| author | Shane McErlean <shane.mcerlean@accenture.com> |
| Fri, 27 Aug 2010 16:03:29 +0100 | |
| changeset 102 | 5d2aacefd978 |
| parent 1 | 2fb8b9db1c86 |
| permissions | -rw-r--r-- |
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<HTML><HEAD><TITLE>Using python to create Macintosh applications, part one</TITLE></HEAD> |
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<BODY> |
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<H1>Using python to create Macintosh applications, part one</H1> |
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<HR> |
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This document will show you how to create a simple mac-style |
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application using Python. We will glance at how to use dialogs and |
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resources. <p> |
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The example application we look at will be a simple program with a |
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dialog that allows you to perform domain name lookups on IP addresses |
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and hostnames. |
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The <A HREF="example1/dnslookup-1.py">source code</A> and |
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<A HREF="example1/dnslookup-1.rsrc">resource file</A> |
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for this application are available in the <A |
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HREF="example1">example1</A> folder (which you will have to download |
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if you are reading this document over the net and if you want to look |
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at the resources). <p> |
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We will use the builtin module "socket" that allows a |
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Python program to perform all sorts of networking functions, and we |
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will create the user interface around that. You should be able to run |
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the sample code with the standard Python distribution.<p> |
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<CITE> |
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If you are interested in building your own extensions to python you |
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should check out the companion document <A |
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HREF="plugins.html">Creating Macintosh Python C extensions</A>, |
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which tells you how to build your own C extension. |
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<p> |
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</CITE> |
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<H2><A NAME="dialog-resources">Creating dialog resources</A></H2> |
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Let us start with the creative bit: building the dialogs and creating |
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an icon for our program. For this you need ResEdit, and a reasonable |
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working knowledge of how to use it. "Inside Mac" or various books on |
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macintosh programming will help here. <p> |
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There is one fine point that deserves to be mentioned here: <A |
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NAME="resource-numbering">resource numbering</A>. Because often your |
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resources will be combined with those that the Python interpreter and |
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various standard modules need you should give your DLOG and DITL |
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resources numbers above 512. 128 and below are reserved for Apple, |
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128-228 are for extensions like Tk, |
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228-255 for the Python interpreter and 256-511 for standard |
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modules. If you are writing a module that you will be distributing for |
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inclusion in other people's programs you may want to register a number |
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in the 256-511 range, contact Guido or myself or whoever you think is |
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"in charge" of Python for the Macintosh at the moment. Even though the |
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application we are writing at the moment will keep its resources in a |
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separate resource file it is still a good idea to make sure that no |
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conflicts arise: once you have opened your resource file any attempt |
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by the interpreter to open a dialog will also search your resource |
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file. <p> |
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Okay, let's have a look at dnslookup-1.rsrc, our resource file. |
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The DLOG and accompanying DITL resource both have number 512. Since |
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ResEdit creates both with default ID=128 you should take care to |
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change the number on both. The dialog itself is pretty basic: two |
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buttons (Lookup and Quit), two labels and |
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two text entry areas, one of which is used for output only. Here's what |
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the dialog will look like at run time<p> |
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<div align=center> |
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<img width=324 height=189 src="example1/dnslookup-1.gif" alt="dialog image"> |
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</div> |
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<p> |
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<H2><A NAME="modal-dialog">An application with a modal dialog</A></H2> |
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Next, we will have to write the actual application. For this example, |
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we will use a modal dialog. This means that we will put up the dialog |
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and go into a loop asking the dialog manager for events (buttons |
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pushed). We handle the actions requested by the user until the Quit |
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button is pressed, upon which we exit our loop (and the program). This |
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way of structuring your program is actually rather antisocial, since |
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you force the user to do whatever you, the application writer, happen |
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to want. A modal dialog leaves no way of escape whatsoever (except |
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command-option-escape), and is usually not a good way to structure |
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anything but the most simple questions. Even then: how often have you |
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been confronted with a dialog asking a question that you could not |
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answer because the data you needed was obscured by the dialog itself? |
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In the next example we will look at an application that does pretty |
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much the same as this one but in a more user-friendly way. <p> |
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The code itself is contained in the file <A |
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HREF="example1/dnslookup-1.py"> dnslookup-1.py</A>. Have |
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a copy handy before you read on. The file starts off with a |
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textstring giving a short description. Not many tools do anything with |
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this as yet, but at some point in the future we <EM>will</EM> have all |
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sorts of nifty class browser that will display this string, so just |
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include it. Just put a short description at the start of each module, |
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class, method and function. After the initial description and some |
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comments, we import the modules we need. <p> |
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<A NAME="easydialogs"><CODE>EasyDialogs</CODE></A> is a handy standard |
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module that provides you with routines that put up common text-only |
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modal dialogs: |
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100 |
<UL> |
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|
101 |
<LI> <CODE>Message(str)</CODE> |
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|
102 |
displays the message "str" and an OK button, |
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|
103 |
<LI> <CODE>AskString(prompt, default)</CODE> |
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|
104 |
asks for a string, displays OK and Cancel buttons, |
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|
105 |
<LI> <CODE>AskYesNoCancel(question, default)</CODE> |
|
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
106 |
displays a question and Yes, No and Cancel buttons. |
|
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
107 |
</UL> |
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108 |
|
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|
109 |
<A NAME="res"><CODE>Res</CODE></A> is a pretty complete interface to |
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|
110 |
the MacOS Resource Manager, described fully in Inside Mac. There is |
|
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Initial QEMU (symbian-qemu-0.9.1-12) import
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111 |
currently no documentation of it, but the Apple documentation (or |
|
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
112 |
Think Ref) will help you on your way if you remember two points: |
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113 |
<UL> |
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114 |
<LI> Resources are implemented as Python objects, and each routine |
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115 |
with a resource first argument is implemented as a python method. |
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116 |
<LI> When in doubt about the arguments examine the routines docstring, |
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117 |
as in <CODE>print Res.OpenResFile.__doc__</CODE> |
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118 |
</UL> |
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119 |
|
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120 |
Similarly, <A NAME="dlg"><CODE>Dlg</CODE></A> is an interface to the |
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121 |
Dialog manager (with Dialogs being implemented as python objects and |
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122 |
routines with Dialog arguments being methods). The sys module you |
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|
123 |
know, I hope. The string module is an often used module that enables |
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124 |
you to perform many string related operations. In this case however, we |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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125 |
are only using the "digits" constant from the string module. We could |
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126 |
have simply defined "digits" as "0123456789". The socket module enables |
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|
127 |
us to perform the domain name lookups. We |
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|
128 |
use two calls from it: |
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129 |
<UL> |
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130 |
<LI> <CODE>gethostbyaddr()</CODE> |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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131 |
returns the hostname associated with an IP address |
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132 |
<LI> <CODE>gethostbyname()</CODE> |
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133 |
returns the IP address associated with a hostname |
|
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134 |
</UL> |
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135 |
|
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136 |
Next in the source file we get definitions for our dialog resource |
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137 |
number and for the item numbers in our dialog. These should match the |
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|
138 |
situation in our resource file dnslookup-1.rsrc, |
|
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139 |
obviously.<p> |
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140 |
|
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141 |
On to the main program. We start off with opening our resource file, |
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142 |
which should live in the same folder as the python source. If we |
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143 |
cannot open it we use <CODE>EasyDialogs</CODE> to print a message and |
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144 |
exit. You can try it: just move the resource file somewhere else for a |
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145 |
moment. Then we call do_dialog() to do the real work. <p> |
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|
146 |
|
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147 |
<CODE>Do_dialog()</CODE> uses <CODE>Dlg.GetNewDialog()</CODE> to open |
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148 |
a dialog window initialized from 'DLOG' resource ID_MAIN and putting |
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|
149 |
it on screen in the frontmost position. Next, we go into a loop, |
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|
150 |
calling <CODE>Dlg.ModalDialog()</CODE> to wait for the next user |
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|
151 |
action. <CODE>ModalDialog()</CODE> will return us the item number that |
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|
152 |
the user has clicked on (or otherwise activated). It will handle a few |
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|
153 |
slightly more complicated things also, like the user typing into |
|
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|
154 |
simple textfields, but it will <EM>not</EM> do things like updating |
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|
155 |
the physical appearance of radio buttons, etc. See Inside Mac or |
|
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
156 |
another programming guide for how to handle this |
|
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|
157 |
yourself. Fortunately, our simple application doesn't have to bother with this, |
|
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|
158 |
since buttons and textfields are the only active elements we have. So, we do a |
|
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|
159 |
simple switch on item number and call the appropriate routine to implement the |
|
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|
160 |
action requested. Upon the user pressing "Quit" we simply leave the loop and, |
|
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|
161 |
hence, <CODE>do_dialog()</CODE>. This will cause the python dialog object |
|
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|
162 |
<CODE>my_dlg</CODE> to be deleted and the on-screen dialog to disappear. <p> |
|
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
163 |
|
|
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|
164 |
<A NAME="dialog-warning">Time for a warning</A>: be very careful what |
|
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|
165 |
you do as long as a dialog is on-screen. Printing something, for |
|
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
166 |
instance, may suddenly cause the standard output window to appear over |
|
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
167 |
the dialog, and since we took no measures to redraw the dialog it will |
|
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
168 |
become very difficult to get out of the dialog. Also, command-period |
|
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
169 |
may or may not work in this situation. I have also seen crashes in |
|
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
170 |
such a situation, probably due to the multiple event loops involved or |
|
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
171 |
some oversight in the interpreter. You have been warned. <p> |
|
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
172 |
|
|
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|
173 |
The implementation of the "Lookup" command can use a bit more |
|
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
174 |
explaining: we get the necessary information with <CODE>dnslookup()</CODE> |
|
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
175 |
but now we have to update the on-screen dialog to present this |
|
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
176 |
information to the user. The <CODE>GetDialogItem()</CODE> method of |
|
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
177 |
the dialog returns three bits of information about the given item: its |
|
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
178 |
type, its data handle and its rect (the on-screen <CODE>x,y,w,h</CODE> |
|
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|
179 |
coordinates). We are only interested in the data handle here, on which |
|
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|
180 |
we call <CODE>SetDialogItemText()</CODE> to set our new text. Note |
|
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
181 |
here that python programmers need not bother with the C-string versus |
|
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
182 |
pascal-string controversy: the python glue module knows what is needed |
|
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
183 |
and converts the python string to the correct type. <p> |
|
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
184 |
|
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|
185 |
And that concludes our first example of the use of resources and |
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|
186 |
dialogs. Next, you could have a look at the source of EasyDialogs for |
|
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|
187 |
some examples of using input fields and filterprocs. Or, go on with |
|
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
188 |
reading the <A HREF="example2.html">second part</A> of this document |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
189 |
to see how to implement a better version of this application.<p> |
|
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
190 |
|
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|
191 |
</BODY> |
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|
192 |
</HTML> |
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|
193 |