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;
        }

    }