Android开发学习之路-下拉刷新以及GridView的使用

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;
         }

     }