5.3.2 开源Android-PullToRefresh下拉刷新源码分析

 

开源Android-PullToRefresh下拉刷新源码分析

标签： Android布局下拉刷新pullToRefresh源码

2015-04-02 14:48  2448人阅读  评论(1)  收藏  举报

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Android 技术研究（39） 

版权声明：本文为博主原创文章，未经博主允许不得转载。

  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。