带有下拉刷新功能的Listview控件

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override onTouchEvent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。

[java] view plaincopy

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

[html] view plaincopy

<?xml version="1.0" encoding="utf-8"?>
<!-- ListView的头部 -->
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
>
<!-- 内容 -->
<RelativeLayout
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:id="@+id/head_contentLayout"
android:paddingLeft="30dp"
>
<!-- 箭头图像、进度条 -->
<FrameLayout
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentLeft="true"
android:layout_centerVertical="true"
>
<!-- 箭头 -->
<ImageView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:src="@drawable/arrow"
android:id="@+id/head_arrowImageView"
/>
<!-- 进度条 -->
<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。

[java] view plaincopy

listView.setonRefreshListener(new OnRefreshListener() {
@Override
public void onRefresh()
{
new AsyncTask<Void, Void, Void>() {
//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);
}
});