指令汇B新闻客户端开发（三） 下拉刷新

现在我们继续这个新闻客户端的开发，今天分享的是下拉刷新的实现，我们都知道下拉刷新是一个应用很常见也很实用的功能。我这个应用是通过拉ListView来实现刷新的，先看一张刷新的原理图

从图中可知，手指移动的距离就是dy。

刷新分为三种状态：下拉刷新、正在刷新、松开刷新；

定义这三种状态为：

private static final int STATE_PULL_REFRESH = 0;// 下拉刷新
private static final int STATE_RELEASE_REFRESH = 1;// 松开刷新
private static final int STATE_REFRESHING = 2;// 正在刷新

接下来开始写我们的代码了

初始化头布局：

private void initHeaderView() {
		mHeaderView = View.inflate(getContext(), R.layout.refresh_header, null);
		this.addHeaderView(mHeaderView);

		tvTitle = (TextView) mHeaderView.findViewById(R.id.tv_title);
		tvTime = (TextView) mHeaderView.findViewById(R.id.tv_time);
		ivArrow = (ImageView) mHeaderView.findViewById(R.id.iv_arr);
		pbProgress = (ProgressBar) mHeaderView.findViewById(R.id.pb_progress);

		mHeaderView.measure(0, 0);
		mHeaderViewHeight = mHeaderView.getMeasuredHeight();

		mHeaderView.setPadding(0, -mHeaderViewHeight, 0, 0);// 隐藏头布局

		initArrowAnim();

		tvTime.setText("最后刷新时间:" + getCurrentTime());
	}

 * 初始化脚布局
	 */
	private void initFooterView() {
		mFooterView = View.inflate(getContext(),
				R.layout.refresh_listview_footer, null);
		this.addFooterView(mFooterView);

		mFooterView.measure(0, 0);
		mFooterViewHeight = mFooterView.getMeasuredHeight();

		mFooterView.setPadding(0, -mFooterViewHeight, 0, 0);// 隐藏

		this.setOnScrollListener(this);
	}

/**
	 * 初始化箭头动画
	 */
	private void initArrowAnim() {
		// 箭头向上动画
		animUp = new RotateAnimation(0, -180, Animation.RELATIVE_TO_SELF, 0.5f,
				Animation.RELATIVE_TO_SELF, 0.5f);
		animUp.setDuration(200); 
		animUp.setFillAfter(true);

		// 箭头向下动画
		animDown = new RotateAnimation(-180, 0, Animation.RELATIVE_TO_SELF,
				0.5f, Animation.RELATIVE_TO_SELF, 0.5f);
		animDown.setDuration(200);
		animDown.setFillAfter(true);

	}

接下来是实现触摸的方法及偏移量的计算：

@Override
	public boolean onTouchEvent(MotionEvent ev) {
		switch (ev.getAction()) {
		case MotionEvent.ACTION_DOWN:
			startY = (int) ev.getRawY();
			break;
		case MotionEvent.ACTION_MOVE:
			if (startY == -1) {// 确保startY有效
				startY = (int) ev.getRawY();
			}

			if (mCurrrentState == STATE_REFRESHING) {// 正在刷新时不做处理
				break;
			}

			int endY = (int) ev.getRawY();
			int dy = endY - startY;// 移动偏移量

			if (dy > 0 && getFirstVisiblePosition() == 0) {// 只有下拉并且当前是第一个item,才允许下拉
				int padding = dy - mHeaderViewHeight;// 计算padding
				mHeaderView.setPadding(0, padding, 0, 0);// 设置当前padding

				if (padding > 0 && mCurrrentState != STATE_RELEASE_REFRESH) {// 状态改为松开刷新
					mCurrrentState = STATE_RELEASE_REFRESH;
					refreshState();
				} else if (padding < 0 && mCurrrentState != STATE_PULL_REFRESH) {// 改为下拉刷新状态
					mCurrrentState = STATE_PULL_REFRESH;
					refreshState();
				}

				return true;
			}

			break;
		case MotionEvent.ACTION_UP:
			startY = -1;// 重置

			if (mCurrrentState == STATE_RELEASE_REFRESH) {
				mCurrrentState = STATE_REFRESHING;// 正在刷新
				mHeaderView.setPadding(0, 0, 0, 0);// 显示
				refreshState();
			} else if (mCurrrentState == STATE_PULL_REFRESH) {
				mHeaderView.setPadding(0, -mHeaderViewHeight, 0, 0);// 隐藏
			}

			break;

		default:
			break;
		}
		return super.onTouchEvent(ev);
	}

private void refreshState() {
		switch (mCurrrentState) {
		case STATE_PULL_REFRESH:
			tvTitle.setText("下拉刷新");
			ivArrow.setVisibility(View.VISIBLE);
			pbProgress.setVisibility(View.INVISIBLE);
			ivArrow.startAnimation(animDown);
			break;
		case STATE_RELEASE_REFRESH:
			tvTitle.setText("松开刷新");
			ivArrow.setVisibility(View.VISIBLE);
			pbProgress.setVisibility(View.INVISIBLE);
			ivArrow.startAnimation(animUp);
			break;
		case STATE_REFRESHING:
			tvTitle.setText("正在刷新...");
			ivArrow.clearAnimation();// 必须先清除动画,才能隐藏
			ivArrow.setVisibility(View.INVISIBLE);
			pbProgress.setVisibility(View.VISIBLE);

			if (mListener != null) {
				mListener.onRefresh();
			}
			break;

		default:
			break;
		}
	}

/*
	 * 收起下拉刷新的控件
	 */
	public void onRefreshComplete(boolean success) {
		if (isLoadingMore) {// 正在加载更多...
			mFooterView.setPadding(0, -mFooterViewHeight, 0, 0);// 隐藏脚布局
			isLoadingMore = false;
		} else {
			mCurrrentState = STATE_PULL_REFRESH;
			tvTitle.setText("下拉刷新");
			ivArrow.setVisibility(View.VISIBLE);
			pbProgress.setVisibility(View.INVISIBLE);

			mHeaderView.setPadding(0, -mHeaderViewHeight, 0, 0);// 隐藏

			if (success) {
				tvTime.setText("最后刷新时间:" + getCurrentTime());
			}
		}
	}

/**
	 * 获取当前时间
	 */
	public String getCurrentTime() {
		SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
		return format.format(new Date());
	}

	private boolean isLoadingMore;

	@Override
	public void onScrollStateChanged(AbsListView view, int scrollState) {
		if (scrollState == SCROLL_STATE_IDLE
				|| scrollState == SCROLL_STATE_FLING) {

			if (getLastVisiblePosition() == getCount() - 1 && !isLoadingMore) {// 滑动到最后
			//	System.out.println("到底了.....");
				mFooterView.setPadding(0, 0, 0, 0);// 显示
				setSelection(getCount() - 1);// 改变listview显示位置

				isLoadingMore = true;

				if (mListener != null) {
					mListener.onLoadMore();
				}
			}
		}
	}

// 设置下拉刷新监听
		lvList.setOnRefreshListener(new OnRefreshListener() {

			@Override
			public void onRefresh() {
				getDataFromServer();
			}

			@Override
			public void onLoadMore() {
				if (mMoreUrl != null) {
					getMoreDataFromServer();
				} else {
					Toast.makeText(mActivity, "最后一页了", Toast.LENGTH_SHORT)
							.show();
					lvList.onRefreshComplete(false);// 收起加载更多的布局
				}
			}
		});