Android 滑动效果高级篇（八）—— 自定义控件

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自定义控件，较常用View、ViewGroup、Scroller三个类，其继承关系如下：

本示例自定义控件，实现一个Gallery效果，并添加了一个显示View个数和位置的bar条，效果图：

自定义控件，包含通过继承实现的自定义控件和自定义控件属性两部分，即控件和属性

1、自定义属性

自定义属性，分为定义属性、解析属性、设置属性三部分，具体步骤：

首先，在res/valus/attrs.xml属性资源文件中，定义控件属性

xml version="1.0" encoding="utf-8"?>
<resources>
    <declare-styleable name="com.myapps.widget.Pager">
        <attr name="pageWidth" format="dimension" />
    declare-styleable>

    <declare-styleable name="com.myapps.widget.PagerBar">
        <attr name="barColor" format="color" />
        <attr name="highlightColor" format="color" />
        <attr name="fadeDelay" format="integer" />
        <attr name="fadeDuration" format="integer" />
        <attr name="roundRectRadius" format="dimension" />
    declare-styleable>
resources>

然后，在自定义控件的代码中，解析自定义的属性，如在PagerBar.java：

// 自定义属性
        TypedArray a = context.obtainStyledAttributes(attrs, R.styleable.com_myapps_widget_PagerBar);
        int barBackColor = a.getColor(R.styleable.com_myapps_widget_PagerBar_barColor, DEFAULT_BAR_BACKCOLOR);              // bar背景色
        int barForeColor = a.getColor(R.styleable.com_myapps_widget_PagerBar_highlightColor, DEFAULT_BAR_FORECOLOR);    // bar前景色
        fadeDelay = a.getInteger(R.styleable.com_myapps_widget_PagerBar_fadeDelay, DEFAULT_FADE_DELAY);             // bar消失延迟时间
        fadeDuration = a.getInteger(R.styleable.com_myapps_widget_PagerBar_fadeDuration, DEFAULT_FADE_DURATION);    // bar消失动画时间
        ovalRadius = a.getDimension(R.styleable.com_myapps_widget_PagerBar_roundRectRadius, 2f);
        a.recycle();

最后，在布局文件中设置属性，如在main.xml

<com.homer.mycontrol.PagerBar
    android:id="@+id/control"
    android:layout_width="fill_parent"
    android:layout_height="4dip"
    android:layout_margin="8dip"
    myapps:roundRectRadius="2dip" />

其中，在布局中间main.xml中，需要注意：

xmlns:myapps="http://schemas.android.com/apk/res/com.homer.mycontrol"

定义属性时，在declare-styleable的name中，需要包含com.myapps.widget.PagerBar，表示自定义的控件PageBar是widget子类，myapps是xmlns解析标记

解析属性时，在TypedArray中，需要包含R.styleable.com_myapps_widget_PagerBar，横线替换了圆点.

定义属性时，在com.homer.mycontrol.PagerBar中，需要包含myapps:roundRectRadius="2dip"，加上myapps解析标记

2、自定义控件PagerBar

自定义PagerBar，在图片下方用来显示图片滑到了第几页，即上面效果图（图2、图3）中的下部银白色细条，具体实现：

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

    // 自定义属性
    TypedArray a = context.obtainStyledAttributes(attrs, R.styleable.com_myapps_widget_PagerBar);
    int barBackColor = a.getColor(R.styleable.com_myapps_widget_PagerBar_barColor, DEFAULT_BAR_BACKCOLOR);              // bar背景色
    int barForeColor = a.getColor(R.styleable.com_myapps_widget_PagerBar_highlightColor, DEFAULT_BAR_FORECOLOR);    // bar前景色
    fadeDelay = a.getInteger(R.styleable.com_myapps_widget_PagerBar_fadeDelay, DEFAULT_FADE_DELAY);             // bar消失延迟时间
    fadeDuration = a.getInteger(R.styleable.com_myapps_widget_PagerBar_fadeDuration, DEFAULT_FADE_DURATION);    // bar消失动画时间
    ovalRadius = a.getDimension(R.styleable.com_myapps_widget_PagerBar_roundRectRadius, 2f);
    a.recycle();

    barBackPaint = new Paint();
    barBackPaint.setColor(barBackColor);

    barForePaint = new Paint();
    barForePaint.setColor(barForeColor);

    fadeOutAnimation = new AlphaAnimation(1f, 0f);
    fadeOutAnimation.setDuration(fadeDuration);
    fadeOutAnimation.setRepeatCount(0);
    fadeOutAnimation.setInterpolator(new LinearInterpolator());
    fadeOutAnimation.setFillEnabled(true);
    fadeOutAnimation.setFillAfter(true);
}

public int getNumPages() {
    return numPages;
}

public void setNumPages(int numPages) {
    if (numPages <= 0) {
        throw new IllegalArgumentException("numPages must be positive");
    }
    this.numPages = numPages;
    invalidate();       // 重绘View
    fadeOut();          // 设置bar消失效果
}

/** bar消失动画 */
private void fadeOut() {
    if (fadeDuration > 0) {
        clearAnimation();
        fadeOutAnimation.setStartTime(AnimationUtils.currentAnimationTimeMillis() + fadeDelay); //延迟fadeDelay后动画开始
        setAnimation(fadeOutAnimation);
    }
}

/**  @return  0 to numPages-1 */
public int getCurrentPage() {
    return currentPage;
}

/** @param currentPage  0 to numPages-1  */
public void setCurrentPage(int currentPage) {
    if (currentPage < 0 || currentPage >= numPages) {
        throw new IllegalArgumentException("currentPage parameter out of bounds");
    }
    if (this.currentPage != currentPage) {
        this.currentPage = currentPage;
        this.position = currentPage * getPageWidth();   // bar前景色滑动条的起始位置（像素值）
        invalidate();
        fadeOut();
    }
}

/** 获取View的宽度，即bar的宽度 */
public int getPageWidth() {
    return getWidth() / numPages;   // getWidth()是PagerBar的宽度（减去了margin左右距离后）
}

/**  @param position     can be -pageWidth to pageWidth*(numPages+1)  */
public void setPosition(int position) {
    if (this.position != position) {
        this.position = position;
        invalidate();
        fadeOut();
    }
}

@Override
protected void onDraw(Canvas canvas) {
    canvas.drawRoundRect(new RectF(0, 0, getWidth(), getHeight()), ovalRadius, ovalRadius, barBackPaint);   // 绘制bar背景
    canvas.drawRoundRect(new RectF(position, 0, position + (getWidth() / numPages), getHeight()), ovalRadius, ovalRadius, barForePaint);    // 绘制bar前景
}

3、自定义控件Pager

自定义控件Pager，继承自ViewGroup，用来显示图片的，类似于Gallery，实现主要部分包含：

A、自定义属性解析

B、Pager容器控件Scroller滑动页设置与控制

C、容器状态保存（onSaveInstanceState）

D、容器事件监听接口

详细实现如下：

A、自定义属性解析

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

    // 自定义属性
    TypedArray a = context.obtainStyledAttributes(attrs, R.styleable.com_myapps_widget_Pager);
    pageWidthSpec = a.getDimensionPixelSize(R.styleable.com_myapps_widget_Pager_pageWidth, SPEC_UNDEFINED);
    a.recycle();
}

B、Pager容器控件Scroller滑动页设置与控制

public void setCurrentPage(int currentPage) {
    mCurrentPage = Math.max(0, Math.min(currentPage, getChildCount()));     // 非常好
    scrollTo(getScrollXForPage(mCurrentPage), 0);
    invalidate();   // 重绘View
}

int getCurrentPage() {
    return mCurrentPage;
}

public void setPageWidth(int pageWidth) {
    this.pageWidthSpec = pageWidth;
}

public int getPageWidth() {
    return pageWidth;
}

/** 获取whichPage的Pager起始x位置，whichPage从0开始计 */
private int getScrollXForPage(int whichPage) {
    return (whichPage * pageWidth) - pageWidthPadding();
}

/** 返回View的 paddingwidth 一半(1/2)*/
int pageWidthPadding() {
    return ((getMeasuredWidth() - pageWidth) / 2);
}

@Override
public void computeScroll() {       // update  mScrollX and mScrollY  of View
    if (mScroller.computeScrollOffset()) {
        scrollTo(mScroller.getCurrX(), mScroller.getCurrY());
        postInvalidate();           // invalidate the View from a non-UI thread
    } else if (mNextPage != INVALID_SCREEN) {
        mCurrentPage = mNextPage;
        mNextPage = INVALID_SCREEN;
        clearChildrenCache();
    }
}

@Override
protected void dispatchDraw(Canvas canvas) {    // draw the child views

    final long drawingTime = getDrawingTime();  // 绘制childView
    final int count = getChildCount();
    for (int i = 0; i < count; i++) {
        drawChild(canvas, getChildAt(i), drawingTime);
    }

    for (OnScrollListener mListener : mListeners) { // 自定义接口
        int adjustedScrollX = getScrollX() + pageWidthPadding();
        mListener.onScroll(adjustedScrollX);
        if (adjustedScrollX % pageWidth == 0) { // scroll finished
            mListener.onViewScrollFinished(adjustedScrollX / pageWidth);
        }
    }
}

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

    pageWidth = (pageWidthSpec == SPEC_UNDEFINED) ? getMeasuredWidth() : pageWidthSpec;
    pageWidth = Math.min(pageWidth, getMeasuredWidth());

    final int count = getChildCount();
    for (int i = 0; i < count; i++) {
        widthMeasureSpec = MeasureSpec.makeMeasureSpec(pageWidth, MeasureSpec.EXACTLY);
        getChildAt(i).measure(widthMeasureSpec, heightMeasureSpec);
    }

    if (mFirstLayout) { // 第一次显示Pager时，page的位置
        scrollTo(getScrollXForPage(mCurrentPage), mScroller.getCurrY());
        mFirstLayout = false;
    }
}

@Override
protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
    int childLeft = 0;

    final int count = getChildCount();  // 绘制childView
    for (int i = 0; i < count; i++) {
        final View child = getChildAt(i);
        if (child.getVisibility() != View.GONE) {
            final int childWidth = child.getMeasuredWidth();
            child.layout(childLeft, 0, childLeft + childWidth, child.getMeasuredHeight());
            childLeft += childWidth;
        }
    }
}

@Override
public boolean onInterceptTouchEvent(MotionEvent ev) {
    final int action = ev.getAction();
    if ((action == MotionEvent.ACTION_MOVE) && (mTouchState != TOUCH_STATE_REST)) { // 正在滑动中
        return true;
    }

    final float x = ev.getX();
    final float y = ev.getY();

    switch (action) {
    case MotionEvent.ACTION_MOVE:
        if (mTouchState == TOUCH_STATE_REST) {
            checkStartScroll(x, y);
        }
        break;

    case MotionEvent.ACTION_DOWN:
        mLastMotionX = x;
        mLastMotionY = y;
        mAllowLongPress = true;

        mTouchState = mScroller.isFinished() ? TOUCH_STATE_REST : TOUCH_STATE_SCROLLING;    // scroll 完成后，重置状态
        break;

    case MotionEvent.ACTION_CANCEL:
    case MotionEvent.ACTION_UP:
        clearChildrenCache();
        mTouchState = TOUCH_STATE_REST;
        break;
    }

    return mTouchState != TOUCH_STATE_REST;
}

@Override
public boolean onTouchEvent(MotionEvent ev) {
    if (mVelocityTracker == null) {
        mVelocityTracker = VelocityTracker.obtain();
    }
    mVelocityTracker.addMovement(ev);

    final int action = ev.getAction();
    final float x = ev.getX();
    final float y = ev.getY();

    switch (action) {
    case MotionEvent.ACTION_DOWN:
        if (!mScroller.isFinished()) {
            mScroller.abortAnimation();
        }
        mLastMotionX = x;
        break;

    case MotionEvent.ACTION_MOVE:
        if (mTouchState == TOUCH_STATE_REST) {
            checkStartScroll(x, y);
        } else if (mTouchState == TOUCH_STATE_SCROLLING) {  // scrolling 状态时，重绘view
            int deltaX = (int) (mLastMotionX - x);
            mLastMotionX = x;

            if (getScrollX() < 0 || getScrollX() > getChildAt(getChildCount() - 1).getLeft()) {
                deltaX /= 2;
            }
            scrollBy(deltaX, 0);
        }
        break;

    case MotionEvent.ACTION_UP:
        if (mTouchState == TOUCH_STATE_SCROLLING) {
            final VelocityTracker velocityTracker = mVelocityTracker;
            velocityTracker.computeCurrentVelocity(1000, mMaximumVelocity);
            int velocityX = (int) velocityTracker.getXVelocity();

            if (velocityX > SNAP_VELOCITY && mCurrentPage > 0) {
                snapToPage(mCurrentPage - 1);
            } else if (velocityX < -SNAP_VELOCITY && mCurrentPage < getChildCount() - 1) {
                snapToPage(mCurrentPage + 1);
            } else {
                snapToDestination();
            }

            if (mVelocityTracker != null) {
                mVelocityTracker.recycle();
                mVelocityTracker = null;
            }
        }
        mTouchState = TOUCH_STATE_REST;
        break;
    case MotionEvent.ACTION_CANCEL:
        mTouchState = TOUCH_STATE_REST;
    }

    return true;
}

/** 检查scroll状态，并设置绘制scroll缓存 */
private void checkStartScroll(float x, float y) {
    final int xDiff = (int) Math.abs(x - mLastMotionX);
    final int yDiff = (int) Math.abs(y - mLastMotionY);

    boolean xMoved = xDiff > mTouchSlop;
    boolean yMoved = yDiff > mTouchSlop;

    if (xMoved || yMoved) {
        if (xMoved) {
            mTouchState = TOUCH_STATE_SCROLLING;        // 设置为scrolling 状态
            enableChildrenCache();
        }
        if (mAllowLongPress) {
            mAllowLongPress = false;
            final View currentScreen = getChildAt(mCurrentPage);
            currentScreen.cancelLongPress();    // Cancels a pending long press
        }
    }
}

void enableChildrenCache() {
    setChildrenDrawingCacheEnabled(true);       // Enables or disables the drawing cache for each child of this viewGroup
    setChildrenDrawnWithCacheEnabled(true); // Tells the ViewGroup to draw its children using their drawing cache
}

void clearChildrenCache() {
    setChildrenDrawnWithCacheEnabled(false);
}

private void snapToDestination() {
    final int startX = getScrollXForPage(mCurrentPage);
    int whichPage = mCurrentPage;
    if (getScrollX() < startX - getWidth() / 8) {
        whichPage = Math.max(0, whichPage - 1);
    } else if (getScrollX() > startX + getWidth() / 8) {
        whichPage = Math.min(getChildCount() - 1, whichPage + 1);
    }

    snapToPage(whichPage);
}

void snapToPage(int whichPage) {
    enableChildrenCache();

    boolean changingPages = whichPage != mCurrentPage;

    mNextPage = whichPage;

    View focusedChild = getFocusedChild();
    if (focusedChild != null && changingPages && focusedChild == getChildAt(mCurrentPage)) {
        focusedChild.clearFocus();
    }

    final int newX = getScrollXForPage(whichPage);
    final int delta = newX - getScrollX();
    mScroller.startScroll(getScrollX(), 0, delta, 0, Math.abs(delta) * 2);
    invalidate();
}

/** 向左滑动 */
public void scrollLeft() {
    if (mNextPage == INVALID_SCREEN && mCurrentPage > 0 && mScroller.isFinished()) {
        snapToPage(mCurrentPage - 1);
    }
}

/** 向右滑动 */
public void scrollRight() {
    if (mNextPage == INVALID_SCREEN && mCurrentPage < getChildCount() - 1 && mScroller.isFinished()) {
        snapToPage(mCurrentPage + 1);
    }
}

C、容器状态保存（onSaveInstanceState）

/** 保存状态 */
public static class SavedState extends BaseSavedState {
    int currentScreen = -1;

    SavedState(Parcelable superState) {
        super(superState);
    }

    private SavedState(Parcel in) {
        super(in);
        currentScreen = in.readInt();
    }

    public static final Parcelable.Creator CREATOR = new Parcelable.Creator() {
        public SavedState createFromParcel(Parcel in) { // get data written by Parcelable.writeToParcel()
            return new SavedState(in);
        }

        public SavedState[] newArray(int size) {            // create  array of the Parcelable
            return new SavedState[size];
        }
    };

    @Override
    public void writeToParcel(Parcel out, int flags) {      // set data to parcel
        super.writeToParcel(out, flags);
        out.writeInt(currentScreen);
    }

}

@Override
protected Parcelable onSaveInstanceState() {        // 保存状态
    final SavedState state = new SavedState(super.onSaveInstanceState());
    state.currentScreen = mCurrentPage;     // save InstanceState
    return state;
}

@Override
protected void onRestoreInstanceState(Parcelable state) {   // 恢复状态
    SavedState savedState = (SavedState) state;
    super.onRestoreInstanceState(savedState.getSuperState());   // get InstanceState
    if (savedState.currentScreen != INVALID_SCREEN) {
        mCurrentPage = savedState.currentScreen;
    }
}

D、容器事件监听接口

public void addOnScrollListener(OnScrollListener listener) {
    mListeners.add(listener);
}

public void removeOnScrollListener(OnScrollListener listener) {
    mListeners.remove(listener);
}

/** 自定义接口 */
public static interface OnScrollListener {
    void onScroll(int scrollX);
    void onViewScrollFinished(int currentPage);
}

代码下载

参考推荐：

Android中自定义属性的使用

Android中自定义属性的格式详解

Scroller（Android）  Scroller（cnblog）

Android Parcelable

Android左右滑动加载分页