带有下拉刷新功能的Listview控件

效果图如下

1.原理

其实就是继承了Listview控件，为其默认加一个header，这个header就是带箭头的那些东西。然后overrideonTouchEvent函数，根据滑动过程中y坐标的变化来动态修改header的状态（包括箭头的方向和文字提示），其他用法和普通的Listview一样。

public class PullToRefreshListView extends ListView implements OnScrollListener 
{

	private static final String TAG = "PullToRefreshListView";

	private final static int RELEASE_TO_REFRESH = 0;
	private final static int PULL_TO_REFRESH = 1;
	private final static int REFRESHING = 2;
	private final static int DONE = 3;
	private final static int LOADING = 4;

	// 实际的padding的距离与界面上偏移距离的比例
	private final static int RATIO = 3;
	private LayoutInflater inflater;

	//listview的头部 用于显示刷新的箭头等
	private LinearLayout headView;
	private TextView tipsTextview;
	private TextView lastUpdatedTextView;
	private ImageView arrowImageView;
	private ProgressBar progressBar;

	//箭头旋转的动画
	private RotateAnimation animation;
	private RotateAnimation reverseAnimation;

	// 用于保证startY的值在一个完整的touch事件中只被记录一次
	private boolean isRecored;
	private int headContentWidth;
	private int headContentHeight;
	private int startY;
	private int firstItemIndex;
	private int state;
	private boolean isBack;

	private OnRefreshListener refreshListener;

	private boolean isRefreshable;

	public PullToRefreshListView(Context context) 
	{
		super(context);
		init(context);
	}

	public PullToRefreshListView(Context context, AttributeSet attrs) 
	{
		super(context, attrs);
		init(context);
	}

	private void init(Context context)
	{
		setCacheColorHint(context.getResources().getColor(R.color.transparent));
		inflater = LayoutInflater.from(context);
		headView = (LinearLayout) inflater.inflate(R.layout.head, null);

		arrowImageView = (ImageView) headView
				.findViewById(R.id.head_arrowImageView);
		arrowImageView.setMinimumWidth(70);
		arrowImageView.setMinimumHeight(50);
		progressBar = (ProgressBar) headView
				.findViewById(R.id.head_progressBar);
		tipsTextview = (TextView) headView.findViewById(R.id.head_tipsTextView);
		lastUpdatedTextView = (TextView) headView
				.findViewById(R.id.head_lastUpdatedTextView);

		measureView(headView);
		headContentHeight = headView.getMeasuredHeight();
		headContentWidth = headView.getMeasuredWidth();

		headView.setPadding(0, -1 * headContentHeight, 0, 0);
		headView.invalidate();

		Log.v("size", "width:" + headContentWidth + " height:"
				+ headContentHeight);

		addHeaderView(headView, null, false);
		setOnScrollListener(this);

		animation = new RotateAnimation(0, -180,
				RotateAnimation.RELATIVE_TO_SELF, 0.5f,
				RotateAnimation.RELATIVE_TO_SELF, 0.5f);
		animation.setInterpolator(new LinearInterpolator());
		animation.setDuration(250);
		animation.setFillAfter(true);

		reverseAnimation = new RotateAnimation(-180, 0,
				RotateAnimation.RELATIVE_TO_SELF, 0.5f,
				RotateAnimation.RELATIVE_TO_SELF, 0.5f);
		reverseAnimation.setInterpolator(new LinearInterpolator());
		reverseAnimation.setDuration(200);
		reverseAnimation.setFillAfter(true);

		state = DONE;
		isRefreshable = false;
	}

	@Override
	public void onScroll(AbsListView arg0, int firstVisiableItem, int arg2, int arg3) 
	{
		firstItemIndex = firstVisiableItem;
	}

	@Override
	public void onScrollStateChanged(AbsListView arg0, int arg1)
	{
	}

	@Override
	public boolean onTouchEvent(MotionEvent event) 
	{
		if (isRefreshable) 
		{
			switch (event.getAction()) 
			{
			case MotionEvent.ACTION_DOWN:
				if (firstItemIndex == 0 && !isRecored) 
				{
					isRecored = true;
					startY = (int) event.getY();
					Log.v(TAG, "在down时候记录当前位置");
				}
				break;
			case MotionEvent.ACTION_UP:
				if (state != REFRESHING && state != LOADING) {
					if (state == DONE) {
						// 什么都不做
					}
					if (state == PULL_TO_REFRESH) {
						state = DONE;
						changeHeaderViewByState();

						Log.v(TAG, "由下拉刷新状态，到done状态");
					}
					if (state == RELEASE_TO_REFRESH) {
						state = REFRESHING;
						changeHeaderViewByState();
						onRefresh();

						Log.v(TAG, "由松开刷新状态，到done状态");
					}
				}
				isRecored = false;
				isBack = false;
				break;
			case MotionEvent.ACTION_MOVE:
				int tempY = (int) event.getY();
				if (!isRecored && firstItemIndex == 0) {
					Log.v(TAG, "在move时候记录下位置");
					isRecored = true;
					startY = tempY;
				}
				if (state != REFRESHING && isRecored && state != LOADING) {
					// 保证在设置padding的过程中，当前的位置一直是在head，否则如果当列表超出屏幕的话，当在上推的时候，列表会同时进行滚动
					// 可以松手去刷新了
					if (state == RELEASE_TO_REFRESH) {
						setSelection(0);
						// 往上推了，推到了屏幕足够掩盖head的程度，但是还没有推到全部掩盖的地步
						if (((tempY - startY) / RATIO < headContentHeight)
								&& (tempY - startY) > 0) {
							state = PULL_TO_REFRESH;
							changeHeaderViewByState();
							Log.v(TAG, "由松开刷新状态转变到下拉刷新状态");
						}
						// 一下子推到顶了
						else if (tempY - startY <= 0) {
							state = DONE;
							changeHeaderViewByState();
							Log.v(TAG, "由松开刷新状态转变到done状态");
						}
						// 往下拉了，或者还没有上推到屏幕顶部掩盖head的地步
						else {
							// 不用进行特别的操作，只用更新paddingTop的值就行了
						}
					}
					// 还没有到达显示松开刷新的时候,DONE或者是PULL_To_REFRESH状态
					if (state == PULL_TO_REFRESH) {
						setSelection(0);
						// 下拉到可以进入RELEASE_TO_REFRESH的状态
						if ((tempY - startY) / RATIO >= headContentHeight) {
							state = RELEASE_TO_REFRESH;
							isBack = true;
							changeHeaderViewByState();
							Log.v(TAG, "由done或者下拉刷新状态转变到松开刷新");
						}
						// 上推到顶了
						else if (tempY - startY <= 0) {
							state = DONE;
							changeHeaderViewByState();
							Log.v(TAG, "由DOne或者下拉刷新状态转变到done状态");
						}
					}
					// done状态下
					if (state == DONE) {
						if (tempY - startY > 0) {
							state = PULL_TO_REFRESH;
							changeHeaderViewByState();
						}
					}
					// 更新headView的size
					if (state == PULL_TO_REFRESH) {
						headView.setPadding(0, -1 * headContentHeight + (tempY - startY) / RATIO, 0, 0);
					}
					// 更新headView的paddingTop
					if (state == RELEASE_TO_REFRESH) {
						headView.setPadding(0, (tempY - startY) / RATIO
								- headContentHeight, 0, 0);
					}
				}
				break;
			}
		}

		return super.onTouchEvent(event);
	}

	// 当状态改变时候，调用该方法，以更新界面
	private void changeHeaderViewByState()
	{
		switch (state) 
		{
		case RELEASE_TO_REFRESH:
			arrowImageView.setVisibility(View.VISIBLE);
			progressBar.setVisibility(View.GONE);
			tipsTextview.setVisibility(View.VISIBLE);
			lastUpdatedTextView.setVisibility(View.VISIBLE);

			arrowImageView.clearAnimation();
			arrowImageView.startAnimation(animation);
			tipsTextview.setText("放开以刷新");
			Log.v(TAG, "当前状态，松开刷新");
			break;
		case PULL_TO_REFRESH:
			progressBar.setVisibility(View.GONE);
			tipsTextview.setVisibility(View.VISIBLE);
			lastUpdatedTextView.setVisibility(View.VISIBLE);
			arrowImageView.clearAnimation();
			arrowImageView.setVisibility(View.VISIBLE);
			// 是由RELEASE_To_REFRESH状态转变来的
			if (isBack) {
				isBack = false;
				arrowImageView.clearAnimation();
				arrowImageView.startAnimation(reverseAnimation);
				tipsTextview.setText("下拉刷新");
			} else {
				tipsTextview.setText("下拉刷新");
			}
			Log.v(TAG, "当前状态，下拉刷新");
			break;

		case REFRESHING:
			headView.setPadding(0, 0, 0, 0);
			progressBar.setVisibility(View.VISIBLE);
			arrowImageView.clearAnimation();
			arrowImageView.setVisibility(View.GONE);
			tipsTextview.setText("正在刷新...");
			lastUpdatedTextView.setVisibility(View.VISIBLE);
			Log.v(TAG, "当前状态,正在刷新...");
			break;
		case DONE:
			headView.setPadding(0, -1 * headContentHeight, 0, 0);
			progressBar.setVisibility(View.GONE);
			arrowImageView.clearAnimation();
			arrowImageView.setImageResource(R.drawable.arrow);
			tipsTextview.setText("下拉刷新");
			lastUpdatedTextView.setVisibility(View.VISIBLE);
			Log.v(TAG, "当前状态，done");
			break;
		}
	}

	public void setonRefreshListener(OnRefreshListener refreshListener)
	{
		this.refreshListener = refreshListener;
		isRefreshable = true;
	}

	public interface OnRefreshListener 
	{
		public void onRefresh();
	}

	public void onRefreshComplete()
	{
		state = DONE;
		lastUpdatedTextView.setText("最近更新:" + new Date().toLocaleString());
		changeHeaderViewByState();
	}

	private void onRefresh() 
	{
		if (refreshListener != null)
		{
			refreshListener.onRefresh();
		}
	}

	// 此方法直接照搬自网络上的一个下拉刷新的demo，此处是“估计”headView的width以及height
	private void measureView(View child) {
		ViewGroup.LayoutParams p = child.getLayoutParams();
		if (p == null) {
			p = new ViewGroup.LayoutParams(ViewGroup.LayoutParams.FILL_PARENT,
					ViewGroup.LayoutParams.WRAP_CONTENT);
		}
		int childWidthSpec = ViewGroup.getChildMeasureSpec(0, 0 + 0, p.width);
		int lpHeight = p.height;
		int childHeightSpec;
		if (lpHeight > 0) {
			childHeightSpec = MeasureSpec.makeMeasureSpec(lpHeight,
					MeasureSpec.EXACTLY);
		} else {
			childHeightSpec = MeasureSpec.makeMeasureSpec(0,
					MeasureSpec.UNSPECIFIED);
		}
		child.measure(childWidthSpec, childHeightSpec);
	}

	public void setAdapter(BaseAdapter adapter)
	{
		lastUpdatedTextView.setText("最近更新:" + new Date().toLocaleString());
		super.setAdapter(adapter);
	}

}

header的layout xml

2.如何使用

使用起来很简单，只有一点不同，要实现OnRefreshListener接口，标志当下拉刷新的时候你所要做的事情。

listView.setonRefreshListener(new OnRefreshListener() {
	@Override
	public void onRefresh() 
	{
		new AsyncTask() {
                        //刷新过程中需要做的操作在这里
			protected Void doInBackground(Void... params)
			{
				try 
				{
					Thread.sleep(1000);
				} 
				catch (Exception e) 
				{
					e.printStackTrace();
				}
				data.add("new item");
				return null;
			}
                        //刷新完成后要通知listview进行界面调整
			@Override
			protected void onPostExecute(Void result) 
			{
				adapter.notifyDataSetChanged();
				listView.onRefreshComplete();
			}

		}.execute(null);
	}
});