https://homeostasis.scs.carleton.ca/wiki/index.php?action=history&feed=atom&title=Mobile_App_Development_2022W_Lecture_14 2026-04-06T01:53:57Z Revision history for this page on the wiki MediaWiki 1.42.1 https://homeostasis.scs.carleton.ca/wiki/index.php?title=Mobile_App_Development_2022W_Lecture_14&diff=23873&oldid=prev 2022-03-09T20:06:01Z

<p>Created page with &quot;==Video== Video from the lecture given on March 9, 2022 is now available: * [https://homeostasis.scs.carleton.ca/~soma/mad-2022w/lectures/comp1601-2022w-lec14-20220309.m4v video] * [https://homeostasis.scs.carleton.ca/~soma/mad-2022w/lectures/comp1601-2022w-lec14-20220309.cc.vtt auto-generated captions] Video is also available through Brightspace (Resources-&gt;Zoom Meetings (Recordings, etc.)-&gt;Cloud Recordings tab). Note that here you&#039;ll also see chat messages. ==Notes=...&quot;</p> <p><b>New page</b></p><div>==Video==<br /> <br /> Video from the lecture given on March 9, 2022 is now available:<br /> * [https://homeostasis.scs.carleton.ca/~soma/mad-2022w/lectures/comp1601-2022w-lec14-20220309.m4v video]<br /> * [https://homeostasis.scs.carleton.ca/~soma/mad-2022w/lectures/comp1601-2022w-lec14-20220309.cc.vtt auto-generated captions]<br /> Video is also available through Brightspace (Resources-&gt;Zoom Meetings (Recordings, etc.)-&gt;Cloud Recordings tab). Note that here you&#039;ll also see chat messages.<br /> <br /> ==Notes==<br /> <br /> &lt;pre&gt;<br /> Lecture 14<br /> ----------<br /> - I&#039;ll be grading midterms soon, so should be another week, sorry<br /> - first want to release A3<br /> - rest of term is on Android<br /> <br /> Question for the day: why does textanalyzer-5 lose state when you rotate it,<br /> but TapDemo doesn&#039;t?<br /> - note that textanalyzer-5 keeps the text that you enter, it just<br /> forgets the mode you&#039;re in.<br /> <br /> So what&#039;s happening is the running activity is destroyed when you rotate the screen<br /> - and textanalyzer-5 doesn&#039;t save the state properly<br /> <br /> What&#039;s an activity?<br /> - the unit of execution in an android app<br /> - can have many activities<br /> - when you run an app in any way, you are actually running a specific activity<br /> - and of course there is a default activity that is run when<br /> you launch the app<br /> - when you have multiple screens, you can implement them as multiple activities<br /> - but really, it is about splitting up functionality, not the interface per se<br /> <br /> So in textanalyzer-5, the state variable analysisMode is forgotten because the activity was terminated and then restarted<br /> - note that EditText preserves its own state after rotation<br /> - but MainActivity doesn&#039;t, we have to implement that functionality<br /> <br /> <br /> onCreate in an activity is a method that is called when an activity is created<br /> - it has a single argument which is a Bundle<br /> - bundles are used to store state that can be saved and restored<br /> <br /> Basic idea with bundles<br /> - when your activity will be terminated, save state into a bundle<br /> - when your activity is created again, restore state from the given bundle<br /> <br /> Bundles are dictionaries that can hold different types of data<br /> - so key, value, with the value being able to have different types<br /> - and the key is a string<br /> - the Android runtime manages the instance state bundles,<br /> we just have to put data in and pull data out at the right times<br /> <br /> <br /> You should play with TapDemo and see when the different activity lifecycle methods are called<br /> - when you rotate the screen, switch to another app, terminate an app, etc<br /> <br /> <br /> So, why does Android terminate the activity when the screen is rotated?<br /> - because the interface has to be redrawn anyway, easist way is to<br /> kill the activity and start it again with new screen geometry<br /> <br /> What about iOS apps? Do they have a lifecycle?<br /> - yes definitely, much the same as Android<br /> - however, by default much of the state management is handled automatically<br /> - but you can change it<br /> <br /> How can we fix TapDemo so that it shows the proper count after rotation?<br /> &lt;/pre&gt;</div>

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