Android下拉刷新以及GridView使用方法详解

GridView是类似于ListView的控件，只是GridView可以使用多个列来呈现内容，而ListView是以行为单位，所以用法上是差不多的。
主布局文件，因为要做下拉刷新，所以加了一个ProgressBar，GridView的numColumns属性是指每一行有多少列

 <RelativeLayout xmlns:Android="Http://schemas.android.com/apk/res/android"
  xmlns:tools="http://schemas.android.com/tools"
  android:layout_width="match_parent"
  android:layout_height="match_parent"
  tools:context="com.example.girdlayoutdemo.MainActivity" >
  <ProgressBar
    android:id="@+id/pb"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_centerHorizontal="true" />
  <GridView
    android:layout_below="@id/pb"
    android:id="@+id/gv"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:layout_margin="5dp"
    android:gravity="center"
    android:numColumns="2" >
  </GridView>
</RelativeLayout>

每个Item的布局文件，这里比较简单的一张图片加一段文字

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
  android:layout_width="match_parent"
  android:layout_height="match_parent"
  android:orientation="vertical" >
  <ImageView
    android:id="@+id/item_iv"
    android:layout_width="fill_parent"
    android:layout_height="0dp"
    android:layout_weight="3" />
  <TextView
    android:id="@+id/item_tv"
    android:layout_width="match_parent"
    android:layout_height="0dp"
    android:layout_weight="1" />
</LinearLayout>

主活动代码：

public class MainActivity extends Activity {
  private GridView gv;
  private ProgressBar pb;
  private List<Map<String, Object>> list;
  private SimpleAdapter adapter;
  private GestureDetector gsDetector;
  private Handler handler = new Handler() {
    @Override
    public void handleMessage(Message msg) {
      switch (msg.what) {
      case 1:
        pb.setVisibility(View.GoNE);
        Toast.makeText(MainActivity.this, "刷新成功", 200).show();
        break;
      default:
        break;
      }
    }
  };
  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    pb = (ProgressBar) findViewById(R.id.pb);
    gv = (GridView) findViewById(R.id.gv);
    pb.setVisibility(View.GONE);
    initData();
    adapter = new SimpleAdapter(this, list, R.layout.item_layout,
        new String[] { "image", "text" }, new int[] { R.id.item_iv,
            R.id.item_tv });
    gv.setAdapter(adapter);
    gsDetector = new GestureDetector(this, new Mlistener());
    gv.setOnTouchListener(new OnTouchListener() {
      @Override
      public boolean onTouch(View v, MotionEvent event) {
        // Log.e("MainActivity", event.getX()+"");
        return gsDetector.onTouchEvent(event);
      }
    });
  }
  private void initData() {
    list = new ArrayList<Map<String, Object>>();
    for (int i = 0; i < 20; i++) {
      Map<String, Object> map = new HashMap<String, Object>();
      map.put("image", R.drawable.gift_item_default);
      map.put("text", "一只冰莹猪猪");
      list.add(map);
    }
  }
  class Mlistener implements OnGestureListener {
    @Override
    public boolean onDown(MotionEvent e) {
      return false;
    }
    @Override
    public void onShowPress(MotionEvent e) {
    }
    @Override
    public boolean onSingleTapUp(MotionEvent e) {
      return false;
    }
    @Override
    public boolean onScroll(MotionEvent e1, MotionEvent e2,
        float distanceX, float distanceY) {
      return false;
    }
    @Override
    public void onLongPress(MotionEvent e) {
    }
    @Override
    public boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX,
        float velocityY) {
      if (e2.getY() - e1.getY() > 0 && gv.getFirstVisiblePosition() == 0) {
        pb.setVisibility(View.VISIBLE);
        Animation animation = new ScaleAnimation(1f, 1f, 0, 1f);
        animation.setDuration(300);
        pb.startAnimation(animation);
        new Thread(new Runnable() {
          @Override
          public void run() {
            try {
              Thread.sleep(2000);
              Message msg = new Message();
              msg.what = 1;
              handler.sendMessage(msg);
            } catch (InterruptedException e) {
              // TODO Auto-generated catch block
              e.printStackTrace();
            }
          }
        }).start();
      }
      return false;
    }
  }
}

解析：
 在onCreate方法中先获取两个组件，然后把progressBar设置为隐藏，下拉的时候再显示，刷新完毕再隐藏。然后为GridView设置数据源，这里方便起见用SimpleAdapter，然后给GridView设置ontouchListener，并在onTouch方法中把触摸事件交给我们自定义的GestureDetector对象来处理，在GestureDetector的onFling方法中处理下拉事件，在里面判断是否下拉以及GridView是否在最顶端，如果是，显示progressBar控件并开一个线程来处理刷新，这里做模拟就睡眠2000毫秒，最后用message对象返回一个消息给Handler，Handler在主线程中更新GridView。

@Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    pb = (ProgressBar) findViewById(R.id.pb);
    gv = (GridView) findViewById(R.id.gv);
    pb.setVisibility(View.GONE);
    initData();
    adapter = new SimpleAdapter(this, list, R.layout.item_layout,
        new String[] { "image", "text" }, new int[] { R.id.item_iv,
            R.id.item_tv });
    gv.setAdapter(adapter);
    gsDetector = new GestureDetector(this, new Mlistener());
    gv.setOnTouchListener(new OnTouchListener() {
      @Override
      public boolean onTouch(View v, MotionEvent event) {
        // Log.e("MainActivity", event.getX()+"");
        return gsDetector.onTouchEvent(event);
      }
    });
  }

class Mlistener implements OnGestureListener {
    @Override
    public boolean onDown(MotionEvent e) {
      return false;
    }
    @Override
    public void onShowPress(MotionEvent e) {
    }
    @Override
    public boolean onSingleTapUp(MotionEvent e) {
      return false;
    }
    @Override
    public boolean onScroll(MotionEvent e1, MotionEvent e2,
        float distanceX, float distanceY) {
      return false;
    }
    @Override
    public void onLongPress(MotionEvent e) {
    }
    @Override
    public boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX,
        float velocityY) {
      if (e2.getY() - e1.getY() > 0 && gv.getFirstVisiblePosition() == 0) {
        pb.setVisibility(View.VISIBLE);
        Animation animation = new ScaleAnimation(1f, 1f, 0, 1f);
        animation.setDuration(300);
        pb.startAnimation(animation);
        new Thread(new Runnable() {
          @Override
          public void run() {
            try {
              Thread.sleep(2000);
              Message msg = new Message();
              msg.what = 1;
              handler.sendMessage(msg);
            } catch (InterruptedException e) {
              // TODO Auto-generated catch block
              e.printStackTrace();
            }
          }
        }).start();
      }
      return false;
    }
  }

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