下拉重新整理、上拉載入更多控制元件實現原理及解析(一)
以前那個賬號,以後可能不用了,把文章搬過來!!!
效果預覽
接受hi大頭鬼hi的建議,來一個動態圖,方便大家知道這是個什麼東西。
動機
原理
無論是下拉重新整理還是上拉載入更多,原理都是在內容View(ListView、RecyclerView…)不能下拉或者上劃時響應使用者的觸控事件,在頂部或者底部顯示一個重新整理檢視,在程式重新整理操作完成後再隱藏掉。
實現
既然要在頭部和頂部新增重新整理檢視,我們的控制元件應該是個ViewGroup,我是直接繼承FrameLayout,這個控制元件的名字叫NsRefreshLayout。然後我們需要定義一些屬性,如是否自動觸發上拉載入更多、重新整理檢視中的文字顏色等。
屬性定義
<declare-styleable name="NsRefreshLayout">
<!--Loading檢視背景顏色-->
<attr name="load_view_bg_color" format="color|reference"/>
<!--進度條顏色-->
<attr name="progress_bar_color" format="color|reference"/>
<!--進度條背景色-->
<attr name="progress_bg_color" format="color|reference"/>
<!--Loading檢視中文字顏色-->
<attr name="load_text_color" format="color|reference"/>
<!--下拉重新整理問題描述-->
<attr name="pull_refresh_text" format="string|reference"/>
<!--上拉載入文字描述-->
<attr name="pull_load_text" format="string|reference" />
<!--是否自動觸發載入更多-->
<attr name="auto_load_more" format="boolean"/>
<!--下拉重新整理是否可用-->
<attr name="pull_refresh_enable" format="boolean"/>
<!--上拉載入是否可用-->
<attr name="pull_load_enable" format="boolean"/>
</declare-styleable>
屬性讀取
/**
* 初始化控制元件屬性
*/
private void initAttrs(Context context, AttributeSet attrs) {
if (getChildCount() > 1) {
throw new RuntimeException("can only have one child");
}
loadingViewFinalHeight = NrlUtils.dipToPx(context, LOADING_VIEW_FINAL_HEIGHT_DP);
loadingViewOverHeight = loadingViewFinalHeight * 2;
if (isInEditMode() && attrs == null) {
return;
}
int resId;
TypedArray ta = context.obtainStyledAttributes(attrs, R.styleable.NsRefreshLayout);
Resources resources = context.getResources();
//LoadView背景顏色
resId = ta.getResourceId(R.styleable.NsRefreshLayout_load_view_bg_color, -1);
if (resId == -1) {
mLoadViewBgColor = ta.getColor(R.styleable.NsRefreshLayout_load_view_bg_color,
Color.WHITE);
} else {
mLoadViewBgColor = resources.getColor(resId);
}
//載入文字顏色
resId = ta.getResourceId(R.styleable.NsRefreshLayout_load_text_color, -1);
if (resId == -1) {
mLoadViewTextColor = ta.getColor(R.styleable.NsRefreshLayout_load_text_color,
Color.BLACK);
} else {
mLoadViewTextColor = resources.getColor(resId);
}
//進度條背景顏色
resId = ta.getResourceId(R.styleable.NsRefreshLayout_progress_bg_color, -1);
if (resId == -1) {
mProgressBgColor = ta.getColor(R.styleable.NsRefreshLayout_progress_bg_color,
Color.WHITE);
} else {
mProgressBgColor = resources.getColor(resId);
}
//進度條顏色
resId = ta.getResourceId(R.styleable.NsRefreshLayout_progress_bar_color, -1);
if (resId == -1) {
mProgressColor = ta.getColor(R.styleable.NsRefreshLayout_progress_bar_color,
Color.RED);
} else {
mProgressColor = resources.getColor(resId);
}
//下拉重新整理文字描述
resId = ta.getResourceId(R.styleable.NsRefreshLayout_pull_refresh_text, -1);
if (resId == -1) {
mPullRefreshText = ta.getString(R.styleable.NsRefreshLayout_pull_refresh_text);
} else {
mPullRefreshText = resources.getString(resId);
}
//上拉載入文字描述
resId = ta.getResourceId(R.styleable.NsRefreshLayout_pull_load_text, -1);
if (resId == -1) {
mPullLoadText = ta.getString(R.styleable.NsRefreshLayout_pull_load_text);
} else {
mPullLoadText = resources.getString(resId);
}
mAutoLoadMore = ta.getBoolean(R.styleable.NsRefreshLayout_auto_load_more, false);
mPullRefreshEnable = ta.getBoolean(R.styleable.NsRefreshLayout_pull_refresh_enable, true);
mPullLoadEnable = ta.getBoolean(R.styleable.NsRefreshLayout_pull_load_enable, true);
ta.recycle();
}
屬性使用
在內容View佈局完成後(onFinishInflate),根據設定的屬性,來確定是否需要新增下拉重新整理檢視、上拉載入更多檢視,以及檢視中的文字顏色、進度條顏色等。
@Override
protected void onFinishInflate() {
super.onFinishInflate();
mContentView = getChildAt(0);
setupViews();
}
private void setupViews() {
//下拉重新整理檢視
LayoutParams lp;
if (mPullRefreshEnable) {
lp = new LayoutParams(LayoutParams.MATCH_PARENT, 0);
headerView = new LoadView(getContext());
headerView.setLoadText(TextUtils.isEmpty(mPullRefreshText) ?
getContext().getString(R.string.default_pull_refresh_text) : mPullRefreshText);
headerView.setStartEndTrim(0, 0.75f);
headerView.setBackgroundColor(mLoadViewBgColor);
headerView.setLoadTextColor(mLoadViewTextColor);
headerView.setProgressBgColor(mProgressBgColor);
headerView.setProgressColor(mProgressColor);
addView(headerView, lp);
}
if (mPullLoadEnable) {
//上拉載入更多檢視
lp = new LayoutParams(LayoutParams.MATCH_PARENT, 0);
lp.gravity = Gravity.BOTTOM;
footerView = new LoadView(getContext());
footerView.setLoadText(TextUtils.isEmpty(mPullLoadText) ?
getContext().getString(R.string.default_pull_load_text) : mPullLoadText);
footerView.setStartEndTrim(0.5f, 1.25f);
footerView.setBackgroundColor(mLoadViewBgColor);
footerView.setLoadTextColor(mLoadViewTextColor);
footerView.setProgressBgColor(mProgressBgColor);
footerView.setProgressColor(mProgressColor);
addView(footerView, lp);
}
}
動態響應使用者配置變化
有這樣一種需求,一個列表分頁載入,每一頁10條,如果在上拉載入更多後只返回8條,說明已經沒有更多資料了,所以在列表達到底部,使用者再次上劃時就不需要觸發上拉載入更多了。基於這種需求,我設計了一個介面NsRefreshLayoutController。
public interface NsRefreshLayoutController {
/**
* 當前下拉重新整理是否可用
*/
boolean isPullRefreshEnable();
/**
* 當前上拉載入是否可用,比如列表已無更多資料,可禁用上拉載入功能
*/
boolean isPullLoadEnable();
}
使用時,實現這個介面,根據當前資料的情況返回True或者False啟用或者禁用兩個功能了。控制元件內部,我們在使用者每次觸發觸控事件的時候獲取介面返回值。
@Override
public boolean onInterceptTouchEvent(MotionEvent ev) {
if (refreshLayoutController != null) {
mPullRefreshEnable = refreshLayoutController.isPullRefreshEnable();
mPullLoadEnable = refreshLayoutController.isPullLoadEnable();
}
return super.onInterceptTouchEvent(ev);
}
處理Touch事件
我們需要做到對Touch事件的處理不影響內容檢視的功能,所以我們只處理Touch事件,不消耗Touch事件,一個合適的回撥很重要,找來找去我選擇了dispatchTouchEvent,官方文件對這個函式的描述如下:
處理Touch事件的流程如下,ACTION_DOWN、ACTION_MOVE時記錄Touch的位置,ACTION_MOVE時用當前Touch的位置減去上次DOWN或者MOVE的位置,得到手指滑動的距離,用這個距離來控制內容檢視、重新整理檢視的顯示位置,當達到觸發重新整理的位置後,提示使用者鬆手觸發重新整理,使用者鬆手後開始重新整理動畫並通知程式開始重新整理。程式碼如下:
@Override
public boolean dispatchTouchEvent(MotionEvent event) {
if (!mPullRefreshEnable && !mPullLoadEnable) {
return super.dispatchTouchEvent(event);
}
if (isRefreshing) {
return super.dispatchTouchEvent(event);
}
switch (event.getActionMasked()) {
case MotionEvent.ACTION_DOWN: {
preY = event.getY();
preX = event.getX();
break;
}
case MotionEvent.ACTION_MOVE: {
float currentY = event.getY();
float currentX = event.getX();
float dy = currentY - preY;
float dx = currentX - preX;
preY = currentY;
preX = currentX;
if (!actionDetermined) {
//判斷是下拉重新整理還是上拉載入更多
if (dy > 0 && !canChildScrollUp() && mPullRefreshEnable) {
mCurrentAction = ACTION_PULL_DOWN_REFRESH;
actionDetermined = true;
} else if (dy < 0 && !canChildScrollDown() && mPullLoadEnable) {
mCurrentAction = ACTION_PULL_UP_LOAD_MORE;
actionDetermined = true;
}
}
handleScroll(dy);
observerArriveBottom();
break;
}
case MotionEvent.ACTION_UP:
case MotionEvent.ACTION_CANCEL: {
//使用者鬆手後需要判斷當前的滑動距離是否滿足觸發重新整理的條件
if (releaseTouch()) {
MotionEvent cancelEvent = MotionEvent.obtain(event);
cancelEvent.setAction(MotionEvent.ACTION_CANCEL);
return super.dispatchTouchEvent(cancelEvent);
}
break;
}
}
return super.dispatchTouchEvent(event);
}
/**
* 處理滾動
*/
private boolean handleScroll(float distanceY) {
if (!canChildScrollUp() && mCurrentAction == ACTION_PULL_DOWN_REFRESH &&
mPullRefreshEnable) {
//下拉重新整理
LayoutParams lp = (LayoutParams) headerView.getLayoutParams();
lp.height += distanceY;
if (lp.height < 0) {
lp.height = 0;
} else if (lp.height > loadingViewOverHeight) {
lp.height = (int) loadingViewOverHeight;
}
headerView.setLayoutParams(lp);
if (lp.height < loadingViewOverHeight) {
headerView.setLoadText(TextUtils.isEmpty(mPullRefreshText) ?
getContext().getString(R.string.default_pull_refresh_text) : mPullRefreshText);
} else {
headerView.setLoadText(getContext().getString(R.string.release_to_refresh));
}
headerView.setProgressRotation(lp.height / loadingViewOverHeight);
adjustContentViewHeight(lp.height);
return true;
} else if (!canChildScrollDown() && mCurrentAction == ACTION_PULL_UP_LOAD_MORE && mPullLoadEnable) {
//上拉載入更多
LayoutParams lp = (LayoutParams) footerView.getLayoutParams();
lp.height -= distanceY;
if (lp.height < 0) {
lp.height = 0;
} else if (lp.height > loadingViewOverHeight) {
lp.height = (int) loadingViewOverHeight;
}
footerView.setLayoutParams(lp);
if (lp.height < loadingViewOverHeight) {
footerView.setLoadText(TextUtils.isEmpty(mPullLoadText) ?
getContext().getString(R.string.default_pull_load_text) : mPullLoadText);
} else {
footerView.setLoadText(getContext().getString(R.string.release_to_load));
}
footerView.setProgressRotation(lp.height / loadingViewOverHeight);
adjustContentViewHeight(-lp.height);
return true;
}
return false;
}
private void adjustContentViewHeight(float h) {
mContentView.setTranslationY(h);
//下面的方式可以看到完整內容,但是有掉幀現象
/*if (mCurrentAction == ACTION_PULL_DOWN_REFRESH) {
mContentView.setTranslationY(h);
}
LayoutParams lp = (LayoutParams) mContentView.getLayoutParams();
lp.height = (int) (getMeasuredHeight() - Math.abs(h));
mContentView.setLayoutParams(lp);*/
}
private boolean releaseTouch() {
boolean result = false;
LayoutParams lp;
if (mPullRefreshEnable && mCurrentAction == ACTION_PULL_DOWN_REFRESH) {
lp = (LayoutParams) headerView.getLayoutParams();
if (lp.height >= loadingViewOverHeight) {
//觸發下拉重新整理
startPullDownRefresh(lp.height);
result = true;
} else if (lp.height > 0) {
//未滿足下拉重新整理觸發條件,重置狀態
resetPullDownRefresh(lp.height);
result = lp.height >= CLICK_TOUCH_DEVIATION;
} else {
resetPullRefreshState();
}
}
if (mPullLoadEnable && mCurrentAction == ACTION_PULL_UP_LOAD_MORE) {
lp = (LayoutParams) footerView.getLayoutParams();
if (lp.height >= loadingViewOverHeight) {
//觸發上拉載入更多
startPullUpLoadMore(lp.height);
result = true;
} else if (lp.height > 0) {
//未滿足上拉載入更多觸發條件,重置狀態
resetPullUpLoadMore(lp.height);
result = lp.height >= CLICK_TOUCH_DEVIATION;
} else {
resetPullLoadState();
}
}
return result;
}
private void startPullDownRefresh(int headerViewHeight) {
isRefreshing = true;
ValueAnimator animator = ValueAnimator.ofFloat(headerViewHeight, loadingViewFinalHeight);
animator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
@Override
public void onAnimationUpdate(ValueAnimator animation) {
LayoutParams lp = (LayoutParams) headerView.getLayoutParams();
lp.height = (int) ((Float) animation.getAnimatedValue()).floatValue();
headerView.setLayoutParams(lp);
adjustContentViewHeight(lp.height);
}
});
animator.addListener(new SimpleAnimatorListener() {
@Override
public void onAnimationEnd(Animator animation) {
headerView.start();
headerView.setLoadText(getContext().getString(R.string.refresh_text));
if (refreshLayoutListener != null) {
refreshLayoutListener.onRefresh();
}
}
});
animator.setDuration(300);
animator.start();
}
/**
* 重置下拉重新整理狀態
*
* @param headerViewHeight 當前下拉重新整理檢視的高度
*/
private void resetPullDownRefresh(int headerViewHeight) {
headerView.stop();
//headerView.setStartEndTrim(0, 0.75f);
ValueAnimator animator = ValueAnimator.ofFloat(headerViewHeight, 0);
animator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
@Override
public void onAnimationUpdate(ValueAnimator animation) {
LayoutParams lp = (LayoutParams) headerView.getLayoutParams();
lp.height = (int) ((Float) animation.getAnimatedValue()).floatValue();
headerView.setLayoutParams(lp);
adjustContentViewHeight(lp.height);
}
});
animator.addListener(new SimpleAnimatorListener() {
@Override
public void onAnimationEnd(Animator animation) {
resetPullRefreshState();
}
});
animator.setDuration(300);
animator.start();
}
private void resetPullRefreshState() {
//重置動畫結束才算完全完成重新整理動作
isRefreshing = false;
actionDetermined = false;
mCurrentAction = -1;
headerView.setLoadText(TextUtils.isEmpty(mPullRefreshText) ?
getContext().getString(R.string.default_pull_refresh_text) : mPullRefreshText);
}
private void startPullUpLoadMore(int headerViewHeight) {
isRefreshing = true;
ValueAnimator animator = ValueAnimator.ofFloat(headerViewHeight, loadingViewFinalHeight);
animator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
@Override
public void onAnimationUpdate(ValueAnimator animation) {
LayoutParams lp = (LayoutParams) footerView.getLayoutParams();
lp.height = (int) ((Float) animation.getAnimatedValue()).floatValue();
footerView.setLayoutParams(lp);
adjustContentViewHeight(-lp.height);
}
});
animator.addListener(new SimpleAnimatorListener() {
@Override
public void onAnimationEnd(Animator animation) {
footerView.start();
footerView.setLoadText(getContext().getString(R.string.load_text));
if (refreshLayoutListener != null) {
refreshLayoutListener.onLoadMore();
}
}
});
animator.setDuration(300);
animator.start();
}
/**
* 重置下拉重新整理狀態
*
* @param headerViewHeight 當前下拉重新整理檢視的高度
*/
private void resetPullUpLoadMore(int headerViewHeight) {
footerView.stop();
//footerView.setStartEndTrim(0.5f, 1.25f);
ValueAnimator animator = ValueAnimator.ofFloat(headerViewHeight, 0);
animator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
@Override
public void onAnimationUpdate(ValueAnimator animation) {
LayoutParams lp = (LayoutParams) footerView.getLayoutParams();
lp.height = (int) ((Float) animation.getAnimatedValue()).floatValue();
footerView.setLayoutParams(lp);
adjustContentViewHeight(-lp.height);
}
});
animator.addListener(new SimpleAnimatorListener() {
@Override
public void onAnimationEnd(Animator animation) {
resetPullLoadState();
}
});
animator.setDuration(300);
animator.start();
}
private void resetPullLoadState() {
//重置動畫結束才算完全完成重新整理動作
isRefreshing = false;
actionDetermined = false;
mCurrentAction = -1;
footerView.setLoadText(TextUtils.isEmpty(mPullLoadText) ?
getContext().getString(R.string.default_pull_load_text) : mPullLoadText);
}
/**
* @return 子檢視是否可以下拉
*/
public boolean canChildScrollUp() {
if (mContentView == null) {
return false;
}
if (Build.VERSION.SDK_INT < 14) {
if (mContentView instanceof AbsListView) {
final AbsListView absListView = (AbsListView) mContentView;
return absListView.getChildCount() > 0
&& (absListView.getFirstVisiblePosition() > 0 || absListView.getChildAt(0)
.getTop() < absListView.getPaddingTop());
} else {
return ViewCompat.canScrollVertically(mContentView, -1) || mContentView.getScrollY() > 0;
}
} else {
return ViewCompat.canScrollVertically(mContentView, -1);
}
}
/**
* @return 子檢視是否可以上劃
*/
public boolean canChildScrollDown() {
if (mContentView == null) {
return false;
}
if (Build.VERSION.SDK_INT < 14) {
if (mContentView instanceof AbsListView) {
final AbsListView absListView = (AbsListView) mContentView;
if (absListView.getChildCount() > 0) {
int lastChildBottom = absListView.getChildAt(absListView.getChildCount() - 1)
.getBottom();
return absListView.getLastVisiblePosition() == absListView.getAdapter().getCount() - 1
&& lastChildBottom <= absListView.getMeasuredHeight();
} else {
return false;
}
} else {
return ViewCompat.canScrollVertically(mContentView, 1) || mContentView.getScrollY() > 0;
}
} else {
return ViewCompat.canScrollVertically(mContentView, 1);
}
}
public void setRefreshLayoutListener(NsRefreshLayoutListener refreshLayoutListener) {
this.refreshLayoutListener = refreshLayoutListener;
}
上面程式碼中有一個變數CLICK_TOUCH_DEVIATION,這個變量表示對使用者點選事件的容錯值,使用者進行點選動作時,會產生很小的滑動距離,如果不做容錯處理會出現重新整理檢視抖動出現的問題。
另外還有一個observerArriveBottom(); 這個函式就是處理自動載入更多的關鍵。該函式在Touch事件產生滑動距離後,採取類似輪詢的機制,判斷滑動是否已經停止,滑動事件停止後,根據內容控制元件當前狀態、使用者配置來確定是否觸發載入更多事件。程式碼如下:
private void observerArriveBottom() {
if (isRefreshing || !mAutoLoadMore || !mPullLoadEnable) {
return;
}
mContentView.getViewTreeObserver().addOnScrollChangedListener(
new ViewTreeObserver.OnScrollChangedListener() {
@Override
public void onScrollChanged() {
mContentView.removeCallbacks(flingRunnable);
mContentView.postDelayed(flingRunnable, 6);
}
});
}
private Runnable flingRunnable = new Runnable() {
@Override
public void run() {
if (isRefreshing || !mAutoLoadMore || !mPullLoadEnable) {
return;
}
if (!canChildScrollDown()) {
mCurrentAction = ACTION_PULL_UP_LOAD_MORE;
isRefreshing = true;
startPullUpLoadMore(0);
}
}
};
對外介面
public interface NsRefreshLayoutListener {
void onRefresh();
void onLoadMore();
}