（一） 两个接口（IPullToRefresh、ILoadingLayout）与一个基类（PullToRefreshBase）

     本文主要介绍PullToRefresh框架中的两个接口和一个基类，这些是下拉刷新框架的基础和核心；

一、IPullToRefresh接口：

      IPullToRefresh主要定义了View下拉刷新过程中需要实现的一些基本方法；这些方法主要用来控制列表的一些状态；这些方法包括，下面主要介绍一下这个接口中的核心方法；

      用我渣渣的英语水平大概翻译了几个核心方法，大牛直接无视吧........

public interface IPullToRefresh<T extends View> {
    T：泛型用法，用来表示要能引用刷新的View，比如：ListView、Gridiew、ScrollView等；
    /**
     *
     * 当前的Mode为Mode.BOTH的时候，通过这个方法可以获取view的真实状态；
     *
     * Get the mode that this view is currently in. This is only really useful
     * when using <code>Mode.BOTH</code>.
     *
     * @return Mode that the view is currently in
     */
    public Mode getCurrentMode();

    /**
     *
     * Returns whether the Touch Events are filtered or not. If true is
     * returned, then the View will only use touch events where the difference
     * in the Y-axis is greater than the difference in the X-axis. This means
     * that the View will not interfere when it is used in a horizontal
     * scrolling View (such as a ViewPager).
     *
     * @return boolean - true if the View is filtering Touch Events
     */
    public boolean getFilterTouchEvents();

    /**
     * Returns a proxy object which allows you to call methods on all of the
     * LoadingLayouts (the Views which show when Pulling/Refreshing).
     * <p />
     * You should not keep the result of this method any longer than you need
     * it.
     * 代理模式的应用；返回下拉、上拉布局的代理对象，用来控制相应上拉、下拉布局的显示状态；
     * @return Object which will proxy any calls you make on it, to all of the
     *         LoadingLayouts.
     */
    public ILoadingLayout getLoadingLayoutProxy();

    /**
     * Returns a proxy object which allows you to call methods on the
     * LoadingLayouts (the Views which show when Pulling/Refreshing). The actual
     * LoadingLayout(s) which will be affected, are chosen by the parameters you
     * give.
     * <p />
     * You should not keep the result of this method any longer than you need
     * it.
     * 代理模式的应用；返回下拉、上拉布局的代理对象；
     * 通过设置参数，可以影响这些布局的显示状态；
     *
     * @param includeStart - Whether to include the Start/Header Views
     * @param includeEnd - Whether to include the End/Footer Views
     * @return Object which will proxy any calls you make on it, to the
     *         LoadingLayouts included.
     */
    public ILoadingLayout getLoadingLayoutProxy(boolean includeStart, boolean includeEnd);

    /**
     * Get the mode that this view has been set to. If this returns
     * <code>Mode.BOTH</code>, you can use <code>getCurrentMode()</code> to
     * check which mode the view is currently in
     * 返回当前View当前所处的状态，如果这个方法返回为Mode.BOTH，你可以通过getCurrentMode()方法
     * 进一步检查当前View所处的状态
     *
     * @return Mode that the view has been set to
     */
    public Mode getMode();

    /**
     * Get the Wrapped Refreshable View. Anything returned here has already been
     * added to the content view.
     *
     * 获取包装好的Refreshable View，无论当前返回的是什么View，该View都已经被添加到了
     * LinearLayout中（后面看代码会明白）
     *
     * @return The View which is currently wrapped
     */
    public T getRefreshableView();

    /**
     * Get whether the 'Refreshing' View should be automatically shown when
     * refreshing. Returns true by default.
     *
     * 返回一个布尔值来表示正在刷新的View在刷新时是否正在被展示，默认返回true；
     *
     * @return - true if the Refreshing View will be show
     */
    public boolean getShowViewWhileRefreshing();

    /**
     * @return - The state that the View is currently in.
     *
     * 返回View的当前State（enum，后续会讲到）
     *
     */
    public State getState();

    /**
     * Whether Pull-to-Refresh is enabled
     *
     * 返回一个布尔值来表示pull-to-refresh动作是否结束；
     *
     * @return enabled
     */
    public boolean isPullToRefreshEnabled();

    /**
     * Gets whether Overscroll support is enabled. This is different to
     * Android's standard Overscroll support (the edge-glow) which is available
     * from GINGERBREAD onwards
     *
     *
     *
     * @return true - if both PullToRefresh-OverScroll and Android's inbuilt
     *         OverScroll are enabled
     */
    public boolean isPullToRefreshOverScrollEnabled();

    /**
     * Returns whether the Widget is currently in the Refreshing mState
     *
     * 返回一个布尔值来表示正在刷新的状态是否结束；
     *
     * @return true if the Widget is currently refreshing
     */
    public boolean isRefreshing();

    /**
     * Returns whether the widget has enabled scrolling on the Refreshable View
     * while refreshing.
     *
     * @return true if the widget has enabled scrolling while refreshing
     */
    public boolean isScrollingWhileRefreshingEnabled();

    /**
     * Mark the current Refresh as complete. Will Reset the UI and hide the
     * Refreshing View
     *
     * 标记当前刷新完成，即将重置UI，隐藏正在刷新的view；
     *
     */
    public void onRefreshComplete();

    /**
     * Set the Touch Events to be filtered or not. If set to true, then the View
     * will only use touch events where the difference in the Y-axis is greater
     * than the difference in the X-axis. This means that the View will not
     * interfere when it is used in a horizontal scrolling View (such as a
     * ViewPager), but will restrict which types of finger scrolls will trigger
     * the View.
     *
     * @param filterEvents - true if you want to filter Touch Events. Default is
     *            true.
     */
    public void setFilterTouchEvents(boolean filterEvents);

    /**
     * Set the mode of Pull-to-Refresh that this view will use.
     *
     * 设置Pull-to-Refresh的mode
     *
     * @param mode - Mode to set the View to
     */
    public void setMode(Mode mode);

    /**
     * Set OnPullEventListener for the Widget
     *
     * @param listener - Listener to be used when the Widget has a pull event to
     *            propogate.
     */
    public void setOnPullEventListener(OnPullEventListener<T> listener);

    /**
     * Set OnRefreshListener for the Widget
     *
     * @param listener - Listener to be used when the Widget is set to Refresh
     */
    public void setOnRefreshListener(OnRefreshListener<T> listener);

    /**
     * Set OnRefreshListener for the Widget
     *
     * @param listener - Listener to be used when the Widget is set to Refresh
     */
    public void setOnRefreshListener(OnRefreshListener2<T> listener);

    /**
     * Sets whether Overscroll support is enabled. This is different to
     * Android's standard Overscroll support (the edge-glow). This setting only
     * takes effect when running on device with Android v2.3 or greater.
     *
     * 设置是否启用Overscroll support，这个不同于android标准的Overscroll support
     * 这个设置仅仅是当框架运行在2.3及更高版本才起作用；
     *
     * @param enabled - true if you want Overscroll enabled
     */
    public void setPullToRefreshOverScrollEnabled(boolean enabled);

    /**
     * Sets the Widget to be in the refresh state. The UI will be updated to
     * show the 'Refreshing' view, and be scrolled to show such.
     *
     * 设置控件正在刷新时的状态；这个时候将展示正在刷新的UI；
     *
     */
    public void setRefreshing();

    /**
     * Sets the Widget to be in the refresh state. The UI will be updated to
     * show the 'Refreshing' view.
     *
     * 通过参数来设置是否要显示正在刷新的UI；
     *
     * @param doScroll - true if you want to force a scroll to the Refreshing
     *            view.
     */
    public void setRefreshing(boolean doScroll);

    /**
     * Sets the Animation Interpolator that is used for animated scrolling.
     * Defaults to a DecelerateInterpolator
     *
     * @param interpolator - Interpolator to use
     */
    public void setScrollAnimationInterpolator(Interpolator interpolator);

    /**
     * By default the Widget disables scrolling on the Refreshable View while
     * refreshing. This method can change this behaviour.
     *
     * @param scrollingWhileRefreshingEnabled - true if you want to enable
     *            scrolling while refreshing
     */
    public void setScrollingWhileRefreshingEnabled(boolean scrollingWhileRefreshingEnabled);

    /**
     * A mutator to enable/disable whether the 'Refreshing' View should be
     * automatically shown when refreshing.
     *
     * @param showView
     */
    public void setShowViewWhileRefreshing(boolean showView);

}

二、ILoadingLayout接口：

      这个接口主要用于控制上拉、下拉显示的Layout的一些状态，包括一些需要更新的文案、视图等；

public interface ILoadingLayout {

    /**
     *
     * Set the Last Updated Text. This displayed under the main label when
     * Pulling
     *
     * 设置最新更新的文案；上拉、下拉view的时候显示在主标签上；
     *
     * @param label - Label to set
     */
    public void setLastUpdatedLabel(CharSequence label);

    /**
     *
     * Set the drawable used in the loading layout. This is the same as calling
     * <code>setLoadingDrawable(drawable, Mode.BOTH)</code>
     *
     * 设置正在加载时候的drawable；等价于调用setLoadingDrawable(drawable, Mode.BOTH)
     *
     * @param drawable - Drawable to display
     */
    public void setLoadingDrawable(Drawable drawable);

    /**
     *
     * Set Text to show when the Widget is being Pulled
     * <code>setPullLabel(releaseLabel, Mode.BOTH)</code>
     *
     * 设置正在被拉动时显示的文案；
     *
     * @param pullLabel - CharSequence to display
     */
    public void setPullLabel(CharSequence pullLabel);

    /**
     *
     * Set Text to show when the Widget is refreshing
     * <code>setRefreshingLabel(releaseLabel, Mode.BOTH)</code>
     *
     * 设置正在刷新时显示文案；
     *
     * @param refreshingLabel - CharSequence to display
     */
    public void setRefreshingLabel(CharSequence refreshingLabel);

    /**
     *
     * Set Text to show when the Widget is being pulled, and will refresh when
     * released. This is the same as calling
     * <code>setReleaseLabel(releaseLabel, Mode.BOTH)</code>
     *
     * 当上拉、下拉结束，松手时，设置文案；
     *
     * @param releaseLabel - CharSequence to display
     */
    public void setReleaseLabel(CharSequence releaseLabel);

    /**
     *
     * Set's the Sets the typeface and style in which the text should be
     * displayed.
     *
     * 设置文案展示时候typeface和style
     *
     * Please see
     * {@link android.widget.TextView#setTypeface(Typeface)
     * TextView#setTypeface(Typeface)}.
     */
    public void setTextTypeface(Typeface tf);
}

三、PullToRefreshBase抽象类：

       public abstract class PullToRefreshBase<T extends View> extends LinearLayout implements IPullToRefresh<T>

      这个类是一个抽象类，继承自LinearLayout，实现了IPullToRefresh接口；首先，它是对需要上拉、下拉View（比如：ListView、GridView等）的一个Wrapper，里面实现了对上拉、下拉View的初始化操作，并且监听了上拉、下拉期间一系列的操作事件，及回调方法，它是IPullToRefresh的直接实现，是框架的核心中的核心；这里只做简单介绍，后面的文章会分两个篇幅来介绍这个类；