NSOperation,NSOperationQueue,多线程,Concurrency, programming

一、Operation Queues简介

Cocoa operations 为我们提供了一种面向对象的方式的来封装异步任务。包含Cocoa框架中的NSOperation和NSOperationQueue两个类，Operation通常与OperationQueue相结合来使用，是多线程的一种实现方式。其实现方式一是创建新线程，二是使用GCD的方式实现，相对于GCD可操作性高，是GCD的一种替代方式。

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android,, qq,, receiver

QQ5.0 for Android发布一段时间了，UI交互大调整，感受了一下很不习惯。不过新增了一个很赞的功能，当手机处于锁屏状态是有新消息提示时会在桌面显示一个消息框，并且可以直接回复信息，真的很方便。于是试着自己实现该功能。仔细想了想，大致思路如下：

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SwipeRefreshLayout,LoadMoreListView,android,listview

Google自己的下拉刷新组件SwipeRefreshLayout非常nice。和LoadMoreListView结合使用，可以非常容易的实现常用的下拉刷新和上拉加载更多功能。以下是一个简单的Demo。

布局如下: 

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<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
      xmlns:tools="http://schemas.android.com/tools"
          android:id="@+id/container"
      android:layout_width="match_parent"
        android:layout_height="match_parent"
      tools:context="com.cloay.stunningrefreshloadmoredemo.MainActivity"
      tools:ignore="MergeRootFrame" >
          <android.support.v4.widget.SwipeRefreshLayout
      android:id="@+id/swipe_refresh"
          android:layout_width="match_parent"
          android:layout_height="match_parent" >

            <com.cloay.stunningrefreshloadmoredemo.widgets.LoadMoreListView
                 android:id="@+id/listview"
               android:layout_width="match_parent"
               android:layout_height="match_parent" >
      </com.cloay.stunningrefreshloadmoredemo.widgets.LoadMoreListView>
    </android.support.v4.widget.SwipeRefreshLayout>
</FrameLayout>

主要代码

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public class MainActivity extends ActionBarActivity implements OnRefreshListener, OnLoadMoreListener{

    private SwipeRefreshLayout swipeLayout;
    private LoadMoreListView listView;
    private MyAdapter adapter;

  @Override
  protected void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.activity_main);

      swipeLayout = (SwipeRefreshLayout) this.findViewById(R.id.swipe_refresh);
        swipeLayout.setOnRefreshListener(this);

        // set style  
        swipeLayout.setColorScheme(android.R.color.holo_red_light, android.R.color.holo_green_light,
                android.R.color.holo_blue_bright, android.R.color.holo_orange_light);
        listView = (LoadMoreListView) this.findViewById(R.id.listview);
        listView.setOnLoadMoreListener(this);
        adapter = new MyAdapter();
        listView.setAdapter(adapter);
  }

  @Override
  public void onRefresh() {
      new AsyncTask<Void, Void, Void>() {

          @Override
          protected Void doInBackground(Void... params) {
              try {
                  Thread.sleep(3*1000); //sleep 3 seconds
              } catch (InterruptedException e) {
                  e.printStackTrace();
              }
              return null;
          }

          @Override
          protected void onPostExecute(Void result) {
              adapter.count = 15;
              adapter.notifyDataSetChanged();
              swipeLayout.setRefreshing(false);
              listView.setCanLoadMore(adapter.count < 45);
              super.onPostExecute(result);
          }

      }.execute();
  }

  @Override
  public void onLoadMore() {

      new AsyncTask<Void, Void, Void>() {

          @Override
          protected Void doInBackground(Void... params) {
              try {
                  Thread.sleep(3*1000);    //sleep 3 seconds
              } catch (InterruptedException e) {
                  e.printStackTrace();
              }
              return null;
          }

          @Override
          protected void onPostExecute(Void result) {
              adapter.count += 15;
              adapter.notifyDataSetChanged();
              listView.setCanLoadMore(adapter.count < 45);
              listView.onLoadMoreComplete();
              super.onPostExecute(result);
          }

      }.execute();
  }


  private class MyAdapter extends BaseAdapter{
      public int count = 15;
      @Override
      public int getCount() {
          return count;
      }

      @Override
      public Object getItem(int position) {
          return null;
      }

      @Override
      public long getItemId(int position) {
          return 0;
      }

      @Override
      public View getView(int position, View convertView, ViewGroup parent) {
          ViewHolder holder = null;
          if (convertView == null) {
              holder = new ViewHolder();
              convertView = LayoutInflater.from(MainActivity.this).inflate(android.R.layout.simple_list_item_1, null);
              holder.textV = (TextView) convertView.findViewById(android.R.id.text1);
              convertView.setTag(holder);
          }else{
              holder = (ViewHolder) convertView.getTag();
          }
          holder.textV.setText("This is " + (position + 1) + " line.");
          return convertView;
      }

      private class ViewHolder{
          TextView textV;
      }

  }

}

效果还不错，小伙伴可以试试哦！Demo已上传Github: StunningPullRefreshAndLoadMoreDemo