Android Path Time ScrollBar（Path 时间轴）

版本：1.0

日期：2014.4.22

版权：© 2014 kince 转载注明出处

  这是仿Path2.0UI的一个demo的截图，我最早是在农民伯伯的这篇博客中看到的 【Andorid X 项目笔记】开源项目使用（6） ，他说这个程序是反编译Path的，但是这次我特地看了一下代码，发现其实不是这样的。原帖地址应该是这个： http://www.eoeandroid.com/forum.php?mod=viewthread&tid=187725 ，作者使用的是github上的一个开源项目： Android-ScrollBarPanel ，它实现的效果如下：

  已经很接近Path的效果了，还有墨迹天气的实景也是使用了这种效果：

  而且，墨迹天气用的也是这个开源项目，效果什么基本都没改。所以下面重点说一下这个开源项目的实现。在看它的代码之前先来分析一下这个效果该如何实现，它就是在滚动条（ scrollbar） 的旁边动态显示一个View，这个View里面显示的内容会随着滚动条的位置变化而变化。一般像带滑动效果的容器控制都会有滚动条，比如ScrollView、ListView、GeidView等。那这个滚动条到底是什么呢？它是一个View的属性，该属性是继承view的， 目的设置滚动条显示，有以下设置none（隐藏），horizontal（水平），vertical （垂直），并不是所有的view设置就有效果， LinearLayout 设置也没有效果， 要想在超过一屏时拖动效果，在最外层加上ScrollView。而且可以自定义滚动条的样式和位置。但Path用的并不是自定义的滚动条，它是在滚动条旁边加的View，如图：

   若是在滚动条的旁边添加显示View，首先需要获取滚动条的位置，当在滑动的时候在显示滚动条的同时也让添加的View显示出来，也就是说它和滚动条的显示是同步的。那到底如何实现呢，带着这些疑问看一下源码：

package com.dafruits.android.library.widgets;

import android.content.Context;
import android.content.res.TypedArray;
import android.graphics.Canvas;
import android.os.Handler;
import android.util.AttributeSet;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewConfiguration;
import android.view.animation.Animation;
import android.view.animation.Animation.AnimationListener;
import android.view.animation.AnimationUtils;
import android.widget.AbsListView;
import android.widget.AbsListView.OnScrollListener;
import android.widget.ListView;

import com.dafruits.android.library.R;

public class ExtendedListView extends ListView implements OnScrollListener {

     public static interface OnPositionChangedListener {

          public void onPositionChanged(ExtendedListView listView, int position, View scrollBarPanel);

     }

     private OnScrollListener mOnScrollListener = null;

     private View mScrollBarPanel = null;
     private int mScrollBarPanelPosition = 0;

     private OnPositionChangedListener mPositionChangedListener;
     private int mLastPosition = -1;

     private Animation mInAnimation = null;
     private Animation mOutAnimation = null;

     private final Handler mHandler = new Handler();

     private final Runnable mScrollBarPanelFadeRunnable = new Runnable() {

          @Override
          public void run() {
               if (mOutAnimation != null) {
                    mScrollBarPanel.startAnimation(mOutAnimation);
               }
          }
     };

     /*
     * keep track of Measure Spec
     */
     private int mWidthMeasureSpec;
     private int mHeightMeasureSpec;

     public ExtendedListView(Context context) {
          this(context, null);
     }

     public ExtendedListView(Context context, AttributeSet attrs) {
          this(context, attrs, android.R.attr.listViewStyle);
     }

     public ExtendedListView(Context context, AttributeSet attrs, int defStyle) {
          super(context, attrs, defStyle);

          super.setOnScrollListener(this);

          final TypedArray a = context.obtainStyledAttributes(attrs, R.styleable.ExtendedListView);
          final int scrollBarPanelLayoutId = a.getResourceId(R.styleable.ExtendedListView_scrollBarPanel, -1);
          final int scrollBarPanelInAnimation = a.getResourceId(R.styleable.ExtendedListView_scrollBarPanelInAnimation, R.anim.in_animation);
          final int scrollBarPanelOutAnimation = a.getResourceId(R.styleable.ExtendedListView_scrollBarPanelOutAnimation, R.anim.out_animation);
          a.recycle();

          if (scrollBarPanelLayoutId != -1) {
               setScrollBarPanel(scrollBarPanelLayoutId);
          }

          final int scrollBarPanelFadeDuration = ViewConfiguration.getScrollBarFadeDuration();

          if (scrollBarPanelInAnimation > 0) {
               mInAnimation = AnimationUtils.loadAnimation(getContext(), scrollBarPanelInAnimation);
          }
         
          if (scrollBarPanelOutAnimation > 0) {
               mOutAnimation = AnimationUtils.loadAnimation(getContext(), scrollBarPanelOutAnimation);
               mOutAnimation.setDuration(scrollBarPanelFadeDuration);

               mOutAnimation.setAnimationListener(new AnimationListener() {

                    @Override
                    public void onAnimationStart(Animation animation) {
                    }

                    @Override
                    public void onAnimationRepeat(Animation animation) {

                    }

                    @Override
                    public void onAnimationEnd(Animation animation) {
                         if (mScrollBarPanel != null) {
                              mScrollBarPanel.setVisibility(View.GONE);
                         }
                    }
               });
          }
     }

     @Override
     public void onScrollStateChanged(AbsListView view, int scrollState) {
          if (mOnScrollListener != null) {
               mOnScrollListener.onScrollStateChanged(view, scrollState);
          }
     }

     @Override
     public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) {
          if (null != mPositionChangedListener && null != mScrollBarPanel) {

               // Don't do anything if there is no itemviews
               if (totalItemCount > 0) {
                    /*
                    * from android source code (ScrollBarDrawable.java)
                    */
                    final int thickness = getVerticalScrollbarWidth();
                    int height = Math.round((float) getMeasuredHeight() * computeVerticalScrollExtent() / computeVerticalScrollRange());
                    int thumbOffset = Math.round((float) (getMeasuredHeight() - height) * computeVerticalScrollOffset() / (computeVerticalScrollRange() - computeVerticalScrollExtent()));
                    final int minLength = thickness * 2;
                    if (height < minLength) {
                         height = minLength;
                    }
                    thumbOffset += height / 2;
                   
                    /*
                    * find out which itemviews the center of thumb is on
                    */
                    final int count = getChildCount();
                    for (int i = 0; i < count; ++i) {
                         final View childView = getChildAt(i);
                         if (childView != null) {
                              if (thumbOffset > childView.getTop() && thumbOffset < childView.getBottom()) {
                                   /*
                                   * we have our candidate
                                   */
                                   if (mLastPosition != firstVisibleItem + i) {
                                        mLastPosition = firstVisibleItem + i;
                                       
                                        /*
                                        * inform the position of the panel has changed
                                        */
                                        mPositionChangedListener.onPositionChanged(this, mLastPosition, mScrollBarPanel);
                                       
                                        /*
                                        * measure panel right now since it has just changed
                                        *
                                        * INFO: quick hack to handle TextView has ScrollBarPanel (to wrap text in
                                        * case TextView's content has changed)
                                        */
                                        measureChild(mScrollBarPanel, mWidthMeasureSpec, mHeightMeasureSpec);
                                   }
                                   break;
                              }
                         }
                    }

                    /*
                    * update panel position
                    */
                    mScrollBarPanelPosition = thumbOffset - mScrollBarPanel.getMeasuredHeight() / 2;
                    final int x = getMeasuredWidth() - mScrollBarPanel.getMeasuredWidth() - getVerticalScrollbarWidth();
                    mScrollBarPanel.layout(x, mScrollBarPanelPosition, x + mScrollBarPanel.getMeasuredWidth(),
                              mScrollBarPanelPosition + mScrollBarPanel.getMeasuredHeight());
               }
          }

          if (mOnScrollListener != null) {
               mOnScrollListener.onScroll(view, firstVisibleItem, visibleItemCount, totalItemCount);
          }
     }

     public void setOnPositionChangedListener(OnPositionChangedListener onPositionChangedListener) {
          mPositionChangedListener = onPositionChangedListener;
     }

     @Override
     public void setOnScrollListener(OnScrollListener onScrollListener) {
          mOnScrollListener = onScrollListener;
     }

     public void setScrollBarPanel(View scrollBarPanel) {
          mScrollBarPanel = scrollBarPanel;
          mScrollBarPanel.setVisibility(View.GONE);
          requestLayout();
     }

     public void setScrollBarPanel(int resId) {
          setScrollBarPanel(LayoutInflater.from(getContext()).inflate(resId, this, false));
     }

     public View getScrollBarPanel() {
          return mScrollBarPanel;
     }
    
     @Override
     protected boolean awakenScrollBars(int startDelay, boolean invalidate) {
          final boolean isAnimationPlayed = super.awakenScrollBars(startDelay, invalidate);
         
          if (isAnimationPlayed == true && mScrollBarPanel != null) {
               if (mScrollBarPanel.getVisibility() == View.GONE) {
                    mScrollBarPanel.setVisibility(View.VISIBLE);
                    if (mInAnimation != null) {
                         mScrollBarPanel.startAnimation(mInAnimation);
                    }
               }
              
               mHandler.removeCallbacks(mScrollBarPanelFadeRunnable);
               mHandler.postAtTime(mScrollBarPanelFadeRunnable, AnimationUtils.currentAnimationTimeMillis() + startDelay);
          }

          return isAnimationPlayed;
     }

     @Override
     protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
          super.onMeasure(widthMeasureSpec, heightMeasureSpec);

          if (mScrollBarPanel != null && getAdapter() != null) {
               mWidthMeasureSpec = widthMeasureSpec;
               mHeightMeasureSpec = heightMeasureSpec;
               measureChild(mScrollBarPanel, widthMeasureSpec, heightMeasureSpec);
          }
     }

     @Override
     protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
          super.onLayout(changed, left, top, right, bottom);

          if (mScrollBarPanel != null) {
               final int x = getMeasuredWidth() - mScrollBarPanel.getMeasuredWidth() - getVerticalScrollbarWidth();
               mScrollBarPanel.layout(x, mScrollBarPanelPosition, x + mScrollBarPanel.getMeasuredWidth(),
                         mScrollBarPanelPosition + mScrollBarPanel.getMeasuredHeight());
          }
     }

     @Override
     protected void dispatchDraw(Canvas canvas) {
          super.dispatchDraw(canvas);

          if (mScrollBarPanel != null && mScrollBarPanel.getVisibility() == View.VISIBLE) {
               drawChild(canvas, mScrollBarPanel, getDrawingTime());
          }
     }

     @Override
     public void onDetachedFromWindow() {
          super.onDetachedFromWindow();

          mHandler.removeCallbacks(mScrollBarPanelFadeRunnable);
     }
}

   通过阅读源码发现，这是一个自定义的ListView，并且继承了OnScrollListener接口，这个接口是在AbsListView.java里面定义的，主要是负责滑动事件的处理，它的代码如下：

 /**
     * Interface definition for a callback to be invoked when the list or grid
     * has been scrolled.
     */
    public interface OnScrollListener {

        /**
         * The view is not scrolling. Note navigating the list using the trackball counts as
         * being in the idle state since these transitions are not animated.
         */
        public static int SCROLL_STATE_IDLE = 0;

        /**
         * The user is scrolling using touch, and their finger is still on the screen
         */
        public static int SCROLL_STATE_TOUCH_SCROLL = 1;

        /**
         * The user had previously been scrolling using touch and had performed a fling. The
         * animation is now coasting to a stop
         */
        public static int SCROLL_STATE_FLING = 2;

        /**
         * Callback method to be invoked while the list view or grid view is being scrolled. If the
         * view is being scrolled, this method will be called before the next frame of the scroll is
         * rendered. In particular, it will be called before any calls to
         * {@link Adapter#getView(int, View, ViewGroup)}.
         *
         * @param view The view whose scroll state is being reported
         *
         * @param scrollState The current scroll state. One of {@link #SCROLL_STATE_IDLE},
         * {@link #SCROLL_STATE_TOUCH_SCROLL} or {@link #SCROLL_STATE_IDLE}.
         */
        public void onScrollStateChanged(AbsListView view, int scrollState);

        /**
         * Callback method to be invoked when the list or grid has been scrolled. This will be
         * called after the scroll has completed
         * @param view The view whose scroll state is being reported
         * @param firstVisibleItem the index of the first visible cell (ignore if
         *        visibleItemCount == 0)
         * @param visibleItemCount the number of visible cells
         * @param totalItemCount the number of items in the list adaptor
         */
        public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount,
                int totalItemCount);
    }

   OnScrollListener定义了三个常量，分别表示当屏幕停止滚动时为0；当屏幕滚动且用户使用的触碰或手指还在屏幕上时为1；由于用户的操作，屏幕产生惯性滑动时为2。具体解释如下：

new OnScrollListener() {   
        boolean isLastRow = false;   
       
        @Override   
        public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) {   
            //滚动时一直回调，直到停止滚动时才停止回调。单击时回调一次。   
            //firstVisibleItem：当前能看见的第一个列表项ID（从0开始）   
            //visibleItemCount：当前能看见的列表项个数（小半个也算）   
            //totalItemCount：列表项共数   
       
            //判断是否滚到最后一行   
            if (firstVisibleItem + visibleItemCount == totalItemCount && totalItemCount > 0) {   
                isLastRow = true;   
            }   
        }   
        @Override   
        public void onScrollStateChanged(AbsListView view, int scrollState) {   
            //正在滚动时回调，回调2-3次，手指没抛则回调2次。scrollState = 2的这次不回调   
            //回调顺序如下   
            //第1次：scrollState = SCROLL_STATE_TOUCH_SCROLL(1) 正在滚动   
            //第2次：scrollState = SCROLL_STATE_FLING(2) 手指做了抛的动作（手指离开屏幕前，用力滑了一下）   
            //第3次：scrollState = SCROLL_STATE_IDLE(0) 停止滚动            
            //当屏幕停止滚动时为0；当屏幕滚动且用户使用的触碰或手指还在屏幕上时为1； 
            //由于用户的操作，屏幕产生惯性滑动时为2 
       
            //当滚到最后一行且停止滚动时，执行加载   
            if (isLastRow && scrollState == AbsListView.OnScrollListener.SCROLL_STATE_IDLE) {   
                //加载元素   
                ......   
       
                isLastRow = false;   
            }   
        }   
    } 

   了解完OnScrollListener这个接口再回头看一下代码，首先定义了一个回调：

   public static interface OnPositionChangedListener {

          public void onPositionChanged(ExtendedListView listView, int position,
                    View scrollBarPanel);

     }

  这个用来在Activity中设置监听事件的，Activity的代码如下：

package com.dafruits.android.samples;

import android.app.Activity;
import android.graphics.Color;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.TextView;

import com.dafruits.android.library.widgets.ExtendedListView;
import com.dafruits.android.library.widgets.ExtendedListView.OnPositionChangedListener;

public class DemoScrollBarPanelActivity extends Activity implements OnPositionChangedListener {

     private ExtendedListView mListView;

     @Override
     public void onCreate(Bundle savedInstanceState) {
          super.onCreate(savedInstanceState);

          setContentView(R.layout.main);

          mListView = (ExtendedListView) findViewById(android.R.id.list);
          mListView.setAdapter(new DummyAdapter());
          mListView.setCacheColorHint(Color.TRANSPARENT);
          mListView.setOnPositionChangedListener(this);
     }

     private class DummyAdapter extends BaseAdapter {

          private int mNumDummies = 100;

          @Override
          public int getCount() {
               return mNumDummies;
          }

          @Override
          public Object getItem(int position) {
               return position;
          }

          @Override
          public long getItemId(int position) {
               return position;
          }

          @Override
          public View getView(int position, View convertView, ViewGroup parent) {
               if (convertView == null) {
                    convertView = LayoutInflater.from(DemoScrollBarPanelActivity.this).inflate(R.layout.list_item, parent,
                              false);
               }

               TextView textView = (TextView) convertView;
               textView.setText("" + position);

               return convertView;
          }
     }

     @Override
     public void onPositionChanged(ExtendedListView listView, int firstVisiblePosition, View scrollBarPanel) {
          ((TextView) scrollBarPanel).setText("Position " + firstVisiblePosition);
     }
}

  接着看一下第三个构造方法，因为这个自定义的ListView定义了自己的属性，所以需要从attrs文件中来取出这些属性，自定义的属性包括三个部分，一是在ListView滑动时弹出的View，二是这个View弹出时的动画，三是这个View消失时的动画。然后开始设置这个弹出的View：

  if (scrollBarPanelLayoutId != -1) {
               setScrollBarPanel(scrollBarPanelLayoutId);
          }

   看一下设置的方法，

  public void setScrollBarPanel(View scrollBarPanel) {
          mScrollBarPanel = scrollBarPanel;
          mScrollBarPanel.setVisibility(View.GONE);
          requestLayout();
     }

     public void setScrollBarPanel(int resId) {
          setScrollBarPanel(LayoutInflater.from(getContext()).inflate(resId,
                    this, false));
     }

  

  先是调用下面这个方法，从xml文件中加载弹出View的布局，在这个地方需要说一下如果自定义的View不需要手动绘制的话，那么就可以使用LayoutInflater去在xml中加载一个已经配置好的视图，本例中就是使用这个方式。这样mScrollBarPanel就储存了弹出的View，然后设置为不可见，使用requestLayout()刷新一下视图。再接着就是加载两个弹出的动画，特别的，在mOutAnimation动画中设置了监听器，在动画结束的时候设置弹出的View不可见。

  回到第三个构造方法中，在第二行设置了super.setOnScrollListener(this)，这个方法是效果实现的关键，为什么这么说，先看一下它的源代码。它是在AbsListView中定义的，

   /**
     * Set the listener that will receive notifications every time the list scrolls.
     *
     * @param l the scroll listener
     */
    public void setOnScrollListener(OnScrollListener l) {
        mOnScrollListener = l;
        invokeOnItemScrollListener();
    }

  设置这个方法后，会传递一个 OnScrollListener对象给 mOnScrollListener，然后调用 invokeOnItemScrollListener()方法，它的代码如下：

 /**
     * Notify our scroll listener (if there is one) of a change in scroll state
     */
    void invokeOnItemScrollListener() {
        if (mFastScroller != null) {
            mFastScroller.onScroll(this, mFirstPosition, getChildCount(), mItemCount);
        }
        if (mOnScrollListener != null) {
            mOnScrollListener.onScroll(this, mFirstPosition, getChildCount(), mItemCount);
        }
        onScrollChanged(0, 0, 0, 0); // dummy values, View's implementation does not use these.
    }

   如果mOnScrollListener不为空的话，就调用mOnScrollListener的onScroll方法。而onScroll方法正是OnScrollListener接口定义的抽象方法，因为我们在ListView中继承了OnScrollListener接口，重载了onScroll方法，所以将会调用我们自己实现的onScroll方法。就是这样一个流程。

  然后看一下onScroll方法的实现，

@Override
     public void onScroll(AbsListView view, int firstVisibleItem,
               int visibleItemCount, int totalItemCount) {
          Log.i("onScroll", "onScroll");
          if (null != mPositionChangedListener && null != mScrollBarPanel) {

               // Don't do anything if there is no itemviews
               if (totalItemCount > 0) {
                    /*
                    * from android source code (ScrollBarDrawable.java)
                    */
                    final int thickness = getVerticalScrollbarWidth();
                    int height = Math.round((float) getMeasuredHeight()
                              * computeVerticalScrollExtent()
                              / computeVerticalScrollRange());
                    int thumbOffset = Math
                              .round((float) (getMeasuredHeight() - height)
                                        * computeVerticalScrollOffset()
                                        / (computeVerticalScrollRange() - computeVerticalScrollExtent()));
                    final int minLength = thickness * 2;
                    if (height < minLength) {
                         height = minLength;
                    }
                    thumbOffset += height / 2;

                    /*
                    * find out which itemviews the center of thumb is on
                    */
                    final int count = getChildCount();
                    for (int i = 0; i < count; ++i) {
                         final View childView = getChildAt(i);
                         if (childView != null) {
                              if (thumbOffset > childView.getTop()
                                        && thumbOffset < childView.getBottom()) {
                                   /*
                                   * we have our candidate
                                   */
                                   if (mLastPosition != firstVisibleItem + i) {
                                        mLastPosition = firstVisibleItem + i;

                                        /*
                                        * inform the position of the panel has changed
                                        */
                                        mPositionChangedListener.onPositionChanged(
                                                  this, mLastPosition, mScrollBarPanel);

                                        /*
                                        * measure panel right now since it has just
                                        * changed
                                        * 
                                        * INFO: quick hack to handle TextView has
                                        * ScrollBarPanel (to wrap text in case
                                        * TextView's content has changed)
                                        */
                                        measureChild(mScrollBarPanel,
                                                  mWidthMeasureSpec, mHeightMeasureSpec);
                                   }
                                   break;
                              }
                         }
                    }

                    /*
                    * update panel position
                    */
                    mScrollBarPanelPosition = thumbOffset
                              - mScrollBarPanel.getMeasuredHeight() / 2;
                    final int x = getMeasuredWidth()
                              - mScrollBarPanel.getMeasuredWidth()
                              - getVerticalScrollbarWidth();
                    mScrollBarPanel.layout(
                              x,
                              mScrollBarPanelPosition,
                              x + mScrollBarPanel.getMeasuredWidth(),
                              mScrollBarPanelPosition
                                        + mScrollBarPanel.getMeasuredHeight());
               }
          }

          if (mOnScrollListener != null) {
               mOnScrollListener.onScroll(view, firstVisibleItem,
                         visibleItemCount, totalItemCount);
          }
     }

  上面已经说到，这个onScroll是随着滑动而一直调用的，而我们的需求就是在滑动的时候弹出一个View来，所以这个方法正是处理问题的关键位置。可以在这里绘制弹出View的视图，从上面的代码也可以看出，就是在这里进行弹出View大小的计算以及位置的设定等。

   最后就是之前说的自定义ViewGroup的问题了，重载onMeasure()、onLayout()、ondispatchDraw()方法了，这个在本例中也是有所体现的，不过都比较简单，相信都看得懂。但是这几个方法都是在View初始化的时候调用的，而且只是调用一次，这样并不适合动态的绘制视图。所以这也是为什么本例子继承了OnScrollListener，然后在其onScroll方法中去绘制视图，因为onScroll方法在滑动的时候会调用，所以在滑动的时候就会绘制视图了。因此也可以看出本例采用的是动态绘图的方式，不是显示隐藏的方式。