Mikel
[转载]安卓开发笔记——关于AsyncTask的使用 – Balla_兔子 – 博客园.
在安卓开发中，我们经常要进行一些耗时操作，比如数据库操作，获取网络资源，读取内存文件等等，当我们在处理这些耗时操作的时候，如果我们直接在 UI主线程进行，那么可能会导致阻塞UI主线程，使得UI界面卡顿，带来很不好的用户体验，因此安卓也给我们提供了2个异步操作的类，Handler和 AsyncTask。
今天先讲AsyncTask，AsyncTask类是Andorid提供给我们的一个轻量级异步类，算是一个框架，它对线程之间的通讯进行了封装，并且提供了简易的编程操作，使得我们可以很轻松的实现后台线程和UI主线程之间的通讯。
我写了一个异步获取网络图片的小例子，先来看实现效果：
以上是官网对AsyncTask的一些描述，大致意思是：
AsyncTask是一个易操作线程使用类，它可以帮助我们把后台线程处理程序的结果发送给UI主线程，使UI线程得到更新。
AsyncTask类提供了3个泛型参数（Params，Progress，Result）和4个执行步骤（下文会具体提及）
先来看下3个泛型参数
1、Params：这是一个任务参数，一般我们会定义成String类型的，例如本例子中要获取网络资源的URL地址
2、Progress：任务执行的刻度，一般我们会定义成Integer类型
3、Result：返回结果类型，例如本例中是对网络图片进行获取，那么它的返回类型应该是BitMap
再来看下4个步骤：
当我们的类去实现AsyncTask类的时候至少需要实现doInBackground(Params…)方法，这里作为学习，我把每一个的具体工作任务也说说
它的执行顺序是这样的 onPreExecute–>doInBackground–>onProgressUpdate–>onPostExecute
1、onPreExecute：这是一个预处理方法，在任务开始的时候执行，我们可以在这里进行一些控件的实例化，设置属性等。（非必须）
2、doInBackground：这是一个任务操作方法，也是最重要的一个方法，所有的耗时操作都应该在这里执行。（必须）
3、onProgressUpdate：这是一个进度即时更新方法，在这里我们可以即时更新任务滚动条的进度。（非必须，当在doInBackground里调用publishProgress时触发）
4、onPostExecute：这是一个任务结果处理方法，在doInBackground里执行完任务，会将结果通知给这个类，在这类中我们可以对UI进行更新操作（非必须）
上面的1、3、4是UI主线程触发调用的，所以可以对UI进行更新操作，而第2步是个异步操作，不能在里面进行UI的更新操作。
关于AsyncTask的调用，其实非常简单，我们在AsyncTask类被继承实现的时候，在主线程直接对其对象调用execute(Params..)方法即可。
好了，文字介绍到此结束，上代码：
1、布局文件
<span class="pln"></span><span class="pun">&</span><span class="pln">nbsp</span><span class="pun">;</span><span class="pln"></span><span class="pun">&</span><span class="pln">nbsp</span><span class="pun">;</span><span class="pln"></span> |
2、AsyncTask的实现类
<span class="kwd">package</span><span class="pln"> com</span><span class="pun">.</span><span class="pln">example</span><span class="pun">.</span><span class="pln">asynctasktest</span><span class="pun">;</span><span class="pln"></span><span class="kwd">import</span><span class="pln"> java</span><span class="pun">.</span><span class="pln">io</span><span class="pun">.</span><span class="typ">ByteArrayOutputStream</span><span class="pun">;</span><span class="pln"></span><span class="kwd">import</span><span class="pln"> java</span><span class="pun">.</span><span class="pln">io</span><span class="pun">.</span><span class="typ">IOException</span><span class="pun">;</span><span class="pln"></span><span class="kwd">import</span><span class="pln"> java</span><span class="pun">.</span><span class="pln">io</span><span class="pun">.</span><span class="typ">InputStream</span><span class="pun">;</span><span class="pln"></span><span class="kwd">import</span><span class="pln"> java</span><span class="pun">.</span><span class="pln">io</span><span class="pun">.</span><span class="typ">OutputStream</span><span class="pun">;</span><span class="pln"></span><span class="kwd">import</span><span class="pln"> org</span><span class="pun">.</span><span class="pln">apache</span><span class="pun">.</span><span class="pln">http</span><span class="pun">.</span><span class="typ">HttpResponse</span><span class="pun">;</span><span class="pln"></span><span class="kwd">import</span><span class="pln"> org</span><span class="pun">.</span><span class="pln">apache</span><span class="pun">.</span><span class="pln">http</span><span class="pun">.</span><span class="pln">client</span><span class="pun">.</span><span class="typ">ClientProtocolException</span><span class="pun">;</span><span class="pln"></span><span class="kwd">import</span><span class="pln"> org</span><span class="pun">.</span><span class="pln">apache</span><span class="pun">.</span><span class="pln">http</span><span class="pun">.</span><span class="pln">client</span><span class="pun">.</span><span class="typ">HttpClient</span><span class="pun">;</span><span class="pln"></span><span class="kwd">import</span><span class="pln"> org</span><span class="pun">.</span><span class="pln">apache</span><span class="pun">.</span><span class="pln">http</span><span class="pun">.</span><span class="pln">client</span><span class="pun">.</span><span class="pln">methods</span><span class="pun">.</span><span class="typ">HttpGet</span><span class="pun">;</span><span class="pln"></span><span class="kwd">import</span><span class="pln"> org</span><span class="pun">.</span><span class="pln">apache</span><span class="pun">.</span><span class="pln">http</span><span class="pun">.</span><span class="pln">impl</span><span class="pun">.</span><span class="pln">client</span><span class="pun">.</span><span class="typ">DefaultHttpClient</span><span class="pun">;</span><span class="pln"></span><span class="kwd">import</span><span class="pln"> android</span><span class="pun">.</span><span class="pln">app</span><span class="pun">.</span><span class="typ">ProgressDialog</span><span class="pun">;</span><span class="pln"></span><span class="kwd">import</span><span class="pln"> android</span><span class="pun">.</span><span class="pln">graphics</span><span class="pun">.</span><span class="typ">Bitmap</span><span class="pun">;</span><span class="pln"></span><span class="kwd">import</span><span class="pln"> android</span><span class="pun">.</span><span class="pln">graphics</span><span class="pun">.</span><span class="typ">BitmapFactory</span><span class="pun">;</span><span class="pln"></span><span class="kwd">import</span><span class="pln"> android</span><span class="pun">.</span><span class="pln">os</span><span class="pun">.</span><span class="typ">AsyncTask</span><span class="pun">;</span><span class="pln"></span><span class="kwd">import</span><span class="pln"> android</span><span class="pun">.</span><span class="pln">widget</span><span class="pun">.</span><span class="typ">ImageView</span><span class="pun">;</span><span class="pln"></span><span class="kwd">public</span><span class="pln"> </span><span class="kwd">class</span><span class="pln"> </span><span class="typ">MyAsyncTask</span><span class="pln"> </span><span class="kwd">extends</span><span class="pln"> </span><span class="typ">AsyncTask</span><span class="pun">&</span><span class="pln">lt</span><span class="pun">;</span><span class="typ">String</span><span class="pun">,</span><span class="pln"> </span><span class="typ">Integer</span><span class="pun">,</span><span class="pln"> </span><span class="typ">Bitmap</span><span class="pun">&</span><span class="pln">gt</span><span class="pun">;</span><span class="pln"> </span><span class="pun">{</span><span class="pln"></span><span class="kwd">private</span><span class="pln"> </span><span class="typ">ImageView</span><span class="pln"> imageView</span><span class="pun">;</span><span class="pln"></span><span class="kwd">private</span><span class="pln"> </span><span class="typ">ProgressDialog</span><span class="pln"> progressDialog</span><span class="pun">;</span><span class="pln"></span><span class="kwd">public</span><span class="pln"> </span><span class="typ">MyAsyncTask</span><span class="pun">(</span><span class="typ">ImageView</span><span class="pln"> imageView</span><span class="pun">,</span><span class="pln"> </span><span class="typ">ProgressDialog</span><span class="pln"> progressDialog</span><span class="pun">)</span><span class="pln"> </span><span class="pun">{</span><span class="pln"></span><span class="kwd">this</span><span class="pun">.</span><span class="pln">imageView </span><span class="pun">=</span><span class="pln"> imageView</span><span class="pun">;</span><span class="pln"></span><span class="kwd">this</span><span class="pun">.</span><span class="pln">progressDialog </span><span class="pun">=</span><span class="pln"> progressDialog</span><span class="pun">;</span><span class="pln"></span><span class="pun">}</span><span class="pln"></span><span class="com">/*** 执行第一步 这里为预处理操作，被UI线程所调用（可以在这里完成进度条的属性设置）*/</span><span class="pln"></span><span class="lit">@Override</span><span class="pln"></span><span class="kwd">protected</span><span class="pln"> </span><span class="kwd">void</span><span class="pln"> onPreExecute</span><span class="pun">()</span><span class="pln"> </span><span class="pun">{</span><span class="pln"></span><span class="kwd">super</span><span class="pun">.</span><span class="pln">onPreExecute</span><span class="pun">();</span><span class="pln">progressDialog</span><span class="pun">.</span><span class="pln">setTitle</span><span class="pun">(</span><span class="str">"当前任务"</span><span class="pun">);</span><span class="pln">progressDialog</span><span class="pun">.</span><span class="pln">setMessage</span><span class="pun">(</span><span class="str">"正在下载图片，请稍后..."</span><span class="pun">);</span><span class="pln">progressDialog</span><span class="pun">.</span><span class="pln">setProgressStyle</span><span class="pun">(</span><span class="typ">ProgressDialog</span><span class="pun">.</span><span class="pln">STYLE_HORIZONTAL</span><span class="pun">);</span><span class="com">//设置进度条样式，横项</span><span class="pln">progressDialog</span><span class="pun">.</span><span class="pln">show</span><span class="pun">();</span><span class="pln"></span><span class="pun">}</span><span class="pln"></span><span class="com">/*** 执行第二步 这里为异步线程，在这里处理耗时任务操作(比如：下载，读取文件)* 通过调用publishProgress方法（传递即时任务进度）可以触发onProgressUpdate的执行*/</span><span class="pln"></span><span class="lit">@Override</span><span class="pln"></span><span class="kwd">protected</span><span class="pln"> </span><span class="typ">Bitmap</span><span class="pln"> doInBackground</span><span class="pun">(</span><span class="typ">String</span><span class="pun">...</span><span class="pln"> </span><span class="kwd">params</span><span class="pun">)</span><span class="pln"> </span><span class="pun">{</span><span class="pln"></span><span class="typ">String</span><span class="pln"> path</span><span class="pun">=</span><span class="kwd">params</span><span class="pun">[</span><span class="lit">0</span><span class="pun">];</span><span class="pln"></span><span class="typ">Bitmap</span><span class="pln"> bitmap</span><span class="pun">=</span><span class="kwd">null</span><span class="pun">;</span><span class="pln"></span><span class="typ">HttpClient</span><span class="pln"> httpClient</span><span class="pun">=</span><span class="kwd">new</span><span class="pln"> </span><span class="typ">DefaultHttpClient</span><span class="pun">();</span><span class="pln"></span><span class="typ">HttpGet</span><span class="pln"> httpGet</span><span class="pun">=</span><span class="kwd">new</span><span class="pln"> </span><span class="typ">HttpGet</span><span class="pun">(</span><span class="pln">path</span><span class="pun">);</span><span class="pln"></span><span class="typ">InputStream</span><span class="pln"> inputStream</span><span class="pun">=</span><span class="kwd">null</span><span class="pun">;</span><span class="pln"></span><span class="kwd">try</span><span class="pln"> </span><span class="pun">{</span><span class="pln"></span><span class="typ">HttpResponse</span><span class="pln"> httpResponse</span><span class="pun">=</span><span class="pln">httpClient</span><span class="pun">.</span><span class="pln">execute</span><span class="pun">(</span><span class="pln">httpGet</span><span class="pun">);</span><span class="pln"></span><span class="kwd">if</span><span class="pun">(</span><span class="pln">httpResponse</span><span class="pun">.</span><span class="pln">getStatusLine</span><span class="pun">().</span><span class="pln">getStatusCode</span><span class="pun">()==</span><span class="lit">200</span><span class="pun">){</span><span class="pln"></span><span class="com">//连接成功</span><span class="pln"></span><span class="com">// HttpEntity entity=httpResponse.getEntity();</span><span class="pln"></span><span class="com">// byte[] data=EntityUtils.toByteArray(entity);</span><span class="pln"></span><span class="com">// bitmap=BitmapFactory.decodeByteArray(data, 0, data.length);</span><span class="pln">inputStream</span><span class="pun">=</span><span class="pln">httpResponse</span><span class="pun">.</span><span class="pln">getEntity</span><span class="pun">().</span><span class="pln">getContent</span><span class="pun">();</span><span class="pln"></span><span class="typ">ByteArrayOutputStream</span><span class="pln"> outputStream</span><span class="pun">=</span><span class="kwd">new</span><span class="pln"> </span><span class="typ">ByteArrayOutputStream</span><span class="pun">();</span><span class="pln"></span><span class="kwd">long</span><span class="pln"> fileSize</span><span class="pun">=</span><span class="pln">httpResponse</span><span class="pun">.</span><span class="pln">getEntity</span><span class="pun">().</span><span class="pln">getContentLength</span><span class="pun">();</span><span class="com">//文件总大小</span><span class="pln"></span><span class="kwd">byte</span><span class="pun">[]</span><span class="pln"> data</span><span class="pun">=</span><span class="kwd">new</span><span class="pln"> </span><span class="kwd">byte</span><span class="pun">[</span><span class="lit">1024</span><span class="pun">];</span><span class="com">//每次读取的大小</span><span class="pln"></span><span class="kwd">int</span><span class="pln"> len</span><span class="pun">=</span><span class="lit">0</span><span class="pun">;</span><span class="com">//本次读取的大小</span><span class="pln"></span><span class="kwd">int</span><span class="pln"> total</span><span class="pun">=</span><span class="lit">0</span><span class="pun">;</span><span class="com">//累计读取的大小</span><span class="pln"></span><span class="kwd">while</span><span class="pun">((</span><span class="pln">len</span><span class="pun">=</span><span class="pln">inputStream</span><span class="pun">.</span><span class="pln">read</span><span class="pun">(</span><span class="pln">data</span><span class="pun">))!=-</span><span class="lit">1</span><span class="pun">){</span><span class="pln">total</span><span class="pun">+=</span><span class="pln">len</span><span class="pun">;</span><span class="com">//累计读取的大小</span><span class="pln"></span><span class="kwd">int</span><span class="pln"> values</span><span class="pun">=(</span><span class="kwd">int</span><span class="pun">)</span><span class="pln"> </span><span class="pun">((</span><span class="pln">total</span><span class="pun">/(</span><span class="kwd">float</span><span class="pun">)</span><span class="pln">fileSize</span><span class="pun">)*</span><span class="lit">100</span><span class="pun">);</span><span class="com">//得到当前任务进行百分比</span><span class="pln">publishProgress</span><span class="pun">(</span><span class="pln">values</span><span class="pun">);</span><span class="com">//触发onProgressUpdate更新即时进度</span><span class="pln">outputStream</span><span class="pun">.</span><span class="pln">write</span><span class="pun">(</span><span class="pln">data</span><span class="pun">,</span><span class="pln"> </span><span class="lit">0</span><span class="pun">,</span><span class="pln"> len</span><span class="pun">);</span><span class="pln"></span><span class="pun">}</span><span class="pln"></span><span class="kwd">byte</span><span class="pun">[]</span><span class="pln"> result</span><span class="pun">=</span><span class="pln">outputStream</span><span class="pun">.</span><span class="pln">toByteArray</span><span class="pun">();</span><span class="com">//转换为字节数组</span><span class="pln">bitmap</span><span class="pun">=</span><span class="typ">BitmapFactory</span><span class="pun">.</span><span class="pln">decodeByteArray</span><span class="pun">(</span><span class="pln">result</span><span class="pun">,</span><span class="pln"> </span><span class="lit">0</span><span class="pun">,</span><span class="pln"> result</span><span class="pun">.</span><span class="pln">length</span><span class="pun">);</span><span class="pln"></span><span class="pun">}</span><span class="pln"></span><span class="pun">}</span><span class="pln"> </span><span class="kwd">catch</span><span class="pln"> </span><span class="pun">(</span><span class="typ">ClientProtocolException</span><span class="pln"> e</span><span class="pun">)</span><span class="pln"> </span><span class="pun">{</span><span class="pln">e</span><span class="pun">.</span><span class="pln">printStackTrace</span><span class="pun">();</span><span class="pln"></span><span class="pun">}</span><span class="pln"> </span><span class="kwd">catch</span><span class="pln"> </span><span class="pun">(</span><span class="typ">IOException</span><span class="pln"> e</span><span class="pun">)</span><span class="pln"> </span><span class="pun">{</span><span class="pln">e</span><span class="pun">.</span><span class="pln">printStackTrace</span><span class="pun">();</span><span class="pln"></span><span class="pun">}</span><span class="kwd">finally</span><span class="pun">{</span><span class="pln"></span><span class="kwd">if</span><span class="pun">(</span><span class="pln">inputStream</span><span class="pun">!=</span><span class="kwd">null</span><span class="pun">){</span><span class="pln"></span><span class="kwd">try</span><span class="pln"> </span><span class="pun">{</span><span class="pln">inputStream</span><span class="pun">.</span><span class="pln">close</span><span class="pun">();</span><span class="pln"></span><span class="pun">}</span><span class="pln"> </span><span class="kwd">catch</span><span class="pln"> </span><span class="pun">(</span><span class="typ">IOException</span><span class="pln"> e</span><span class="pun">)</span><span class="pln"> </span><span class="pun">{</span><span class="pln">e</span><span class="pun">.</span><span class="pln">printStackTrace</span><span class="pun">();</span><span class="pln"></span><span class="pun">}</span><span class="pln"></span><span class="pun">}</span><span class="pln"></span><span class="pun">}</span><span class="pln"></span><span class="kwd">return</span><span class="pln"> bitmap</span><span class="pun">;</span><span class="pln"></span><span class="pun">}</span><span class="pln"></span><span class="com">/*** 执行第三步 这里为实时UI更新操作，被UI线程所调用 在这里可以即时更新（如进度条进度）*/</span><span class="pln"></span><span class="lit">@Override</span><span class="pln"></span><span class="kwd">protected</span><span class="pln"> </span><span class="kwd">void</span><span class="pln"> onProgressUpdate</span><span class="pun">(</span><span class="typ">Integer</span><span class="pun">...</span><span class="pln"> values</span><span class="pun">)</span><span class="pln"> </span><span class="pun">{</span><span class="pln"></span><span class="kwd">super</span><span class="pun">.</span><span class="pln">onProgressUpdate</span><span class="pun">(</span><span class="pln">values</span><span class="pun">);</span><span class="pln">progressDialog</span><span class="pun">.</span><span class="pln">setProgress</span><span class="pun">(</span><span class="pln">values</span><span class="pun">[</span><span class="lit">0</span><span class="pun">]);</span><span class="pln"></span><span class="pun">}</span><span class="pln"></span><span class="com">/*** 执行第四步 在这里会返回doInBackground的操作结果，被UI线程调用，更新最后UI结果*/</span><span class="pln"></span><span class="lit">@Override</span><span class="pln"></span><span class="kwd">protected</span><span class="pln"> </span><span class="kwd">void</span><span class="pln"> onPostExecute</span><span class="pun">(</span><span class="typ">Bitmap</span><span class="pln"> result</span><span class="pun">)</span><span class="pln"> </span><span class="pun">{</span><span class="pln"></span><span class="kwd">super</span><span class="pun">.</span><span class="pln">onPostExecute</span><span class="pun">(</span><span class="pln">result</span><span class="pun">);</span><span class="pln">progressDialog</span><span class="pun">.</span><span class="pln">dismiss</span><span class="pun">();</span><span class="pln">imageView</span><span class="pun">.</span><span class="pln">setImageBitmap</span><span class="pun">(</span><span class="pln">result</span><span class="pun">);</span><span class="pln"></span><span class="pun">}</span><span class="pln"></span><span class="pun">}</span> |
3、主类
<span class="kwd">package</span><span class="pln"> com</span><span class="pun">.</span><span class="pln">example</span><span class="pun">.</span><span class="pln">asynctasktest</span><span class="pun">;</span><span class="pln"></span><span class="kwd">import</span><span class="pln"> android</span><span class="pun">.</span><span class="pln">app</span><span class="pun">.</span><span class="typ">ProgressDialog</span><span class="pun">;</span><span class="pln"></span><span class="kwd">import</span><span class="pln"> android</span><span class="pun">.</span><span class="pln">os</span><span class="pun">.</span><span class="typ">Bundle</span><span class="pun">;</span><span class="pln"></span><span class="kwd">import</span><span class="pln"> android</span><span class="pun">.</span><span class="pln">support</span><span class="pun">.</span><span class="pln">v7</span><span class="pun">.</span><span class="pln">app</span><span class="pun">.</span><span class="typ">ActionBarActivity</span><span class="pun">;</span><span class="pln"></span><span class="kwd">import</span><span class="pln"> android</span><span class="pun">.</span><span class="pln">view</span><span class="pun">.</span><span class="typ">View</span><span class="pun">;</span><span class="pln"></span><span class="kwd">import</span><span class="pln"> android</span><span class="pun">.</span><span class="pln">view</span><span class="pun">.</span><span class="typ">View</span><span class="pun">.</span><span class="typ">OnClickListener</span><span class="pun">;</span><span class="pln"></span><span class="kwd">import</span><span class="pln"> android</span><span class="pun">.</span><span class="pln">widget</span><span class="pun">.</span><span class="typ">Button</span><span class="pun">;</span><span class="pln"></span><span class="kwd">import</span><span class="pln"> android</span><span class="pun">.</span><span class="pln">widget</span><span class="pun">.</span><span class="typ">ImageView</span><span class="pun">;</span><span class="pln"></span><span class="kwd">public</span><span class="pln"> </span><span class="kwd">class</span><span class="pln"> </span><span class="typ">MainActivity</span><span class="pln"> </span><span class="kwd">extends</span><span class="pln"> </span><span class="typ">ActionBarActivity</span><span class="pln"> </span><span class="pun">{</span><span class="pln"></span><span class="kwd">private</span><span class="pln"> </span><span class="typ">ImageView</span><span class="pln"> imageView</span><span class="pun">;</span><span class="pln"></span><span class="kwd">private</span><span class="pln"> </span><span class="typ">Button</span><span class="pln"> bt_download</span><span class="pun">;</span><span class="pln"></span><span class="kwd">private</span><span class="pln"> </span><span class="typ">ProgressDialog</span><span class="pln"> progressDialog</span><span class="pun">;</span><span class="com">//进度对话框</span><span class="pln"></span><span class="kwd">private</span><span class="pln"> </span><span class="typ">String</span><span class="pln"> path</span><span class="pun">=</span><span class="str">"http://img.pconline.com.cn/images/photoblog/5/3/7/5/5375781/20096/6/1244302842840.jpg"</span><span class="pun">;</span><span class="com">//下载图片路径</span><span class="pln"></span><span class="lit">@Override</span><span class="pln"></span><span class="kwd">protected</span><span class="pln"> </span><span class="kwd">void</span><span class="pln"> onCreate</span><span class="pun">(</span><span class="typ">Bundle</span><span class="pln"> savedInstanceState</span><span class="pun">)</span><span class="pln"> </span><span class="pun">{</span><span class="pln"></span><span class="kwd">super</span><span class="pun">.</span><span class="pln">onCreate</span><span class="pun">(</span><span class="pln">savedInstanceState</span><span class="pun">);</span><span class="pln">setContentView</span><span class="pun">(</span><span class="pln">R</span><span class="pun">.</span><span class="pln">layout</span><span class="pun">.</span><span class="pln">activity_main</span><span class="pun">);</span><span class="pln">imageView</span><span class="pun">=(</span><span class="typ">ImageView</span><span class="pun">)</span><span class="pln"> findViewById</span><span class="pun">(</span><span class="pln">R</span><span class="pun">.</span><span class="pln">id</span><span class="pun">.</span><span class="pln">imageView</span><span class="pun">);</span><span class="pln">bt_download</span><span class="pun">=(</span><span class="typ">Button</span><span class="pun">)</span><span class="pln"> findViewById</span><span class="pun">(</span><span class="pln">R</span><span class="pun">.</span><span class="pln">id</span><span class="pun">.</span><span class="pln">bt_download</span><span class="pun">);</span><span class="pln">progressDialog</span><span class="pun">=</span><span class="kwd">new</span><span class="pln"> </span><span class="typ">ProgressDialog</span><span class="pun">(</span><span class="kwd">this</span><span class="pun">);</span><span class="pln">bt_download</span><span class="pun">.</span><span class="pln">setOnClickListener</span><span class="pun">(</span><span class="kwd">new</span><span class="pln"> </span><span class="typ">OnClickListener</span><span class="pun">()</span><span class="pln"> </span><span class="pun">{</span><span class="pln"></span><span class="lit">@Override</span><span class="pln"></span><span class="kwd">public</span><span class="pln"> </span><span class="kwd">void</span><span class="pln"> onClick</span><span class="pun">(</span><span class="typ">View</span><span class="pln"> v</span><span class="pun">)</span><span class="pln"> </span><span class="pun">{</span><span class="pln"></span><span class="typ">MyAsyncTask</span><span class="pln"> myAsyncTask</span><span class="pun">=</span><span class="kwd">new</span><span class="pln"> </span><span class="typ">MyAsyncTask</span><span class="pun">(</span><span class="pln">imageView</span><span class="pun">,</span><span class="pln">progressDialog</span><span class="pun">);</span><span class="pln">myAsyncTask</span><span class="pun">.</span><span class="pln">execute</span><span class="pun">(</span><span class="pln">path</span><span class="pun">);</span><span class="pln"></span><span class="pun">}</span><span class="pln"></span><span class="pun">});</span><span class="pln"></span><span class="pun">}</span><span class="pln"></span><span class="pun">}</span> |
代码到此结束，注释很详细应该很好理解。
使用AsyncTask类，以下是几条必须遵守的准则：
- Task的实例必须在UI主线程中创建。
- execute方法必须在UI主线程中调用。
- 不要手动的调用onPreExecute(),onPostExecute(Result)，doInBackground(Params…), onProgressUpdate(Progress…)这几个方法。
- 该task只能被执行一次，否则多次调用时将会出现异常。
当然AsyncTask类不止这些东西，还有线程池的概念，今天先不讲，过几天连同Handler一起说。
对于简单的异步操作，掌握这些已经够了。
项目代码：http://pan.baidu.com/s/1kTkTgm7
作者：Balla_兔子
出处：http://www.cnblogs.com/lichenwei/
本文版权归作者和博客园共有,欢迎转载,但未经作者同意必须保留此段声明,且在文章页面明显位置给出原文链接。
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