port_number>}
\section2 Connecting to Applications
When the application is running, an IDE or a tool that implements the binary
protocol can connect to the open port.
Qt provides a \c qmlprofiler command line tool to capture profiling data in a
file. To run the tool, enter the following command:
\c {qmlprofiler -p <port> -attach <ip address>}
\section1 Debugging with Qt Creator
Qt Creator uses the debugging infrastructure to debug, inspect
and profile Qt Quick applications on the desktop as well as on remote devices.
Qt Creator provides integrated clients for debugging JS, inspecting the object
tree, and profiling the activities of a QML engine. For more information, see
\l{Qt Creator: Debugging Qt Quick Projects}.
*/
|
