PullToRefresh 这个库用的是非常至多，github 今天主要分析一下源码实现.
我们通过ListView的下拉刷新进行分析，其它的类似。
整个下拉刷新 父View是LinearLayout， 在LinearLayout添加了Header View ,Footer View,和ListView
PullToRefreshBase 是父类 扩展了 LinearLayout水平布局 如果我们使用ListView 需要观看子类 PullToRefreshAdapterViewBase -> PullToRefreshListView
初始化代码在PullToRefreshBase init方法中
重点代码:
// Refreshable View
// By passing the attrs, we can add ListView/GridView params via XML
mRefreshableView = createRefreshableView(context, attrs);//通过子类传入的View,ListView或者ScrollView等
addRefreshableView(context, mRefreshableView);//添加view到布局中
// We need to create now layouts now 创建Header和Footer视图,默认是INVISIBLE，要添加到父窗口
mHeaderLayout = createLoadingLayout(context, Mode.PULL_FROM_START, a);
mFooterLayout = createLoadingLayout(context, Mode.PULL_FROM_END, a);
handleStyledAttributes(a);//添加loadingView效果，这里是把View添加到ListView HeaderView里面去
updateUIForMode(); //把布局添加到父View中 protected void updateUIForMode() {
final LinearLayout.LayoutParams lp = getLoadingLayoutLayoutParams();
// Remove Header, and then add Header Loading View again if needed
if (this == mHeaderLayout.getParent()) {
removeView(mHeaderLayout);
}
if (mMode.showHeaderLoadingLayout()) {
addViewInternal(mHeaderLayout, 0, lp);//加入View到LinearLayout
}
// Remove Footer, and then add Footer Loading View again if needed
if (this == mFooterLayout.getParent()) {
removeView(mFooterLayout);
}
if (mMode.showFooterLoadingLayout()) {
addViewInternal(mFooterLayout, lp);//加入View到LinearLayout
}
// Hide Loading Views
refreshLoadingViewsSize();//把headerView隐藏起来，其实用的是padding的方式 设置为负值 就到屏幕顶部的外面了
// If we're not using Mode.BOTH, set mCurrentMode to mMode, otherwise
// set it to pull down
mCurrentMode = (mMode != Mode.BOTH) ? mMode : Mode.PULL_FROM_START;
}//这里有2个LoadingView，一个是加入到LinearLayout中去了，还有一个是加入到ListView本身的Header里面
看看handleStyledAttributes方法 定位到子类复写的地方
FrameLayout frame = new FrameLayout(getContext());
mHeaderLoadingView = createLoadingLayout(getContext(), Mode.PULL_FROM_START, a);
mHeaderLoadingView.setVisibility(View.GONE);
frame.addView(mHeaderLoadingView, lp);
mRefreshableView.addHeaderView(frame, null, false);//添加LoadingView到ListView Header上
//headerView一共有2个LoadingView,一个是被加入到LinearLayout一个是被加入到ListView的HeaderView
addViewInternal方法就是加入到LinearLayout父类中
看看LoadingLayout 有2种 FlipLoadingLayout 和 RotateLoadingLayout 一般我们用旋转的加载动画
左边一个旋转图片，右边是文字和时间提示
第一个LoadingLayout主要显示 ：下拉刷新，放开以刷新
第二个LoadingLayout显示松手后的文字：正在载入…
结构是这样
当UI初始化好，下面看看onTouch 下拉捕获事件
public final boolean onTouchEvent(MotionEvent event) {
if (!isPullToRefreshEnabled()) {
return false;
}
// If we're refreshing, and the flag is set. Eat the event
if (!mScrollingWhileRefreshingEnabled && isRefreshing()) {
return true;
}
if (event.getAction() == MotionEvent.ACTION_DOWN && event.getEdgeFlags() != 0) {
return false;
}
switch (event.getAction()) {
case MotionEvent.ACTION_MOVE: {
if (mIsBeingDragged) {
mLastMotionY = event.getY();
mLastMotionX = event.getX();
pullEvent();//开始下拉，移动
return true;
}
break;
}
case MotionEvent.ACTION_DOWN: {
if (isReadyForPull()) {//按下 开始下拉
mLastMotionY = mInitialMotionY = event.getY();
mLastMotionX = mInitialMotionX = event.getX();
return true;
}
break;
}
case MotionEvent.ACTION_CANCEL:
case MotionEvent.ACTION_UP: { //停止下拉的时候
if (mIsBeingDragged) {
mIsBeingDragged = false;
if (mState == State.RELEASE_TO_REFRESH
&& (null != mOnRefreshListener || null != mOnRefreshListener2)) {
setState(State.REFRESHING, true);//放下手指开始回调，执行我们的回调任务
return true;
}
// If we're already refreshing, just scroll back to the top
if (isRefreshing()) {
smoothScrollTo(0);
return true;
}
// If we haven't returned by here, then we're not in a state
// to pull, so just reset
setState(State.RESET); //恢复到原来的UI状态
return true;
}
break;
}
}
return false;
}看看pullEvent方法
private void pullEvent() {
final int newScrollValue;
final int itemDimension;
final float initialMotionValue, lastMotionValue;
switch (getPullToRefreshScrollDirection()) {
case HORIZONTAL:
initialMotionValue = mInitialMotionX;
lastMotionValue = mLastMotionX;
break;
case VERTICAL:
default:
initialMotionValue = mInitialMotionY;
lastMotionValue = mLastMotionY;
break;
}
//计算下拉移动了多少
switch (mCurrentMode) {
case PULL_FROM_END://上拉
newScrollValue = Math.round(Math.max(initialMotionValue - lastMotionValue, 0) / FRICTION);
itemDimension = getFooterSize();
break;
case PULL_FROM_START://下拉
default:
newScrollValue = Math.round(Math.min(initialMotionValue - lastMotionValue, 0) / FRICTION);
itemDimension = getHeaderSize();
break;
}
//显示HeaderView 得到移动的值，可以让LoadingView显示出来
setHeaderScroll(newScrollValue);
if (newScrollValue != 0 && !isRefreshing()) {
float scale = Math.abs(newScrollValue) / (float) itemDimension;
switch (mCurrentMode) {
case PULL_FROM_END:
mFooterLayout.onPull(scale);
break;
case PULL_FROM_START:
default:
mHeaderLayout.onPull(scale);//旋转左边的加载图片，显示文字和图片 这个地方最终会执行LoadingLayout中的 onPullImpl方法
break;
}
//更新状态 包括2中 释放按下触摸，还有就是 没释放手的触摸
if (mState != State.PULL_TO_REFRESH && itemDimension >= Math.abs(newScrollValue)) {
setState(State.PULL_TO_REFRESH);
} else if (mState == State.PULL_TO_REFRESH && itemDimension < Math.abs(newScrollValue)) {
setState(State.RELEASE_TO_REFRESH);//下拉松手 可以松手了
}
}
}再看看setHeaderScroll方法代码
protected final void setHeaderScroll(int value) {
if (DEBUG) {
Log.d(LOG_TAG, "setHeaderScroll: " + value);
}
if (DEBUG) {
Log.d(LOG_TAG, "setHeaderScroll:" + value );
}
// Clamp value to with pull scroll range
final int maximumPullScroll = getMaximumPullScroll();
value = Math.min(maximumPullScroll, Math.max(-maximumPullScroll, value));
if (mLayoutVisibilityChangesEnabled) {
if (value < 0) { //有位移才显示
mHeaderLayout.setVisibility(View.VISIBLE);
} else if (value > 0) { <span style="font-family: Arial, Helvetica, sans-serif;">//有位移才显示</span>
mFooterLayout.setVisibility(View.VISIBLE);
} else {
mHeaderLayout.setVisibility(View.INVISIBLE);
mFooterLayout.setVisibility(View.INVISIBLE);
}
}
if (USE_HW_LAYERS) {
/**
* Use a Hardware Layer on the Refreshable View if we've scrolled at
* all. We don't use them on the Header/Footer Views as they change
* often, which would negate any HW layer performance boost.
*/
ViewCompat.setLayerType(mRefreshableViewWrapper, value != 0 ? View.LAYER_TYPE_HARDWARE
: View.LAYER_TYPE_NONE);
}
//回到最原始的scrollTo 最常用的 移动布局
switch (getPullToRefreshScrollDirection()) {
case VERTICAL:
scrollTo(0, value);
break;
case HORIZONTAL:
scrollTo(value, 0);
break;
}
}setState(State.REFRESHING, true);//拉倒最顶部 松手，会执行onRefreshing方法，回调我们实现的任务接口 也就是OnRefreshListener
protected void onRefreshing(final boolean doScroll) {
if (mMode.showHeaderLoadingLayout()) {
mHeaderLayout.refreshing();
}
if (mMode.showFooterLoadingLayout()) {
mFooterLayout.refreshing();
}
if (doScroll) {
if (mShowViewWhileRefreshing) {
// Call Refresh Listener when the Scroll has finished
OnSmoothScrollFinishedListener listener = new OnSmoothScrollFinishedListener() {
@Override
public void onSmoothScrollFinished() {
callRefreshListener();//回调接口执行
}
};
switch (mCurrentMode) {
case MANUAL_REFRESH_ONLY:
case PULL_FROM_END:
smoothScrollTo(getFooterSize(), listener);
break;
default:
case PULL_FROM_START:
smoothScrollTo(-getHeaderSize(), listener);
break;
}
} else {
smoothScrollTo(0);//回到原来的位置
}
} else {
// We're not scrolling, so just call Refresh Listener now
callRefreshListener();//回调接口执行
}
} private void callRefreshListener() {
if (null != mOnRefreshListener) {
mOnRefreshListener.onRefresh(this);//回调
} else if (null != mOnRefreshListener2) { //这个是上拉，下拉都可以的情况，使用 onRefreshListener2
if (mCurrentMode == Mode.PULL_FROM_START) {
mOnRefreshListener2.onPullDownToRefresh(this);
} else if (mCurrentMode == Mode.PULL_FROM_END) {
mOnRefreshListener2.onPullUpToRefresh(this);
}
}
}总结：状态包括下拉刷新，松手刷新，正在刷新，Loading隐藏。移动UI还是用的scrollTo最基本的代码. 动画部分可以看LoadingLayout的2个子类
主要的就这些，还有很多细节没有分析。若有问题请指出谢谢。
