Android基于ViewFlipper實現(xiàn)圖片切換
[導(dǎo)讀]在很多App上我們經(jīng)常看到這些效果：淘寶首頁自動滾動的圖片展示效果支付寶應(yīng)用第一次啟動啟動的用戶引導(dǎo)畫面要實現(xiàn)這些效果，有些控件可以幫助我們：1. ViewPager2. ViewFlipper3.
在很多App上我們經(jīng)?？吹竭@些效果：
淘寶首頁自動滾動的圖片展示效果支付寶應(yīng)用第一次啟動啟動的用戶引導(dǎo)畫面
要實現(xiàn)這些效果，有些控件可以幫助我們：
1. ViewPager
2. ViewFlipper
3. Fragment
好吧，我最終選擇了ViewFlipper，因為它的使用最干勁清爽（往里面放幾個View就行了），而且還支持自動播放。
不過，為了實現(xiàn)上面兩個效果，還得解決來年兩個問題：
1. 如何在ViewFlipper滾動的時候，獲得當前展示的child id？
2. 和ViewPager原生支持觸摸滑動翻頁不同，ViewFlipper需要自己監(jiān)聽手勢來解決。
問題1：其實，我挺奇怪的，Google既然為ViewAnimation做了個ViewFlipper的子類來支持自動翻滾，怎么不給它添加一個listener以監(jiān)聽翻滾事件呢？
好吧，既然google不給，那就自己加。首先看ViewFlipper的源碼（
/*
?*?Copyright?(C)?2006?The?Android?Open?Source?Project
?*
?*?Licensed?under?the?Apache?License,?Version?2.0?(the?"License");
?*?you?may?not?use?this?file?except?in?compliance?with?the?License.
?*?You?may?obtain?a?copy?of?the?License?at
?*
?*??????http://www.apache.org/licenses/LICENSE-2.0
?*
?*?Unless?required?by?applicable?law?or?agreed?to?in?writing,?software
?*?distributed?under?the?License?is?distributed?on?an?"AS?IS"?BASIS,
?*?WITHOUT?WARRANTIES?OR?CONDITIONS?OF?ANY?KIND,?either?express?or?implied.
?*?See?the?License?for?the?specific?language?governing?permissions?and
?*?limitations?under?the?License.
?*/
package?android.widget;
import?android.content.BroadcastReceiver;
import?android.content.Context;
import?android.content.Intent;
import?android.content.IntentFilter;
import?android.content.res.TypedArray;
import?android.os.Handler;
import?android.os.Message;
import?android.util.AttributeSet;
import?android.util.Log;
import?android.view.accessibility.AccessibilityEvent;
import?android.view.accessibility.AccessibilityNodeInfo;
import?android.widget.RemoteViews.RemoteView;
/**
?*?Simple?{@link?ViewAnimator}?that?will?animate?between?two?or?more?views
?*?that?have?been?added?to?it.??Only?one?child?is?shown?at?a?time.??If
?*?requested,?can?automatically?flip?between?each?child?at?a?regular?interval.
?*
?*?@attr?ref?android.R.styleable#ViewFlipper_flipInterval
?*?@attr?ref?android.R.styleable#ViewFlipper_autoStart
?*/
@RemoteView
public?class?ViewFlipper?extends?ViewAnimator?{
????private?static?final?String?TAG?=?"ViewFlipper";
????private?static?final?boolean?LOGD?=?false;
????private?static?final?int?DEFAULT_INTERVAL?=?3000;
????private?int?mFlipInterval?=?DEFAULT_INTERVAL;
????private?boolean?mAutoStart?=?false;
????private?boolean?mRunning?=?false;
????private?boolean?mStarted?=?false;
????private?boolean?mVisible?=?false;
????private?boolean?mUserPresent?=?true;
????public?ViewFlipper(Context?context)?{
????????super(context);
????}
????public?ViewFlipper(Context?context,?AttributeSet?attrs)?{
????????super(context,?attrs);
????????TypedArray?a?=?context.obtainStyledAttributes(attrs,
????????????????com.android.internal.R.styleable.ViewFlipper);
????????mFlipInterval?=?a.getInt(
????????????????com.android.internal.R.styleable.ViewFlipper_flipInterval,?DEFAULT_INTERVAL);
????????mAutoStart?=?a.getBoolean(
????????????????com.android.internal.R.styleable.ViewFlipper_autoStart,?false);
????????a.recycle();
????}
????private?final?BroadcastReceiver?mReceiver?=?new?BroadcastReceiver()?{
????????@Override
????????public?void?onReceive(Context?context,?Intent?intent)?{
????????????final?String?action?=?intent.getAction();
????????????if?(Intent.ACTION_SCREEN_OFF.equals(action))?{
????????????????mUserPresent?=?false;
????????????????updateRunning();
????????????}?else?if?(Intent.ACTION_USER_PRESENT.equals(action))?{
????????????????mUserPresent?=?true;
????????????????updateRunning(false);
????????????}
????????}
????};
????@Override
????protected?void?onAttachedToWindow()?{
????????super.onAttachedToWindow();
????????//?Listen?for?broadcasts?related?to?user-presence
????????final?IntentFilter?filter?=?new?IntentFilter();
????????filter.addAction(Intent.ACTION_SCREEN_OFF);
????????filter.addAction(Intent.ACTION_USER_PRESENT);
????????getContext().registerReceiver(mReceiver,?filter);
????????if?(mAutoStart)?{
????????????//?Automatically?start?when?requested
????????????startFlipping();
????????}
????}
????@Override
????protected?void?onDetachedFromWindow()?{
????????super.onDetachedFromWindow();
????????mVisible?=?false;
????????getContext().unregisterReceiver(mReceiver);
????????updateRunning();
????}
????@Override
????protected?void?onWindowVisibilityChanged(int?visibility)?{
????????super.onWindowVisibilityChanged(visibility);
????????mVisible?=?visibility?==?VISIBLE;
????????updateRunning(false);
????}
????/**
?????*?How?long?to?wait?before?flipping?to?the?next?view
?????*
?????*?@param?milliseconds
?????*????????????time?in?milliseconds
?????*/
????@android.view.RemotableViewMethod
????public?void?setFlipInterval(int?milliseconds)?{
????????mFlipInterval?=?milliseconds;
????}
????/**
?????*?Start?a?timer?to?cycle?through?child?views
?????*/
????public?void?startFlipping()?{
????????mStarted?=?true;
????????updateRunning();
????}
????/**
?????*?No?more?flips
?????*/
????public?void?stopFlipping()?{
????????mStarted?=?false;
????????updateRunning();
????}
????@Override
????public?void?onInitializeAccessibilityEvent(AccessibilityEvent?event)?{
????????super.onInitializeAccessibilityEvent(event);
????????event.setClassName(ViewFlipper.class.getName());
????}
????@Override
????public?void?onInitializeAccessibilityNodeInfo(AccessibilityNodeInfo?info)?{
????????super.onInitializeAccessibilityNodeInfo(info);
????????info.setClassName(ViewFlipper.class.getName());
????}
????/**
?????*?Internal?method?to?start?or?stop?dispatching?flip?{@link?Message}?based
?????*?on?{@link?#mRunning}?and?{@link?#mVisible}?state.
?????*/
????private?void?updateRunning()?{
????????updateRunning(true);
????}
????/**
?????*?Internal?method?to?start?or?stop?dispatching?flip?{@link?Message}?based
?????*?on?{@link?#mRunning}?and?{@link?#mVisible}?state.
?????*
?????*?@param?flipNow?Determines?whether?or?not?to?execute?the?animation?now,?in
?????*????????????addition?to?queuing?future?flips.?If?omitted,?defaults?to
?????*????????????true.
?????*/
????private?void?updateRunning(boolean?flipNow)?{
????????boolean?running?=?mVisible?&&?mStarted?&&?mUserPresent;
????????if?(running?!=?mRunning)?{
????????????if?(running)?{
????????????????showOnly(mWhichChild,?flipNow);
????????????????Message?msg?=?mHandler.obtainMessage(FLIP_MSG);
????????????????mHandler.sendMessageDelayed(msg,?mFlipInterval);
????????????}?else?{
????????????????mHandler.removeMessages(FLIP_MSG);
????????????}
????????????mRunning?=?running;
????????}
????????if?(LOGD)?{
????????????Log.d(TAG,?"updateRunning()?mVisible="?+?mVisible?+?",?mStarted="?+?mStarted
????????????????????+?",?mUserPresent="?+?mUserPresent?+?",?mRunning="?+?mRunning);
????????}
????}
????/**
?????*?Returns?true?if?the?child?views?are?flipping.
?????*/
????public?boolean?isFlipping()?{
????????return?mStarted;
????}
????/**
?????*?Set?if?this?view?automatically?calls?{@link?#startFlipping()}?when?it
?????*?becomes?attached?to?a?window.
?????*/
????public?void?setAutoStart(boolean?autoStart)?{
????????mAutoStart?=?autoStart;
????}
????/**
?????*?Returns?true?if?this?view?automatically?calls?{@link?#startFlipping()}
?????*?when?it?becomes?attached?to?a?window.
?????*/
????public?boolean?isAutoStart()?{
????????return?mAutoStart;
????}
????private?final?int?FLIP_MSG?=?1;
????private?final?Handler?mHandler?=?new?Handler()?{
????????@Override
????????public?void?handleMessage(Message?msg)?{
????????????if?(msg.what?==?FLIP_MSG)?{
????????????????if?(mRunning)?{
????????????????????showNext();
????????????????????msg?=?obtainMessage(FLIP_MSG);
????????????????????sendMessageDelayed(msg,?mFlipInterval);
????????????????}
????????????}
????????}
????};
}
代碼還是挺簡單易懂的，就是用了一個Handler來定時調(diào)用showNext()。
可惜，mHandler成員是private+final的，我們無法改動它了。
不過，既然ViewFlipper不是一個final類，那就好辦，自定義類繼承ViewFlipper,重載showNext（）函數(shù)：
package?com.example.viewflipper;
import?android.widget.ViewFlipper;
/**
?*?Created?by?ray?on?7/4/13.
?*/
public?class?MyViewFilpper?extends?ViewFlipper?{
????private?OnDisplayChagnedListener?mListener;
????public?MyViewFilpper(android.content.Context?context)?{
????????super(context);
????}
????public?MyViewFilpper(android.content.Context?context,?android.util.AttributeSet?attrs)?{
????????super(context,?attrs);
????}
????public?void?setOnDisplayChagnedListener(OnDisplayChagnedListener?listener)?{
????????if?(mListener?!=?listener)?{
????????????this.mListener?=?listener;
????????}
????}
????@Override
????public?void?showNext()?{
????????super.showNext();
????????if(mListener?!=?null){
????????????mListener.OnDisplayChildChanging(this,?super.getDisplayedChild());
????????}
????}
????@Override
????public?void?showPrevious()?{
????????super.showPrevious();
????????if(mListener?!=?null){
????????????mListener.OnDisplayChildChanging(this,?super.getDisplayedChild());
????????}
????}
????public?interface?OnDisplayChagnedListener?{
????????void?OnDisplayChildChanging(ViewFlipper?view,?int?index);
????}
}問題2，就比較好解決了，OnTouchListener + GestureDetector 監(jiān)聽flipper事件，這里就不貼代碼了。
好吧，這樣基本問題都被解決了，為了讓效果好一點，又給ViewFlipper加上了進入動畫和離開動畫。
好吧，下方的1，2，3有點難看，大家湊合下。
當目前為止，本人對效果還算滿意，但是，還存在兩個問題：
1. 沒有處理GestureDetectorListener的onScroll函數(shù)，也就是說，在用戶的手指離開屏幕前，不會有滾動效果。
2. 因為是通GestureDetector是通過TouchListener工作的,作為一個容器，如果內(nèi)部元素消耗掉了touch事件，則touchlistener無法工作，手勢的監(jiān)聽自然也無從談起。不過，僅僅是應(yīng)付圖片瀏覽的話，還是有辦法解決的：
a. 對于用戶引導(dǎo)這樣的場景，圖片展示是不會消耗touch消息的。
b. 而淘寶首頁的圖片動態(tài)則不同，在用戶點擊圖片的時候，把頁面轉(zhuǎn)到商品的展示頁面，這種情況下，一般會考慮使用ImageButton控件來處理Click事件，這樣就導(dǎo)致手勢無法監(jiān)聽。解決方案是，仍舊使用ImageVIew控件，但是在GestureListener的OnSingleTapUp事件上，獲取當前展示的頁面，然后根據(jù)頁面信息轉(zhuǎn)到商品展示頁面。
但是，如果是一些比較復(fù)雜的情況，就比較難處理，雖然通過重載onInterceptTouchEvent函數(shù)，父容器也能監(jiān)聽所有由子控件消耗的消息，但是也可能存在一些邏輯問題：例如在ViewFlipper容器內(nèi)包含了一個Gallary控件，那scroll消息應(yīng)該由哪個控件來處理，亦或都處理？這就是個比較費腦筋的問題了，設(shè)計UI的時候，可以考慮設(shè)計的簡單些。
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