轉載請註明出處 http://blog.csdn.net/u011510784/article/details/50321743
Android PullToRefresh是Android應用開發中常用到的下拉刷新框架(https://github.com/chrisbanes/Android-PullToRefresh),有時候我們需要修改此開源框架以適應於自己項目的特殊需求,接下來我們分析此框架的工作流程以便定製自己所需要的控件,本文以分析PullToRefreshListView爲例,其它類似.
在分析具體實現流程之前先看幾個類:
<span style="font-family:SimHei;font-size:18px;">public abstract class LoadingLayout extends FrameLayout implements ILoadingLayout {}</span><span style="font-family:SimHei;font-size:18px;">public class RotateLoadingLayout extends LoadingLayout {
......(省略部分代碼)
public RotateLoadingLayout(Context context, Mode mode, Orientation scrollDirection, TypedArray attrs) {
super(context, mode, scrollDirection, attrs);
mRotateDrawableWhilePulling = attrs.getBoolean(R.styleable.PullToRefresh_ptrRotateDrawableWhilePulling, true);
mHeaderImage.setScaleType(ScaleType.MATRIX);
mHeaderImageMatrix = new Matrix();
mHeaderImage.setImageMatrix(mHeaderImageMatrix);
mRotateAnimation = new RotateAnimation(0, 720, Animation.RELATIVE_TO_SELF, 0.5f, Animation.RELATIVE_TO_SELF,
0.5f);
mRotateAnimation.setInterpolator(ANIMATION_INTERPOLATOR);
mRotateAnimation.setDuration(ROTATION_ANIMATION_DURATION);
mRotateAnimation.setRepeatCount(Animation.INFINITE);
mRotateAnimation.setRepeatMode(Animation.RESTART);
}
......
protected void onPullImpl(float scaleOfLayout) {
float angle;
if (mRotateDrawableWhilePulling) {
angle = scaleOfLayout * 90f;
} else {
angle = Math.max(0f, Math.min(180f, scaleOfLayout * 360f - 180f));
}
mHeaderImageMatrix.setRotate(angle, mRotationPivotX, mRotationPivotY);
mHeaderImage.setImageMatrix(mHeaderImageMatrix);
}
@Override
protected void refreshingImpl() {
mHeaderImage.startAnimation(mRotateAnimation);
}
@Override
protected void resetImpl() {
mHeaderImage.clearAnimation();
resetImageRotation();
}
private void resetImageRotation() {
if (null != mHeaderImageMatrix) {
mHeaderImageMatrix.reset();
mHeaderImage.setImageMatrix(mHeaderImageMatrix);
}
}
......
}</span>初始化了刷新動畫的屬性,並實現了刷新佈局中圖片狀態變化時所應該執行的方法,例如當用戶下拉時,刷新佈局裏面的圖片會相應的旋轉.最後一個方法是返回刷新圖片的默認ID.FlipLoadingLayout類似.
IPullToRefresh接口:
<span style="font-family:SimHei;font-size:18px;">public interface IPullToRefresh<T extends View> {
......(省略部分代碼)
//獲取當前模式
public Mode getCurrentMode();
//是否過濾掉當前的滑動事件
public boolean getFilterTouchEvents();
//獲取當前的可刷新控件,如ListView,ScrollView,ViewPager等
public T getRefreshableView();
//得到當前狀態,是正在刷新還是需要釋放等
public State getState();
//是否支持滑動刷新
public boolean isPullToRefreshEnabled();
//結束刷新
public void onRefreshComplete();
......
}</span>在IPullToRefresh接口中定義了實現下拉刷新所用到的公共方法,可以查看相應註釋.
我們看一下PullToRefreshListView的集成結構:
<span style="font-family:SimHei;font-size:18px;">public class PullToRefreshListView extends PullToRefreshAdapterViewBase<ListView>
public abstract class PullToRefreshAdapterViewBase<T extends AbsListView> extends PullToRefreshBase<T> implements OnScrollListener
public abstract class PullToRefreshBase<T extends View> extends LinearLayout implements IPullToRefresh<T> </span><span style="font-family:SimHei;font-size:18px;">public PullToRefreshBase(Context context) {
super(context);
init(context, null);
}
public PullToRefreshBase(Context context, AttributeSet attrs) {
super(context, attrs);
init(context, attrs);
}
public PullToRefreshBase(Context context, Mode mode) {
super(context);
mMode = mode;
init(context, null);
}
public PullToRefreshBase(Context context, Mode mode, AnimationStyle animStyle) {
super(context);
mMode = mode;
mLoadingAnimationStyle = animStyle;
init(context, null);
}</span>後面兩個構造方法中,Mode對象表示刷新的模式,是支持上拉還是下拉或者是都支持,AnimationStyle對象表示下拉時候的動畫效果,最後都會進入到init()方法中.
<span style="font-family:SimHei;font-size:18px;">private void init(Context context, AttributeSet attrs) {
switch (getPullToRefreshScrollDirection()) {
case HORIZONTAL:
setOrientation(LinearLayout.HORIZONTAL);
break;
case VERTICAL:
default:
setOrientation(LinearLayout.VERTICAL);
break;
}
setGravity(Gravity.CENTER);
ViewConfiguration config = ViewConfiguration.get(context);
mTouchSlop = config.getScaledTouchSlop();
// Styleables from XML
TypedArray a = context.obtainStyledAttributes(attrs, R.styleable.PullToRefresh);
......
mRefreshableView = createRefreshableView(context, attrs);
addRefreshableView(context, mRefreshableView);
// We need to create now layouts now
mHeaderLayout = createLoadingLayout(context, Mode.PULL_FROM_START, a);
mFooterLayout = createLoadingLayout(context, Mode.PULL_FROM_END, a);
......
// Let the derivative classes have a go at handling attributes, then
// recycle them...
handleStyledAttributes(a);
a.recycle();
// Finally update the UI for the modes
updateUIForMode();
}</span>首先通過getPullToRefreshScrollDirection()方法判斷當前佈局的方向,該方法爲抽象方法,在具體實現類中重寫此方法.在PullToRefreshListView類中可以找到:
<span style="font-family:SimHei;font-size:18px;"> @Override
public final Orientation getPullToRefreshScrollDirection() {
return Orientation.VERTICAL;
}</span>TypedArray a = context.obtainStyledAttributes(attrs, R.styleable.PullToRefresh);獲取自定的屬性,並將初始化默認屬性.
<span style="font-family:SimHei;font-size:18px;">mRefreshableView = createRefreshableView(context, attrs);
addRefreshableView(context, mRefreshableView);</span>createRefreshableView是抽象方法,在PullToRefreshListView中實現爲:
<span style="font-family:SimHei;font-size:18px;">@Override
protected ListView createRefreshableView(Context context, AttributeSet attrs) {
ListView lv = createListView(context, attrs);
// Set it to this so it can be used in ListActivity/ListFragment
lv.setId(android.R.id.list);
return lv;
}</span>即返回一個Listview,並將這個listview添加到PullToRefreshBase這個LinearLayout中.接下來是創建刷新的頭佈局和尾部局:
<span style="font-family:SimHei;font-size:18px;">protected LoadingLayout createLoadingLayout(Context context, Mode mode, TypedArray attrs) {
LoadingLayout layout = mLoadingAnimationStyle.createLoadingLayout(context, mode,
getPullToRefreshScrollDirection(), attrs);
layout.setVisibility(View.INVISIBLE);
return layout;
}</span>mLoadingAnimationStyle在初始化的時候已經被賦值,是一個內部類.進入到createLoadingLayout()方法中:
<span style="font-family:SimHei;font-size:18px;">LoadingLayout createLoadingLayout(Context context, Mode mode, Orientation scrollDirection, TypedArray attrs) {
switch (this) {
case ROTATE:
default:
return new RotateLoadingLayout(context, mode, scrollDirection, attrs);
case FLIP:
return new FlipLoadingLayout(context, mode, scrollDirection, attrs);
}
}</span>通過類型來創建兩種不同的刷新佈局,默認的爲ROTATE,即RotateLoadingLayout類型,這時支持的刷新的VIew(listView,scrollView等)和刷新頭尾佈局已經全部添加到此linearLayout佈局中,等待刷新動作.
那麼是如何實現下拉刷新的呢,PullToRefreshBase重寫了onInterceptTouchEvent()和onTouchEvent()方法:
<span style="font-family:SimHei;font-size:18px;">@Override
public final boolean onInterceptTouchEvent(MotionEvent event) {
if (!isPullToRefreshEnabled()) {
return false;
}
final int action = event.getAction();
if (action == MotionEvent.ACTION_CANCEL
|| action == MotionEvent.ACTION_UP) {
mIsBeingDragged = false;
return false;
}
if (action != MotionEvent.ACTION_DOWN && mIsBeingDragged) {
return true;
}
switch (action) {
case MotionEvent.ACTION_MOVE: {
// If we're refreshing, and the flag is set. Eat all MOVE events
if (!mScrollingWhileRefreshingEnabled && isRefreshing()) {
return true;
}
if (isReadyForPull()) {
final float y = event.getY(), x = event.getX();
final float diff, oppositeDiff, absDiff;
// We need to use the correct values, based on scroll
// direction
switch (getPullToRefreshScrollDirection()) {
case HORIZONTAL:
diff = x - mLastMotionX;
oppositeDiff = y - mLastMotionY;
break;
case VERTICAL:
default:
diff = y - mLastMotionY;
oppositeDiff = x - mLastMotionX;
break;
}
absDiff = Math.abs(diff);
if (absDiff > mTouchSlop
&& (!mFilterTouchEvents || absDiff > Math
.abs(oppositeDiff))) {
if (mMode.showHeaderLoadingLayout() && diff >= 1f
&& isReadyForPullStart()) {
mLastMotionY = y;
mLastMotionX = x;
mIsBeingDragged = true;
if (mMode == Mode.BOTH) {
mCurrentMode = Mode.PULL_FROM_START;
}
} else if (mMode.showFooterLoadingLayout() && diff <= -1f
&& isReadyForPullEnd()) {
mLastMotionY = y;
mLastMotionX = x;
mIsBeingDragged = true;
if (mMode == Mode.BOTH) {
mCurrentMode = Mode.PULL_FROM_END;
}
}
}
}
break;
}
case MotionEvent.ACTION_DOWN: {
if (isReadyForPull()) {
mLastMotionY = mInitialMotionY = event.getY();
mLastMotionX = mInitialMotionX = event.getX();
mIsBeingDragged = false;
}
break;
}
}
return mIsBeingDragged;
}</span>在事件攔截方法中判斷是否需要攔截此次的滑動事件.重點看ACTION_MOVE裏面的代碼,這裏有判斷條件叫isReadyForPull(),顧名思義,當前view是否準備好要刷新了,也就是view是否滑到了頂部:
<span style="font-family:SimHei;font-size:18px;"> private boolean isReadyForPull() {
switch (mMode) {
case PULL_FROM_START:
return isReadyForPullStart();
case PULL_FROM_END:
return isReadyForPullEnd();
case BOTH:
return isReadyForPullEnd() || isReadyForPullStart();
default:
return false;
}
}</span>根據不同的判斷條件執行了相應的方法,執行的方法是抽象方法,我們看一下其子類是如何實現這些抽象方法的,在PullToRefreshAdapterViewBase中我們可以找到:
<span style="font-family:SimHei;font-size:18px;">protected boolean isReadyForPullStart() {
return isFirstItemVisible();
}
protected boolean isReadyForPullEnd() {
return isLastItemVisible();
}</span>和我們預想的一樣,在sFirstItemVisible()方法中具體判斷了是否此view滑到了頂部.接着回到ACTION_MOVE滑動事件中,當isReadyForPull()返回true時,計算一些滑動的數據後,mIsBeingDragged被賦值爲true,即onInterceptTouchEvent()返回true,事件被攔截,交給onTouchEvent()方法:
<span style="font-family:SimHei;font-size:18px;">@Override
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();
return true;
}
break;
}
case MotionEvent.ACTION_DOWN: {
if (isReadyForPull()) {
mLastMotionY = mInitialMotionY = event.getY();
mLastMotionX = mInitialMotionX = event.getX();
return true;
}
break;
}
case MotionEvent.ACTION_CANCEL:
case MotionEvent.ACTION_UP: {
if (mIsBeingDragged) {
mIsBeingDragged = false;
if (mState == State.RELEASE_TO_REFRESH
&& (null != mOnRefreshListener || null != mOnRefreshListener2)) {
setState(State.REFRESHING, true);
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);
return true;
}
break;
}
}
return false;
}</span>先看一下ACTION_MOVE事件,計算完一些滑動的數據後,進入了pullEvent()方法:
<pre name="code" class="html"> ...... 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);
break;
}
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);
}
}
......</pre><pre><span style="font-family:SimHei;font-size:18px;">protected final void setHeaderScroll(int value) {
......
switch (getPullToRefreshScrollDirection()) {
case VERTICAL:
scrollTo(0, value);
break;
case HORIZONTAL:
<span style="font-family: Arial, Helvetica, sans-serif;">scrollTo</span><span style="font-family: Arial, Helvetica, sans-serif;">(value, 0);</span>
break;
}
}
</span><span style="font-family:SimHei;font-size:18px;"> public final void onPull(float scaleOfLayout) {
if (!mUseIntrinsicAnimation) {
onPullImpl(scaleOfLayout);
}
}</span><span style="font-family:SimHei;font-size:18px;">protected void onPullImpl(float scaleOfLayout) {
float angle;
if (mRotateDrawableWhilePulling) {
angle = scaleOfLayout * 90f;
} else {
angle = Math.max(0f, Math.min(180f, scaleOfLayout * 360f - 180f));
}
mHeaderImageMatrix.setRotate(angle, mRotationPivotX, mRotationPivotY);
mHeaderImage.setImageMatrix(mHeaderImageMatrix);
}</span><span style="font-family:SimHei;font-size:18px;">case MotionEvent.ACTION_UP: {
if (mIsBeingDragged) {
mIsBeingDragged = false;
if (mState == State.RELEASE_TO_REFRESH
&& (null != mOnRefreshListener || null != mOnRefreshListener2)) {
setState(State.REFRESHING, true);
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);
return true;
}
break;
}</span><span style="font-family:SimHei;font-size:18px;">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();
}
};
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);
}
} else {
// We're not scrolling, so just call Refresh Listener now
callRefreshListener();
}
}</span>在這裏設置正在刷新的狀態,並執行用戶的刷新方法,當用戶的刷新方法執行完後調用mPullRefreshListView.onRefreshComplete();最終會調用:
<span style="font-family:SimHei;font-size:18px;">protected void onReset() {
mIsBeingDragged = false;
mLayoutVisibilityChangesEnabled = true;
// Always reset both layouts, just in case...
mHeaderLayout.reset();
mFooterLayout.reset();
smoothScrollTo(0);
}</span>