一个强大的下拉刷新框架android-Ultra-Pull-To-Refresh

最新推荐文章于 2019-08-16 11:04:26 发布

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最新推荐文章于 2019-08-16 11:04:26 发布

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转http://blog.youkuaiyun.com/bboyfeiyu/article/details/45869393

最近在学习github上的一个开源项目：android-Ultra-Pull-To-Refresh(下面简称UltraPtr) 。这个项目主要用于Android APP中下拉刷新的功能。

OK，之所以说UltraPtr非常强大，是因为它有以下两个特点：
1. content可以是任意的view；
2. 简介完善的header抽象，用户可以对header高度自定义；

在理解了UltraPtr源码之后，我仿照它写了一个简单的下拉刷新应用。为了直观，先贴上效果图，然后再分析代码。

可以看到，UltraPtr框架支持各种content的下拉刷新，并且你也可以对头部header进行自定义，使用各种酷炫的header。

抽象接口

首先抽象出两个接口：PtrHandler和PtrUIHandler；

public interface PtrHandler
{
    /**
     * check can do refresh or not
     *
     * @param frame
     * @param content
     * @param header
     * @return
     */
    public boolean checkCanDoRefresh(final PtrFrameLayout frame, final View content, final View header);

    /**
     * when refresh begin
     *
     * @param frame
     */
    public void onRefreshBegin(final PtrFrameLayout frame);
}
 
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PtrHandler代表下拉刷新的功能接口，包含下拉刷新的回调，以及判断是否可以下拉。

public interface PtrUIHandler
{
    public void onUIReset(PtrFrameLayout frame);

    public void onUIRefreshPrepare(PtrFrameLayout frame);

    public void onUIRefreshBegin(PtrFrameLayout frame);

    public void onUIRefreshComplete(PtrFrameLayout frame);

    public void onUIPositionChange(PtrFrameLayout frame, boolean isUnderTouch, byte status, PtrIndicator ptrIndicator);
}
 
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PtrUIHandler是下拉刷新的UI接口，包括：准备下拉，下拉中，开始刷新，刷新完成，以及下拉过程中位置变化等回调方法。一般header需要实现此接口。

自定义下拉刷新控件PtrFrameLayout

测量与布局

PtrFrameLayout代表一个下拉刷新的自定义控件，继承自ViewGroup。有且只有两个子view：头部header和内容content。下面对类PtrFrameLayout中的主要方法进行分析。

和所有自定义控件一样，PtrFrameLayout通过重写onFinishInflate，onMeasure, onLayout来确定控件的大小和位置。

public class PtrFrameLayout extends ViewGroup
{
    //status enum
    public final static byte PTR_STATUS_INIT = 1;
    public byte mStatus = PTR_STATUS_INIT;
    public final static byte PTR_STATUS_PREPARE = 2;
    public final static byte PTR_STATUS_LOADING = 3;
    public final static byte PTR_STATUS_COMPLETE = 4;

    private PtrIndicator mPtrIndicator;

    private int mDurationToClose = 200;
    private int mDurationToCloseHeader = 1000;

    private long mLoadingStartTime = 0;

    private View mHeaderView;
    private View mContentView;

    private int mPagingTouchSlop;

    private final boolean DEBUG = true;
    private static int ID = 1;
    protected final String TAG = "ptr-frame-" + ++ID;

    private int mHeaderHeight;

    private boolean mPreventForHorizontal = false;

    private ScrollChecker mScrollChecker;

    private PtrHandler mPtrHandler;
    private PtrUIHandler mPtrUIHandler;

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

    public PtrFrameLayout(Context context, AttributeSet attrs)
    {
        this(context, attrs, 0);
    }

    public PtrFrameLayout(Context context, AttributeSet attrs, int defStyleAttr)
    {
        super(context, attrs, defStyleAttr);

        mPtrIndicator = new PtrIndicator();

        TypedArray a = context.obtainStyledAttributes(attrs, R.styleable.PtrFrameLayout, 0, 0);

        mDurationToClose = a.getInt(R.styleable.PtrFrameLayout_ptr_duration_to_close, mDurationToClose);
        mDurationToCloseHeader = a.getInt(R.styleable.PtrFrameLayout_ptr_duration_to_close_header, mDurationToCloseHeader);

        float resistence = a.getFloat(R.styleable.PtrFrameLayout_ptr_resistence, mPtrIndicator.getResistence());
        mPtrIndicator.setResistence(resistence);

        float ratio = a.getFloat(R.styleable.PtrFrameLayout_ptr_ratio_of_header_height_to_refresh, //
                mPtrIndicator.getRatioOfHeaderHeightToRefresh());
        mPtrIndicator.setRatioOfHeaderHeightToRefresh(ratio);

        a.recycle();

        mScrollChecker = new ScrollChecker();

        ViewConfiguration vc = ViewConfiguration.get(getContext());
        mPagingTouchSlop = vc.getScaledTouchSlop() * 2;
    }

    @Override
    protected void onFinishInflate()
    {
        int childCount = getChildCount();
        if (childCount > 2) {
            throw new IllegalStateException("PtrFrameLayout only can host 2 elements");
        } else if (childCount == 2) {
            mHeaderView = getChildAt(0);
            mContentView = getChildAt(1);
        } else if (childCount == 1) {
            mContentView = getChildAt(0);
        } else {
            TextView errorView = new TextView(getContext());
            errorView.setClickable(true);
            errorView.setTextColor(0xffff6600);
            errorView.setGravity(Gravity.CENTER);
            errorView.setTextSize(20);
            errorView.setText("The content view in PtrFrameLayout is empty!");
            mContentView = errorView;
            addView(mContentView);
        }

        if (mHeaderView != null) {
            mHeaderView.bringToFront();
        }

        super.onFinishInflate();
    }

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

        if (DEBUG) {
            HLog.d(TAG, "onMeasure frame: width: %s, height: %s, padding: %s %s %s %s", getMeasuredWidth(), //
                    getMeasuredHeight(), getPaddingLeft(), getPaddingTop(), getPaddingRight(), getPaddingBottom());
        }

        //测量子view
        if (mHeaderView != null) {
            measureChildWithMargins(mHeaderView, widthMeasureSpec, 0, heightMeasureSpec, 0);
            MarginLayoutParams lp = (MarginLayoutParams) mHeaderView.getLayoutParams();
            mHeaderHeight = mHeaderView.getMeasuredHeight() + lp.topMargin + lp.bottomMargin;
            mPtrIndicator.setHeaderHeight(mHeaderHeight);
        }
        if (mContentView != null) {
            measureContentView(mContentView, widthMeasureSpec, heightMeasureSpec);
        }
    }

    private void measureContentView(View child, int parentWidthMeasureSpec, int parentHeightMeasureSpec)
    {
        MarginLayoutParams lp = (MarginLayoutParams) child.getLayoutParams();
        int widthMeasureSpec = getChildMeasureSpec(parentWidthMeasureSpec, //
                getPaddingLeft() + getPaddingRight() + lp.leftMargin + lp.rightMargin, lp.width);
        int heightMeasureSpec = getChildMeasureSpec(parentHeightMeasureSpec, //
                getPaddingTop() + getPaddingBottom() + lp.topMargin + lp.bottomMargin, lp.height);

        child.measure(widthMeasureSpec, heightMeasureSpec);
    }

    @Override
    protected void onLayout(boolean changed, int l, int t, int r, int b)
    {
        int offsetY = mPtrIndicator.getCurrentPosY();
        int paddingLeft = getPaddingLeft();
        int paddingTop = getPaddingTop();

        if (mHeaderView != null) {
            MarginLayoutParams lp = (MarginLayoutParams) mHeaderView.getLayoutParams();
            final int left = paddingLeft + lp.leftMargin;
            final int top = paddingTop + lp.topMargin - mHeaderHeight + offsetY;
            final int right = left + mHeaderView.getMeasuredWidth();
            final int bottom = top + mHeaderView.getMeasuredHeight();
            mHeaderView.layout(left, top, right, bottom);
            if (DEBUG) {
                HLog.d(TAG, "onLayout header: %s %s %s %s", left, top, right, bottom);
            }
        }

        if (mContentView != null) {
            MarginLayoutParams lp = (MarginLayoutParams) mContentView.getLayoutParams();
            final int left = paddingLeft + lp.leftMargin;
            final int top = paddingTop + lp.topMargin + offsetY;
            final int right = left + mContentView.getMeasuredWidth();
            final int bottom = top + mContentView.getMeasuredHeight();
            mContentView.layout(left, top, right, bottom);
            if (DEBUG) {
                HLog.d(TAG, "onLayout content: %s %s %s %s", left, top, right, bottom);
            }
        }
    }

    @Override
    protected LayoutParams generateDefaultLayoutParams()
    {
        return new MarginLayoutParams(LayoutParams.MATCH_PARENT, LayoutParams.MATCH_PARENT);
    }

    @Override
    protected LayoutParams generateLayoutParams(LayoutParams p)
    {
        return new MarginLayoutParams(p);
    }

    @Override
    public LayoutParams generateLayoutParams(AttributeSet attrs)
    {
        return new MarginLayoutParams(getContext(), attrs);
    }
    ......
    ......
    ......
}
 
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首先，我们在构造函数PtrFrameLayout(Context context, AttributeSet attrs, int defStyleAttr)获取自定义属性值，以及初始化一些成员变量，其中mScrollChecker是一个runnable对象，主要用来实现View的平滑移动，下面会有详细解释。

在onFinishInflate()回调方法中，根据布局文件中子view的个数对成员变量mHeaderView和mContentView进行初始化。外部可以同时在布局文件中指定mHeaderView和mContentView，也可以只指定mContentView，mHeaderView通过代码进行设置。

在onMeasure()回调方法中，对子view进行了测量。首先使用measureChildWithMargins()对头部mHeaderView进行了测量，之后将头部的测量的高度更新到PtrIndicator变量中，PtrIndicator是一个工具类，主要负责跟踪记录滑动过程中Y方向的偏移量等等。

在onLayout()回调方法中，通过top = paddingTop + lp.topMargin - mHeaderHeight + offsetY; 计算出header的top值，可以看到header向上偏移了mHeaderHeight，这样头部header初始情况下就会被隐藏。注意，代码中有个offsetY，初始值为0，随着下拉过程中，offsetY会逐渐增大，这样header和content都会向下移动，header就会显示出来，出现下拉位置移动的效果。

计算子view大小的时候用到了MarginLayoutParams，所以我们需要重写generateDefaultLayoutParams()方法。

事件处理

ViewGroup的事件处理，通常重写onInterceptTouchEvent 方法或者 dispatchTouchEvent 方法，PtrFrameLayout重写了dispatchTouchEvent 方法。

事件处理流程图如下：

后面我会附上源码，感兴趣的朋友可以对比源码去理解事件处理流程。

经典下拉刷新的头部

PtrClassicDefaultHeader.Java

private void resetView()
{
    mProgressBar.setVisibility(INVISIBLE);
    hideRotateView();
}

private void hideRotateView()
{
    mRotateView.clearAnimation();
    mRotateView.setVisibility(INVISIBLE);
}

@Override
public void onUIReset(PtrFrameLayout frame)
{
    resetView();

    mShoulShowLastUpdate = false;
    tryUpdateLastUpdateTime();
}
 
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重置header view，隐藏进度条，隐藏箭头，更新最后刷新事件

@Override
public void onUIRefreshPrepare(PtrFrameLayout frame)
{
    mShoulShowLastUpdate = true;
    tryUpdateLastUpdateTime();
    mLastUpdateTimeUpdater.start();

    mProgressBar.setVisibility(INVISIBLE);
    mRotateView.setVisibility(VISIBLE);
    mTitleView.setText(R.string.hebut_ptr_pull_down);
}
 
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准备刷新，隐藏进度条，显示旋转箭头，提示文字为：pull down；启动一个runnable对象，来实时更新上次刷新时间。

@Override
public void onUIRefreshBegin(PtrFrameLayout frame)
{
    hideRotateView();
    mProgressBar.setVisibility(VISIBLE);
    mTitleView.setVisibility(VISIBLE);
    mTitleView.setText(R.string.hebut_ptr_updating);

    mShoulShowLastUpdate = false;
    tryUpdateLastUpdateTime();
    mLastUpdateTimeUpdater.stop();
}
 
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开始刷新，隐藏旋转箭头，显示进度条，提示文字：updating。停止mLastUpdateTimeUpdater。

@Override
public void onUIRefreshComplete(PtrFrameLayout frame)
{
    hideRotateView();
    mProgressBar.setVisibility(INVISIBLE);
    mTitleView.setVisibility(VISIBLE);
    mTitleView.setText(R.string.hebut_ptr_update_complete);

    //update last update time
    SharedPreferences sharedPreferences = getContext().getSharedPreferences(KEY_SharedPreferences, 0);
    if(!TextUtils.isEmpty(mLastUpdateTimeKey)) {
        mLastUpdateTime = new Date().getTime();
        sharedPreferences.edit().putLong(mLastUpdateTimeKey, mLastUpdateTime).commit();
    }
}
 
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刷新完成，隐藏进度条，隐藏旋转箭头，提示文字：updated；向shared文件中更新最新刷新时间。

@Override
public void onUIPositionChange(PtrFrameLayout frame, boolean isUnderTouch, byte status, PtrIndicator ptrIndicator)
{
    final int offsetToRefresh = ptrIndicator.getOffsetToRefresh();
    final int currentPos = ptrIndicator.getCurrentPosY();
    final int lastPos = ptrIndicator.getLastPos();

    if(currentPos < offsetToRefresh && lastPos >= offsetToRefresh) {
        if(isUnderTouch && status == frame.PTR_STATUS_PREPARE) {
            crossRotateLineFromBottomUnderTouch();
        }
    } else if(currentPos > offsetToRefresh && lastPos <= offsetToRefresh) {
        if(isUnderTouch && status == frame.PTR_STATUS_PREPARE) {
            crossRotateLineFromTopUnderTouch();
        }
    }
}
 
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