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<?xml version="1.0" encoding="utf-8"?>
<feed xmlns="http://www.w3.org/2005/Atom">
<title><![CDATA[Locadz Blog]]></title>
<link href="http://blog.locadz.com//atom.xml" rel="self"/>
<link href="http://blog.locadz.com//"/>
<updated>2012-04-21T17:05:31+08:00</updated>
<id>http://blog.locadz.com//</id>
<author>
<name><![CDATA[Locadz Team]]></name>
</author>
<generator uri="http://octopress.org/">Octopress</generator>
<entry>
<title type="html"><![CDATA[透過 Locadz 最大化 App 華文廣告效應]]></title>
<link href="http://blog.locadz.com//blog/2012/04/21/maximize-ad-revenue-in-chinese-market/"/>
<updated>2012-04-21T01:55:00+08:00</updated>
<id>http://blog.locadz.com//blog/2012/04/21/maximize-ad-revenue-in-chinese-market</id>
<content type="html"><![CDATA[<p>在這篇文章中，我將一步步的講解，如何透過 Locadz 來將你的 App 的華文廣告效應最大化。</p>
<div class="section" id="locadz">
<h2>註冊一個 Locadz 的帳號</h2>
<p>註冊 Locadz 帳號是一件簡單的事，我們使用 OpenID 的方式來管理你的帳號，你可以使用任何第三
方的 OpenID 帳號如 GMail or Yahoo 帳號，來登入 Locadz ；我們只保存你的 email 資訊，其
餘資料，仍是保存在你原始的帳號提供者那邊，你也不用煩惱需要多記一組密碼。</p>
<img alt="/images/2012-04-21/sign-up.png" src="http://blog.locadz.com//images/2012-04-21/sign-up.png" />
</div>
<div class="section" id="adunit">
<h2>註冊一個 AdUnit 區塊</h2>
<p>接著，你需要幫你的 App 註冊一個 AdUnit 區塊，AdUnit是 Locadz 管理廣告區域的基本
元素，一個 AdUnit 代表了一個 App 中可以用來顯示的廣告區塊，一個 App 中，可以定意許多的廣告區塊，如下圖。</p>
<p>圖片</p>
<p>各個廣告區塊，可以分別有不同的廣告商設定，例如，螢幕最上端的可以放來自廣告商的廣告，而在營幕
最底部的，則是放您自己其它 App 的廣告或 HouseAD。在 Locadz 這邊，會對各廣告區塊，分別追蹤
廣告的撥放次數及點擊次數。</p>
</div>
<div class="section" id="id1">
<h2>設定 AdUnit 的廣告商</h2>
<p>Locadz 最大的特色就是，能夠讓你「在地化你的廣告商」，在接下來的圖片範例中，將使用幾個廣
告商於不同的區域。</p>
<ul class="simple">
<li>在台灣，50%的流量到 VPon.tw</li>
<li>在台灣，50%的流量到 Kusogi</li>
<li>在中國，100%的流量到 VPon.cn</li>
<li>在其餘的世界各地， 100%的流量到 Google AdMob</li>
</ul>
<p>請遵循下圖的指示，一步步的透過 Web UI ，完成對一個 AdUnit 的設定。</p>
<iframe src="http://files.photosnack.com/iframe/embed.html?hash=pu801yqf&bgcolor=EEEEEE&wmode=window&t=1334913460"
width="600" height="400" seamless="seamless" scrolling="no" frameborder="0" allowtransparency="true"></iframe></div>
<div class="section" id="sdk">
<h2>將 SDK 加入專案</h2>
<div class="tip">
<p class="first admonition-title">Tip</p>
<p class="last">example project is available at <a class="reference external" href="mailto:git@github.com">git@github.com</a>:locadz/android-sdk-example.git
你可以參照這個範例專案來設定 Locadz SDK</p>
</div>
</div>
<div class="section" id="rd-party-sdk">
<h2>下載 3rd Party SDK</h2>
<p>首先，你要自 AdMob, VPon, Kusogi 的網站，下載相關的 Android SDK，</p>
</div>
<div class="section" id="androidmanifest-xml">
<h2>修改 AndroidManifest.xml</h2>
<p>接著，你需要修改你個 AndroidManifest.xml 加入底下這個部份，</p>
<figure class="code"><div class="highlight"><table><tr><td class="gutter"><pre class="line-numbers"><span class="line-number">1</span>
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</pre></td><td class="code"><pre><code class="text"><span class="line"><!-- AdMob integration -->
</span><span class="line"><activity android:name="com.google.ads.AdActivity"
</span><span class="line"> android:configChanges="orientation|keyboard|keyboardHidden|screenLayout|uiMode|screenSize|smallestScreenSize" />
</span><span class="line">
</span><span class="line"><!-- KuAD Integration -->
</span><span class="line"><activity android:name="com.kuad.ADDisplay"/>
</span><span class="line">
</span><span class="line"><!-- VPon integration -->
</span><span class="line"><activity
</span><span class="line"> android:name="com.vpon.adon.android.WebInApp"
</span><span class="line"> android:screenOrientation="portrait"
</span><span class="line"> android:configChanges="orientation|keyboardHidden|navigation|keyboard"
</span><span class="line"> android:label="@string/app_name"/>
</span><span class="line"><activity
</span><span class="line"> android:name="com.vpon.adon.android.CrazyAdRun"
</span><span class="line"> android:configChanges="orientation|keyboardHidden|navigation|keyboard"
</span><span class="line"> android:label="@string/app_name"
</span><span class="line"> android:theme="@android:style/Theme.Translucent" />
</span><span class="line"><activity
</span><span class="line"> android:name="com.vpon.adon.android.webClientHandler.QRActivity"
</span><span class="line"> android:finishOnTaskLaunch = "true"
</span><span class="line"> android:clearTaskOnLaunch = "true"
</span><span class="line"> android:configChanges="keyboardHidden|navigation|keyboard"/>
</span><span class="line"><activity
</span><span class="line"> android:name="com.vpon.adon.android.webClientHandler.ShootActivity"
</span><span class="line"> android:finishOnTaskLaunch = "true"
</span><span class="line"> android:clearTaskOnLaunch = "true"
</span><span class="line"> android:configChanges="keyboardHidden|navigation|keyboard"/>
</span><span class="line"><activity
</span><span class="line"> android:name="com.googleing.zxinging.client.android.HelpActivity"
</span><span class="line"> android:finishOnTaskLaunch = "true"
</span><span class="line"> android:clearTaskOnLaunch = "true"
</span><span class="line"> android:configChanges="keyboardHidden|navigation|keyboard"/>
</span><span class="line"><activity
</span><span class="line"> android:name="com.googleing.zxinging.client.android.CaptureActivity"
</span><span class="line"> android:finishOnTaskLaunch = "true"
</span><span class="line"> android:clearTaskOnLaunch = "true"
</span><span class="line"> android:configChanges="orientation|keyboardHidden"
</span><span class="line"> android:screenOrientation="landscape"
</span><span class="line"> android:theme="@android:style/Theme.NoTitleBar.Fullscreen"
</span><span class="line"> android:windowSoftInputMode="stateAlwaysHidden">
</span><span class="line"> <intent-filter>
</span><span class="line"> <action android:name="com.googleing.zxinging.client.android.SCAN"/>
</span><span class="line"> <category android:name="android.intent.category.DEFAULT"/>
</span><span class="line"> </intent-filter>
</span><span class="line"></activity>
</span><span class="line"><!-- end of Vpon -->
</span><span class="line">
</span><span class="line"><!-- set required permission -->
</span><span class="line"><uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION"/>
</span><span class="line"><uses-permission android:name="android.permission.ACCESS_NETWORK_STATE"/>
</span><span class="line"><uses-permission android:name="android.permission.INTERNET"/>
</span><span class="line"><uses-permission android:name="android.permission.READ_PHONE_STATE" />
</span></code></pre></td></tr></table></div></figure></div>
<div class="section" id="adunitlayout-ui-xml">
<h2>將 AdUnitLayout 加入 ui.xml</h2>
<p>最後是把 AdUnitLayout 放置到 UI 上，用來顯示廣告的區塊，同時，你要把這個區會的 ID 設定在這邊
，ADUNIT ID可以從網頁上得知，ADUNIT ID的格式為 <strong>00000000-0000-0000-0000-000000000000</strong> 的32位元字串。</p>
<figure class="code"><div class="highlight"><table><tr><td class="gutter"><pre class="line-numbers"><span class="line-number">1</span>
<span class="line-number">2</span>
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</pre></td><td class="code"><pre><code class="xml"><span class="line"><span class="nt"><com.locadz.AdUnitLayout</span>
</span><span class="line"> <span class="na">android:id=</span><span class="s">"@+id/adwhirl_layout"</span>
</span><span class="line"> <span class="na">android:layout_width=</span><span class="s">"fill_parent"</span>
</span><span class="line"> <span class="na">android:layout_height=</span><span class="s">"wrap_content"</span>
</span><span class="line"> <span class="na">locadz:adunit_id=</span><span class="s">"${YOUR_ADUNIT_ID}"</span> <span class="nt">/></span>
</span></code></pre></td></tr></table></div></figure></div>]]></content>
</entry>
<entry>
<title type="html"><![CDATA[Lesson Learned form Developing Locadz SDK]]></title>
<link href="http://blog.locadz.com//blog/2012/04/20/lesson-learned-from-developing-locadz-sdk/"/>
<updated>2012-04-20T23:07:00+08:00</updated>
<id>http://blog.locadz.com//blog/2012/04/20/lesson-learned-from-developing-locadz-sdk</id>
<content type="html"><![CDATA[<div class="section" id="introduction">
<h2>Introduction</h2>
<p>市面上大部份講 Android 的書，多數都是在講 API 要怎麼樣使用，但是，許多的書都沒有提到一個重要的問題，就是什
麼是 UI Thread (有時被稱做Main Thread) ，為什麼要有 UI Thread 以及為什麼不可以在 UI Thread 中執行耗時間的運算。</p>
<p>在本文中，我講談一談我們在開發Locadz SDK所使用到的一些技巧。</p>
</div>
<div class="section" id="ui-thread">
<h2>UI Thread</h2>
<p>UI Thread是Android(or other GUI library)用來處理 Event 的 thread ，這些 Event 可能是使用者處發的，如
Touch Event，或者是其它程式或者是系統底層的事件，如 Intent 或 <a class="reference external" href="http://developer.android.com/reference/android/location/LocationListener.html">Location Updates</a>.</p>
<p>在 UI Thread 處理完一個事件後， UI Thread 會重畫整個 Application ，而前面這句話解釋了處理 ANR 的兩個原則</p>
<ul class="simple">
<li>UI事件的處理要越快越好，在處理完前，UI不會有反應</li>
<li>UI的更新，一定要發生在UI Thread，要不然，要等到下次UI Event被處發時才會一併被處理</li>
</ul>
</div>
<div class="section" id="lesson-i-use-weakreference-to-avoid-strong-reference-and-memory-leak">
<h2>Lesson I: Use WeakReference to Avoid Strong Reference and Memory Leak</h2>
<p>有許多的文章談到如何用 <a class="reference external" href="http://developer.android.com/reference/android/os/AsyncTask.html">AsyncTask</a> 或 <a class="reference external" href="http://stackoverflow.com/questions/3197335/restful-api-service/3197456#3197456">ResultReceiver</a> 來把需要大量運算的程式，放在另一個 Thread 來做處理。</p>
<p>然而，這些範例都有著一個常備忽略的問題，那就是，這些 AsyncTask or ResultReceiver 常會把前景的Activity包進來
，如果說你的程式只有一個 Activity 的話，這或許不是什麼問題，但是若是你的 App 有多個畫面的話，這些在背景執行的程
式可能就會讓你的程式有 memory leak 的問題；如某家廣告商的 SDK 就有此問題。</p>
<p>一個可能的發生狀況是，Activity A透過 AsyncTask 去遠端下載一個圖片來顯示在 <em>Activity A</em> 之上，但因為某些因素
(如忘了設 connection timeout)，這個下載的程緒卡住了，既使 User 以從 <em>Activity A</em> 切換到 <em>Activity B</em> 之
上，這個 <em>Activity A</em> 還是不會被 GC 回收掉。</p>
<p>要避開因為有個 Strong Reference 造成 Activity 無法被回收的問題，我們在把有可能被回收的物件傳到另一個 Thread 中
被延後執行時，必需用 <a class="reference external" href="http://docs.oracle.com/javase/1.5.0/docs/api/java/lang/ref/WeakReference.html">WeakReference</a> 包住這個物件；如此一來，當Garbage Collector碰到一個已經不在前景的 Activity
時，Garbage Collector會把這物件處理掉，如此一來，就不會有 memory leak 的問題。</p>
<figure class="code"><div class="highlight"><table><tr><td class="gutter"><pre class="line-numbers"><span class="line-number">1</span>
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</pre></td><td class="code"><pre><code class="java"><span class="line"><span class="cm">/**</span>
</span><span class="line"><span class="cm"> * AsyncTask to Load Image</span>
</span><span class="line"><span class="cm"> */</span>
</span><span class="line"><span class="kd">public</span> <span class="kd">class</span> <span class="nc">DownloadImagesTask</span> <span class="kd">extends</span> <span class="n">AsyncTask</span><span class="o"><</span><span class="n">Uri</span><span class="o">,</span> <span class="n">Void</span><span class="o">,</span> <span class="n">Bitmap</span><span class="o">></span> <span class="o">{</span>
</span><span class="line">
</span><span class="line"> <span class="n">WeakReference</span><span class="o"><</span><span class="n">imageview</span><span class="o">></span> <span class="n">imageViewWeakReference</span> <span class="o">=</span> <span class="kc">null</span><span class="o">;</span>
</span><span class="line">
</span><span class="line"> <span class="kd">public</span> <span class="nf">DownloadImagesTask</span><span class="o">(</span><span class="n">ImageView</span> <span class="n">imageView</span><span class="o">)</span> <span class="o">{</span>
</span><span class="line"> <span class="n">imageViewWeakReference</span> <span class="o">=</span> <span class="k">new</span> <span class="n">WeakReference</span><span class="o"><</span><span class="n">Imageview</span><span class="o">>(</span><span class="n">imageView</span><span class="o">);</span>
</span><span class="line"> <span class="o">}</span>
</span><span class="line">
</span><span class="line"> <span class="nd">@Override</span>
</span><span class="line"> <span class="kd">protected</span> <span class="n">Bitmap</span> <span class="nf">doInBackground</span><span class="o">(</span><span class="n">Uri</span><span class="o">...</span> <span class="n">uri</span><span class="o">)</span> <span class="o">{</span>
</span><span class="line"> <span class="k">return</span> <span class="nf">downloadImage</span><span class="o">(</span><span class="n">uri</span><span class="o">);</span>
</span><span class="line"> <span class="o">}</span>
</span><span class="line">
</span><span class="line"> <span class="nd">@Override</span>
</span><span class="line"> <span class="kd">protected</span> <span class="kt">void</span> <span class="nf">onPostExecute</span><span class="o">(</span><span class="n">Bitmap</span> <span class="n">result</span><span class="o">)</span> <span class="o">{</span>
</span><span class="line"> <span class="n">ImageView</span> <span class="n">imageView</span> <span class="o">=</span> <span class="n">imageViewWeakReference</span><span class="o">.</span><span class="na">get</span><span class="o">();</span>
</span><span class="line"> <span class="k">if</span> <span class="o">(</span><span class="n">imageView</span> <span class="o">!=</span> <span class="kc">null</span><span class="o">)</span> <span class="o">{</span>
</span><span class="line"> <span class="n">imageView</span><span class="o">.</span><span class="na">setImageBitmap</span><span class="o">(</span><span class="n">result</span><span class="o">);</span>
</span><span class="line"> <span class="o">}</span>
</span><span class="line"> <span class="o">}</span>
</span><span class="line">
</span><span class="line"> <span class="kd">private</span> <span class="n">Bitmap</span> <span class="nf">downloadImage</span><span class="o">(</span><span class="n">Uri</span> <span class="n">url</span><span class="o">)</span> <span class="o">{</span>
</span><span class="line"> <span class="o">...</span>
</span><span class="line"> <span class="o">}</span>
</span><span class="line"><span class="o">}</span>
</span></code></pre></td></tr></table></div></figure></div>
<div class="section" id="lesson-ii-use-intentservice-to-run-business-logic">
<h2>Lesson II: Use IntentService to Run Business Logic</h2>
<p>AsyncTask是 Android 最常被用來處理複雜運算時用的工具，透過AsyncTask，我們可以在背景處裡
一些複雜的運算，再把結果放回前景之上。</p>
<p>但據我的經驗，使用 AsyncTask 同時間來擔任 MVC 中的 View & Controller 的工作，最後往往是
把程式碼弄成一團麵線。因此，在開發 Locadz SDK 時，我們把一些跟 UI 無關的運算，都切出來
變成 IntentService 或者是非 Inner class 的 AsyncTask ，把所有的運算邏輯從 Activity 中切出
來，增加重用的可能。</p>
<p>然後運算的結果，再透過 <a class="reference external" href="http://developer.android.com/reference/android/os/Handler.html#post(java.lang.Runnable)">getHandler().post(…)</a> 更新到 UI 之上.</p>
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</pre></td><td class="code"><pre><code class="java"><span class="line"><span class="cm">/** Service that retrieve the ad unit allocations from external source and cache locally in SharedPreference. */</span>
</span><span class="line"><span class="kd">public</span> <span class="kd">class</span> <span class="nc">AdUnitAllocationService</span> <span class="kd">extends</span> <span class="n">IntentService</span> <span class="o">{</span>
</span><span class="line">
</span><span class="line"> <span class="kd">private</span> <span class="kd">static</span> <span class="kd">final</span> <span class="kt">int</span> <span class="n">CACHE_EXPIRATION_PERIOD</span> <span class="o">=</span> <span class="mi">30</span> <span class="o">*</span> <span class="mi">60</span> <span class="o">*</span> <span class="mi">1000</span><span class="o">;</span> <span class="c1">// 30 minutes.</span>
</span><span class="line">
</span><span class="line"> <span class="kd">private</span> <span class="kd">final</span> <span class="kd">static</span> <span class="n">String</span> <span class="n">PREFS_STRING_TIMESTAMP</span> <span class="o">=</span> <span class="s">"timestamp"</span><span class="o">;</span>
</span><span class="line"> <span class="kd">private</span> <span class="kd">final</span> <span class="kd">static</span> <span class="n">String</span> <span class="n">PREFS_STRING_CONFIG</span> <span class="o">=</span> <span class="s">"config"</span><span class="o">;</span>
</span><span class="line">
</span><span class="line"> <span class="c1">// response code for possible result.</span>
</span><span class="line"> <span class="kd">public</span> <span class="kd">static</span> <span class="kd">final</span> <span class="kt">int</span> <span class="n">RESULT_OK</span> <span class="o">=</span> <span class="mi">1</span><span class="o">;</span>
</span><span class="line">
</span><span class="line"> <span class="kd">public</span> <span class="nf">AdUnitAllocationService</span><span class="o">()</span> <span class="o">{</span>
</span><span class="line"> <span class="kd">super</span><span class="o">(</span><span class="n">AdUnitAllocationService</span><span class="o">.</span><span class="na">class</span><span class="o">.</span><span class="na">getCanonicalName</span><span class="o">());</span>
</span><span class="line"> <span class="o">}</span>
</span><span class="line">
</span><span class="line"> <span class="nd">@Override</span>
</span><span class="line"> <span class="kd">protected</span> <span class="kt">void</span> <span class="nf">onHandleIntent</span><span class="o">(</span><span class="n">Intent</span> <span class="n">intent</span><span class="o">)</span> <span class="o">{</span>
</span><span class="line">
</span><span class="line"> <span class="n">AdUnitContext</span> <span class="n">adUnitContext</span> <span class="o">=</span>
</span><span class="line"> <span class="o">(</span><span class="n">AdUnitContext</span><span class="o">)</span> <span class="n">intent</span><span class="o">.</span><span class="na">getParcelableExtra</span><span class="o">(</span><span class="n">IntentConstants</span><span class="o">.</span><span class="na">EXTRA_ADUNIT_CONTEXT</span><span class="o">);</span>
</span><span class="line">
</span><span class="line"> <span class="n">AdUnitAllocation</span> <span class="n">adUnitAllocation</span> <span class="o">=</span> <span class="n">getAdUnitAllocation</span><span class="o">(</span><span class="n">adUnitContext</span><span class="o">);</span>
</span><span class="line">
</span><span class="line"> <span class="k">if</span> <span class="o">(</span><span class="n">adUnitAllocation</span> <span class="o">!=</span> <span class="kc">null</span><span class="o">)</span> <span class="o">{</span>
</span><span class="line"> <span class="n">Ration</span> <span class="n">ration</span> <span class="o">=</span> <span class="n">getRandomRation</span><span class="o">(</span><span class="n">adUnitAllocation</span><span class="o">.</span><span class="na">getRations</span><span class="o">());</span>
</span><span class="line">
</span><span class="line"> <span class="c1">// send response through ResultReceiver.</span>
</span><span class="line"> <span class="n">ResultReceiver</span> <span class="n">receiver</span> <span class="o">=</span> <span class="n">intent</span><span class="o">.</span><span class="na">getParcelableExtra</span><span class="o">(</span><span class="n">IntentConstants</span><span class="o">.</span><span class="na">EXTRA_RECEIVER</span><span class="o">);</span>
</span><span class="line">
</span><span class="line"> <span class="n">Bundle</span> <span class="n">resultData</span> <span class="o">=</span> <span class="k">new</span> <span class="n">Bundle</span><span class="o">();</span>
</span><span class="line"> <span class="n">resultData</span><span class="o">.</span><span class="na">putString</span><span class="o">(</span><span class="n">IntentConstants</span><span class="o">.</span><span class="na">EXTRA_ADUNIT_ID</span><span class="o">,</span> <span class="n">adUnitContext</span><span class="o">.</span><span class="na">getAdUnitId</span><span class="o">());</span>
</span><span class="line"> <span class="n">resultData</span><span class="o">.</span><span class="na">putSerializable</span><span class="o">(</span><span class="n">IntentConstants</span><span class="o">.</span><span class="na">EXTRA_RATION</span><span class="o">,</span> <span class="n">ration</span><span class="o">);</span>
</span><span class="line"> <span class="n">resultData</span><span class="o">.</span><span class="na">putSerializable</span><span class="o">(</span><span class="n">IntentConstants</span><span class="o">.</span><span class="na">EXTRA_EXTRA</span><span class="o">,</span>
</span><span class="line"> <span class="n">adUnitAllocation</span><span class="o">.</span><span class="na">getExtra</span><span class="o">());</span>
</span><span class="line">
</span><span class="line"> <span class="n">receiver</span><span class="o">.</span><span class="na">send</span><span class="o">(</span><span class="n">RESULT_OK</span><span class="o">,</span> <span class="n">resultData</span><span class="o">);</span>
</span><span class="line"> <span class="o">}</span>
</span><span class="line"> <span class="o">}</span>
</span><span class="line">
</span><span class="line"> <span class="cm">/**</span>
</span><span class="line"><span class="cm"> * Select a random ration form the provided rations.</span>
</span><span class="line"><span class="cm"> * @param rations the candidates.</span>
</span><span class="line"><span class="cm"> * @return a random ration from the candidates.</span>
</span><span class="line"><span class="cm"> */</span>
</span><span class="line"> <span class="kd">private</span> <span class="n">Ration</span> <span class="nf">getRandomRation</span><span class="o">(</span><span class="n">List</span><span class="o"><</span><span class="n">Ration</span><span class="o">></span> <span class="n">rations</span><span class="o">)</span> <span class="o">{</span>
</span><span class="line"> <span class="c1">//...</span>
</span><span class="line"> <span class="o">}</span>
</span><span class="line">
</span><span class="line"> <span class="cm">/**</span>
</span><span class="line"><span class="cm"> * Get the allocation configuration for the adunit.</span>
</span><span class="line"><span class="cm"> * @param adUnitContext the context of the adunit.</span>
</span><span class="line"><span class="cm"> * @return the allocation configuration for the adunit.</span>
</span><span class="line"><span class="cm"> */</span>
</span><span class="line"> <span class="n">AdUnitAllocation</span> <span class="nf">getAdUnitAllocation</span><span class="o">(</span><span class="n">AdUnitContext</span> <span class="n">adUnitContext</span><span class="o">)</span> <span class="o">{</span>
</span><span class="line"> <span class="c1">//...</span>
</span><span class="line"> <span class="o">}</span>
</span><span class="line"><span class="o">}</span>
</span></code></pre></td></tr></table></div></figure></div>
<div class="section" id="lesson-iii-use-disk-cache-instead-of-main-memory-cache">
<h2>Lesson III: Use Disk Cache instead of (Main) Memory Cache</h2>
<p>底下的圖表，是Jeff Dean發表的，在談的是讀取資料的的效率，我們把這幾個數字先記起來，
再加一個代表UI設計時人體覺得是即時反應的反應時間上限 100 ms。然後我們再來談 Android UI 的設計。</p>
<img alt="/images/2012-04-20/numbers-everyone-should-know.png" src="http://blog.locadz.com//images/2012-04-20/numbers-everyone-should-know.png" />
<p>大家可以看到 Main Memory Reference(0.001ms) 與 Disk Seek(10ms) Disk Read(30ms) 的重大差
距，然而，後者的數字在 Mobile Phone 上就不是這樣了。在 Mobile Phone 上，傳統的硬碟扮演的角色，
被NAND Flash Memory, External SD Card所取代了。在存取效率上 NAND Flash Memory 雖然不
比 RAM 快，但是，也仍是 seek time ~1ms 的狠角色。</p>
<p>這 1ms 的負擔，雖比 0.001ms 的負擔高上百倍，以上，但是在 100ms 這UI 反應需求上，卻又變得很渺小了。</p>
<p>因此，在這邊，我會建議大家，若是有 cache 的需求時，直接往 <a class="reference external" href="http://developer.android.com/guide/topics/data/data-storage.html#filesInternal">Internal Storage</a> 塞吧，不要放
在Main memory上，或用個SoftReferenceMap包著。</p>
</div>
<div class="section" id="lesson-iv-make-all-public-method-async-to-avoid-ui-update-issue">
<h2>Lesson IV: Make All Public Method Async to Avoid UI Update Issue</h2>
<p>在上面第一個範例中有個錯誤，那就是DownloadImagesTask.onPostExecute()會在呼叫DownloadImagesTask.execute(…)的
那個 Thread 上執行，如果說，很不幸的，這個 DownloadImagesTask 並不是從 UI Thread 上來呼叫的話，那
麼，imageView.setImageBitmap(result)便有可能不會即時更新到UI之上。</p>
<p>如果你的開發環境會有這種問題，在包在層層呼叫後，無法確保 Method 是否是在 UI Thread 上執行；那麼我
會建議你把會更新 UI 的 Method ，標成 protected ，然後開放一個 public async method 出來，範例如下：</p>
<figure class="code"><div class="highlight"><table><tr><td class="gutter"><pre class="line-numbers"><span class="line-number">1</span>
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</pre></td><td class="code"><pre><code class="java"><span class="line"><span class="cm">/**</span>
</span><span class="line"><span class="cm"> * Remove old ad views and push the new one.</span>
</span><span class="line"><span class="cm"> *</span>
</span><span class="line"><span class="cm"> * @param subView the adview to push.</span>
</span><span class="line"><span class="cm"> */</span>
</span><span class="line"><span class="kd">protected</span> <span class="kt">void</span> <span class="nf">pushSubView</span><span class="o">(</span><span class="n">ViewGroup</span> <span class="n">subView</span><span class="o">)</span> <span class="o">{</span>
</span><span class="line"> <span class="c1">//....</span>
</span><span class="line"><span class="o">}</span>
</span><span class="line">
</span><span class="line"><span class="cm">/**</span>
</span><span class="line"><span class="cm"> * submit a push view request to Android's handler. This will remove</span>
</span><span class="line"><span class="cm"> * old ad view and push a new one to this layout asynchronously.</span>
</span><span class="line"><span class="cm"> *</span>
</span><span class="line"><span class="cm"> * @param subView the adview to push.</span>
</span><span class="line"><span class="cm"> */</span>
</span><span class="line"><span class="kd">public</span> <span class="kt">void</span> <span class="nf">submitPushSubViewRequest</span><span class="o">(</span><span class="n">ViewGroup</span> <span class="n">subView</span><span class="o">)</span> <span class="o">{</span>
</span><span class="line"> <span class="n">Log</span><span class="o">.</span><span class="na">d</span><span class="o">(</span><span class="n">LOG_TAG</span><span class="o">,</span> <span class="n">String</span><span class="o">.</span><span class="na">format</span><span class="o">(</span><span class="s">"Scheduled pushSubView(%s)"</span><span class="o">,</span> <span class="n">subView</span><span class="o">));</span>
</span><span class="line"> <span class="n">getHandler</span><span class="o">().</span><span class="na">post</span><span class="o">(</span><span class="k">new</span> <span class="n">ViewAdRunnable</span><span class="o">(</span><span class="k">this</span><span class="o">,</span> <span class="n">subView</span><span class="o">));</span>
</span><span class="line"><span class="o">}</span>
</span><span class="line">
</span><span class="line">
</span><span class="line"><span class="cm">/**</span>
</span><span class="line"><span class="cm"> * Runnable runs on the Main Thread that pushes an AdView to the layout.</span>
</span><span class="line"><span class="cm"> */</span>
</span><span class="line"><span class="kd">private</span> <span class="kd">static</span> <span class="kd">final</span> <span class="kd">class</span> <span class="nc">ViewAdRunnable</span> <span class="kd">implements</span> <span class="n">Runnable</span> <span class="o">{</span>
</span><span class="line">
</span><span class="line"> <span class="kd">private</span> <span class="kd">final</span> <span class="n">WeakReference</span><span class="o"><</span><span class="n">Adunitlayout</span><span class="o">></span> <span class="n">locadzLayoutWeakReference</span><span class="o">;</span>
</span><span class="line">
</span><span class="line"> <span class="kd">private</span> <span class="n">ViewGroup</span> <span class="n">subView</span><span class="o">;</span>
</span><span class="line">
</span><span class="line"> <span class="kd">public</span> <span class="nf">ViewAdRunnable</span><span class="o">(</span><span class="n">AdUnitLayout</span> <span class="n">layout</span><span class="o">,</span> <span class="n">ViewGroup</span> <span class="n">subView</span><span class="o">)</span> <span class="o">{</span>
</span><span class="line"> <span class="n">locadzLayoutWeakReference</span> <span class="o">=</span> <span class="k">new</span> <span class="n">WeakReference</span><span class="o"><</span><span class="n">Adunitlayout</span><span class="o">>(</span><span class="n">layout</span><span class="o">);</span>
</span><span class="line"> <span class="k">this</span><span class="o">.</span><span class="na">subView</span> <span class="o">=</span> <span class="n">subView</span><span class="o">;</span>
</span><span class="line"> <span class="o">}</span>
</span><span class="line">
</span><span class="line"> <span class="nd">@Override</span>
</span><span class="line"> <span class="kd">public</span> <span class="kt">void</span> <span class="nf">run</span><span class="o">()</span> <span class="o">{</span>
</span><span class="line"> <span class="n">AdUnitLayout</span> <span class="n">locadzLayout</span> <span class="o">=</span> <span class="n">locadzLayoutWeakReference</span><span class="o">.</span><span class="na">get</span><span class="o">();</span>
</span><span class="line"> <span class="k">if</span> <span class="o">(</span><span class="n">locadzLayout</span> <span class="o">!=</span> <span class="kc">null</span><span class="o">)</span> <span class="o">{</span>
</span><span class="line"> <span class="n">locadzLayout</span><span class="o">.</span><span class="na">pushSubView</span><span class="o">(</span><span class="n">subView</span><span class="o">);</span>
</span><span class="line"> <span class="o">}</span>
</span><span class="line"> <span class="o">}</span>
</span><span class="line"><span class="o">}</span>
</span></code></pre></td></tr></table></div></figure></div>]]></content>
</entry>
</feed>