PullToRefresh 这个库用的是很至多。github 今天主要分析一下源代码实现.
我们通过ListView的下拉刷新进行分析。其他的类似。
整个下拉刷新 父View是LinearLayout， 在LinearLayout加入了Header View ,Footer View,和ListView
PullToRefreshBase 是父类 扩展了 LinearLayout水平布局 假设我们使用ListView 须要观看子类 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);//加入view到布局中 // We need to create now layouts now 创建Header和Footer视图,默认是INVISIBLE。要加入到父窗体
mHeaderLayout = createLoadingLayout(context, Mode.PULL_FROM_START, a);
mFooterLayout = createLoadingLayout(context, Mode.PULL_FROM_END, a); handleStyledAttributes(a);//加入loadingView效果。这里是把View加入到ListView HeaderView里面去
updateUIForMode(); //把布局加入到父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);//增加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);//增加View到LinearLayout
}
// Hide Loading Views
refreshLoadingViewsSize();//把headerView隐藏起来，其有用的是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，一个是增加到LinearLayout中去了，另一个是增加到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);//加入LoadingView到ListView Header上
//headerView一共同拥有2个LoadingView,一个是被增加到LinearLayout一个是被增加到ListView的HeaderView
addViewInternal方法就是增加到LinearLayout父类中
看看LoadingLayout 有2种 FlipLoadingLayout 和 RotateLoadingLayout 一般我们用旋转的载入动画
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：正在加载...
结构是这样
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当UI初始化好，以下看看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();//開始下拉，移动
return true;
}
break;
}
case MotionEvent.ACTION_DOWN: {
if (isReadyForPull()) {//按下 開始下拉
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);//放下手指開始回调，运行我们的回调任务
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。能够让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);//旋转左边的载入图片，显示文字和图片 这个地方终于会运行LoadingLayout中的 onPullImpl方法
break;
}
//更新状态 包含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 能够松手了
}
}
}
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 最经常使用的 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，会运行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();//回调接口运行
}
};
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();//回调接口运行
}
}
private void callRefreshListener() {
if (null != mOnRefreshListener) {
mOnRefreshListener.onRefresh(this);//回调
} else if (null != mOnRefreshListener2) { //这个是上拉，下拉都能够的情况，使用 onRefreshListener2
if (mCurrentMode == Mode.PULL_FROM_START) {
mOnRefreshListener2.onPullDownToRefresh(this);
} else if (mCurrentMode == Mode.PULL_FROM_END) {
mOnRefreshListener2.onPullUpToRefresh(this);
}
}
}
总结：状态包含下拉刷新。松手刷新，正在刷新，Loading隐藏。移动UI还是用的scrollTo最主要的代码. 动画部分能够看LoadingLayout的2个子类
基本的就这些。还有非常多细节没有分析。若有问题请指出谢谢。