帶有下拉刷新功能的Listview控件

效果圖以下

1.原理

其實就是繼承了Listview控件，爲其默認加一個header，這個header就是帶箭頭的那些東西。而後override onTouchEvent函數，根據滑動過程當中y座標的變化來動態修改header的狀態（包括箭頭的方向和文字提示），其餘用法和普通的Listview同樣。

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;

	// 實際的padding的距離與界面上偏移距離的比例
	private final static int RATIO = 3;
	private LayoutInflater inflater;

	//listview的頭部 用於顯示刷新的箭頭等
	private LinearLayout headView;
	private TextView tipsTextview;
	private TextView lastUpdatedTextView;
	private ImageView arrowImageView;
	private ProgressBar progressBar;

	//箭頭旋轉的動畫
	private RotateAnimation animation;
	private RotateAnimation reverseAnimation;

	// 用於保證startY的值在一個完整的touch事件中只被記錄一次
	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時候記錄當前位置");
				}
				break;
			case MotionEvent.ACTION_UP:
				if (state != REFRESHING && state != LOADING) {
					if (state == DONE) {
						// 什麼都不作
					}
					if (state == PULL_TO_REFRESH) {
						state = DONE;
						changeHeaderViewByState();

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

						Log.v(TAG, "由鬆開刷新狀態，到done狀態");
					}
				}
				isRecored = false;
				isBack = false;
				break;
			case MotionEvent.ACTION_MOVE:
				int tempY = (int) event.getY();
				if (!isRecored && firstItemIndex == 0) {
					Log.v(TAG, "在move時候記錄下位置");
					isRecored = true;
					startY = tempY;
				}
				if (state != REFRESHING && isRecored && state != LOADING) {
					// 保證在設置padding的過程當中，當前的位置一直是在head，不然若是當列表超出屏幕的話，當在上推的時候，列表會同時進行滾動
					// 能夠鬆手去刷新了
					if (state == RELEASE_TO_REFRESH) {
						setSelection(0);
						// 往上推了，推到了屏幕足夠掩蓋head的程度，可是尚未推到所有掩蓋的地步
						if (((tempY - startY) / RATIO < headContentHeight)
								&& (tempY - startY) > 0) {
							state = PULL_TO_REFRESH;
							changeHeaderViewByState();
							Log.v(TAG, "由鬆開刷新狀態轉變到下拉刷新狀態");
						}
						// 一會兒推到頂了
						else if (tempY - startY <= 0) {
							state = DONE;
							changeHeaderViewByState();
							Log.v(TAG, "由鬆開刷新狀態轉變到done狀態");
						}
						// 往下拉了，或者尚未上推到屏幕頂部掩蓋head的地步
						else {
							// 不用進行特別的操做，只用更新paddingTop的值就好了
						}
					}
					// 尚未到達顯示鬆開刷新的時候,DONE或者是PULL_To_REFRESH狀態
					if (state == PULL_TO_REFRESH) {
						setSelection(0);
						// 下拉到能夠進入RELEASE_TO_REFRESH的狀態
						if ((tempY - startY) / RATIO >= headContentHeight) {
							state = RELEASE_TO_REFRESH;
							isBack = true;
							changeHeaderViewByState();
							Log.v(TAG, "由done或者下拉刷新狀態轉變到鬆開刷新");
						}
						// 上推到頂了
						else if (tempY - startY <= 0) {
							state = DONE;
							changeHeaderViewByState();
							Log.v(TAG, "由DOne或者下拉刷新狀態轉變到done狀態");
						}
					}
					// done狀態下
					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);
	}

	// 當狀態改變時候，調用該方法，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("放開以刷新");
			Log.v(TAG, "當前狀態，鬆開刷新");
			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狀態轉變來的
			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, "當前狀態，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, "當前狀態,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, "當前狀態，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();
		}
	}

	// 此方法直接照搬自網絡上的一個下拉刷新的demo，此處是「估計」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

<?xml version="1.0" encoding="utf-8"?>
<!-- ListView的頭部 -->
<LinearLayout
  xmlns:android="http://schemas.android.com/apk/res/android"
  android:layout_width="fill_parent"
  android:layout_height="wrap_content"
 >
  <!-- 內容 -->
  <RelativeLayout
  android:layout_width="fill_parent"
  android:layout_height="wrap_content"
  android:id="@+id/head_contentLayout"
  android:paddingLeft="30dp"
  >
  <!-- 箭頭圖像、進度條 -->
  <FrameLayout
  android:layout_width="wrap_content"
  android:layout_height="wrap_content"
  android:layout_alignParentLeft="true"
  android:layout_centerVertical="true"
  >
  <!-- 箭頭 -->
  <ImageView
  android:layout_width="wrap_content"
  android:layout_height="wrap_content"
  android:layout_gravity="center"
  android:src="@drawable/arrow"
  android:id="@+id/head_arrowImageView"
  />
  <!-- 進度條 -->
  <ProgressBar
  android:layout_width="wrap_content"
  android:layout_height="wrap_content"
  style="?android:attr/progressBarStyleSmall"
  android:layout_gravity="center"
  android:id="@+id/head_progressBar"
  android:visibility="gone"
  />
  
  </FrameLayout>
  <!-- 提示、最近更新 -->
  <LinearLayout
  android:layout_width="wrap_content"
  android:layout_height="wrap_content"
  android:layout_centerHorizontal="true"
  android:orientation="vertical"
  android:gravity="center_horizontal"
  >
  <!-- 提示 -->
  <TextView
  android:layout_width="wrap_content"
  android:layout_height="wrap_content"
  android:text="下拉刷新"
  android:textColor="#33CCFF"
  android:textSize="20sp"
  android:id="@+id/head_tipsTextView"
  />
  <!-- 最近更新 --> 
  <TextView
  android:layout_width="wrap_content"
  android:layout_height="wrap_content"
  android:id="@+id/head_lastUpdatedTextView"
  android:text="上次更新"
  android:textColor="@color/gold"
  android:textSize="10sp"
  />
  </LinearLayout>
  </RelativeLayout>
</LinearLayout>

2.如何使用

使用起來很簡單，只有一點不一樣，要實現OnRefreshListener接口，標誌當下拉刷新的時候你所要作的事情。

listView.setonRefreshListener(new OnRefreshListener() {
	@Override
	public void onRefresh() 
	{
		new AsyncTask<Void, Void, Void>() {
                        //刷新過程當中須要作的操做在這裏
			protected Void doInBackground(Void... params)
			{
				try 
				{
					Thread.sleep(1000);
				} 
				catch (Exception e) 
				{
					e.printStackTrace();
				}
				data.add("new item");
				return null;
			}
                        //刷新完成後要通知listview進行界面調整
			@Override
			protected void onPostExecute(Void result) 
			{
				adapter.notifyDataSetChanged();
				listView.onRefreshComplete();
			}

		}.execute(null);
	}
});