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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