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打造万能的BannerView(ViewPager)无限轮播图

96
Steven_520
2018.05.11 23:45* 字数 707

为什么写这篇文章,因为在网上看到的绝大多数BannerView实现了右无限轮播图,甚至没有实现无限轮播图,说成是无限轮播图,实现了左右无限轮播图的,并没有做性能上的优化。

先看张效果图

device-2018-05-11-173850.gif

工程目录图

project.png

BannerAdapter:banner轮播图的适配器,因为服务器返回的列表图片的url,显示的时候需要转成IamgeViw;  
BannerScroller:设置切换页面的持续时间;  
BannerView:继承RelativeLayout,包含BannViewPager和底部DotIndicatorView指示器;
BannerViewPager:继承ViewPager,设置ViewPager的适配器Adpter和动画;
DotIndicatorView:底部指示器;

DotIndicatorView类

public class DotIndicatorView extends View {
//形状
private int mShape;
// 矩形
public static final int SHAPE_REC = 1;
// 圆形
public static final int SHAPE_CIRCLE = 2;
private Drawable mDrawable;

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

public DotIndicatorView(Context context, @Nullable AttributeSet attrs) {
    this(context, attrs, 0);
}

public DotIndicatorView(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
    super(context, attrs, defStyleAttr);
    TypedArray typedArray = context.obtainStyledAttributes(attrs, R.styleable.DotIndicatorView);
    //默认是圆形
    mShape = typedArray.getInteger(R.styleable.DotIndicatorView_shape, SHAPE_CIRCLE);
    typedArray.recycle();

}

@Override
protected void onDraw(Canvas canvas) {
    super.onDraw(canvas);
    if (mDrawable != null) {
        Bitmap bitmap = drawableToBitmap(mDrawable);
        if (mShape == SHAPE_CIRCLE) {
            Bitmap circleBitmap = getCircleBitmap(bitmap);
            canvas.drawBitmap(circleBitmap, 0, 0, null);
        } else if (mShape == SHAPE_REC) {
            Bitmap recBitmap = getRecBitmap(bitmap);
            canvas.drawBitmap(recBitmap, 0, 0, null);
        }
    }
}

public void setDrawable(Drawable drawable) {
    mDrawable = drawable;
    invalidate();
}

/**
 * drawable转bitmap
 *
 * @param drawable
 * @return
 */
private Bitmap drawableToBitmap(Drawable drawable) {
    if (drawable instanceof BitmapDrawable) {
        return (( BitmapDrawable ) drawable).getBitmap();
    }
    //其他类型 ColorDrawable
    //创建一个什么也没有的Bitmap;
    Bitmap outBitmap = Bitmap.createBitmap(getMeasuredWidth(),
            getMeasuredHeight(), Bitmap.Config.ARGB_8888);
    Canvas canvas = new Canvas(outBitmap);
    //把drawable画到Bitmap上   --》将drawable绘制在canvas内部
    drawable.setBounds(0, 0, getMeasuredWidth(), getMeasuredHeight());
    drawable.draw(canvas);
    return outBitmap;
}

public void setShape(int shape) {
    mShape = shape;
}

public int getShape() {
    return mShape;
}

/**
 * 圆形
 *
 * @param bitmap
 * @return
 */
private Bitmap getCircleBitmap(Bitmap bitmap) {
    //创建一个Bitmap
    Bitmap circleBitmap = Bitmap.createBitmap(getMeasuredWidth(),
            getMeasuredHeight(), Bitmap.Config.ARGB_8888);
    Canvas canvas = new Canvas(circleBitmap);
    Paint paint = new Paint();
    paint.setAntiAlias(true);
    paint.setFilterBitmap(true);
    //防止抖动
    paint.setDither(true);
    //在画布上绘制一个圆
    canvas.drawCircle(getMeasuredWidth() / 2, getMeasuredHeight() / 2, getMeasuredWidth() / 2, paint);
    //设置画笔的图层,PorterDuff.Mode.SRC_IN 取图层交集的上层
    paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC_IN));
    //在把原来的bitmap绘制到圆上面
    canvas.drawBitmap(bitmap, 0, 0, paint);
    //回收Bitmap
    bitmap.recycle();
    return circleBitmap;
}

/**
 * 带圆角的矩形
 *
 * @param bitmap
 * @return
 */
private Bitmap getRecBitmap(Bitmap bitmap) {
    Bitmap recBitmap = Bitmap.createBitmap(getMeasuredWidth(), getMeasuredHeight(),
            Bitmap.Config.ARGB_8888);
    Canvas canvas = new Canvas(recBitmap);
    Paint paint = new Paint();
    paint.setAntiAlias(true);
    paint.setFilterBitmap(true);
    //防止抖动
    paint.setDither(true);
    //在画布上绘制一个圆角的矩形
    canvas.drawRoundRect(new RectF(0, 0, getMeasuredWidth(), getMeasuredHeight()),
            DensityUtil.dip2px(this.getContext(), 2), DensityUtil.dip2px(this.getContext(), 2), paint);
    //设置画笔的图层,PorterDuff.Mode.SRC_IN 取图层交集的上层
    paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC_IN));
    //在把原来的bitmap绘制到圆上面
    canvas.drawBitmap(bitmap, 0, 0, paint);
    //回收Bitmap
    bitmap.recycle();
    return recBitmap;
}
 }

一般底部会有两种类型指示器,一是矩形的,二是圆形的,这个类实现了如何自定义矩形和圆形指示器,其实这个类也可以实现圆形的和带圆角的矩形的图片,用PorterDuffXfermode图层的概念。

BannerAdapter类

public abstract class BannerAdapter {
    /**
     * 根据位置获取ViewPager的子View
     *
     * @param position
     * @return
     */
    public abstract View getView(int position, View convertView);

    /**
     * 返回数量
     *
     * @return
     */
    public abstract int getCount();
}

BannerAdapter这个类是轮播图的适配器,因为服务器返回的列表图片的url,显示的时候需要转成IamgeViw,用适配器设计模式转一下。

BannerViewPager类

public class BannerViewPager extends ViewPager {
    private static final String TAG = BannerViewPager.class.getSimpleName();
    private static final int SCROLL_MSG = 0x011;
    private BannerAdapter mBannerAdapter;
    private int mCutDownTime = 3000;
    private BannerScroller mBannerScroller;
    //内存优化界面复用
    private List<View> mConvertView;
    @SuppressLint("HandlerLeak")
    private Handler mHandler = new Handler() {
        @Override
        public void handleMessage(Message msg) {
            super.handleMessage(msg);
            switch (msg.what) {
                case SCROLL_MSG:
                    setCurrentItem(getCurrentItem() + 1);
                    startLoop();
                    break;
        }
    }
};

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

public BannerViewPager(Context context, AttributeSet attrs) {
    super(context, attrs);
    //改变ViewPager切换的速率
    try {
        //获取ViewPager的私有的属性mScroller
        Field field = ViewPager.class.getDeclaredField("mScroller");
        mBannerScroller = new BannerScroller(context);
        //设置强制改变
        field.setAccessible(true);
        //设置参数 第一个参数object当前属性的那个类 第二参数需要设置的值
        field.set(this, mBannerScroller);
    } catch (IllegalAccessException e) {
        e.printStackTrace();
    } catch (NoSuchFieldException e) {
        e.printStackTrace();
    }
    mConvertView = new ArrayList<>();
}

/**
 * 设置切换页面的持续时间
 *
 * @param scrollerDuration
 */
public void setScrollerDuration(int scrollerDuration) {
    mBannerScroller.setScrollerDuration(scrollerDuration);
}

public void setAdapter(BannerAdapter adapter) {
    this.mBannerAdapter = adapter;
    setAdapter(new BannerPagerAdapter());
    //管理Activity的生命周期
    (( Activity ) (getContext())).getApplication().registerActivityLifecycleCallbacks(mDefaultActivityLifecycleCallbacks);
}

/**
 * 开启轮播
 */
public void startLoop() {
    mHandler.removeMessages(SCROLL_MSG);
    mHandler.sendEmptyMessageDelayed(SCROLL_MSG, mCutDownTime);
}

/**
 * 销毁Handler
 */
@Override
protected void onDetachedFromWindow() {
    super.onDetachedFromWindow();
    mHandler.removeMessages(SCROLL_MSG);
    mHandler = null;

}

private class BannerPagerAdapter extends PagerAdapter {
    /**
     * 给一个很大的值,为了实现无限轮播
     * 这个方法是返回ViewPager有多少个View
     */
    @Override
    public int getCount() {
        return Integer.MAX_VALUE;
    }

    @NonNull
    @Override
    public Object instantiateItem(@NonNull ViewGroup container, int position) {
        //Adapter设计模式为了完全让用户自定义
        //position 0-2的31次方
        Log.i(TAG, "instantiateItem:position=" + position + "mBannerAdapter.getCount()=" + mBannerAdapter.getCount());
        //position % mBannerAdapter.getCount() 求模
        View bannerItemView = mBannerAdapter.getView(position % mBannerAdapter.getCount(), getConvertView());
        container.addView(bannerItemView);
        return bannerItemView;
    }

    @Override
    public boolean isViewFromObject(@NonNull View view, @NonNull Object object) {
        return view == object;
    }

    @Override
    public void destroyItem(@NonNull ViewGroup container, int position, @NonNull Object object) {
        container.removeView(( View ) object);
        mConvertView.add(( View ) object);
    }
}

private float mDownX;

@Override
public boolean onTouchEvent(MotionEvent ev) {
    switch (ev.getAction()) {
        case MotionEvent.ACTION_DOWN:
            mDownX = ev.getX();
            mHandler.removeMessages(SCROLL_MSG);
            break;
        case MotionEvent.ACTION_MOVE:
            break;
        case MotionEvent.ACTION_UP:
            //左滑动到第一张,跳转到getCount() - 1
            if (this.getCurrentItem() == 0) {
                if (ev.getX() - mDownX > 0) {
                    this.setCurrentItem(mBannerAdapter.getCount() - 1);
                    Log.i(TAG, "onTouchEvent: " + this.getCurrentItem());
                }
            }
            mHandler.sendEmptyMessageDelayed(SCROLL_MSG, mCutDownTime);

            break;
    }
    return super.onTouchEvent(ev);
}

/**
 * 处理页面复用
 *
 * @return
 */
public View getConvertView() {
    for (int i = 0; i < mConvertView.size(); i++) {
        if (mConvertView.get(i).getParent() == null) {
            return mConvertView.get(i);
        }
    }
    return null;
}

/**
 * 管理Activity的生命周期
 */
DefaultActivityLifecycleCallbacks mDefaultActivityLifecycleCallbacks = new DefaultActivityLifecycleCallbacks() {
    @Override
    public void onActivityResumed(Activity activity) {
        super.onActivityResumed(activity);
        if (activity == getContext()) {
            //开启轮播
            mHandler.sendEmptyMessageDelayed(SCROLL_MSG, mCutDownTime);
        }
    }

    @Override
    public void onActivityPaused(Activity activity) {
        super.onActivityPaused(activity);
        if (activity == getContext()) {
            //停止轮播
            mHandler.removeMessages(SCROLL_MSG);
        }
    }
};
}

继承PagerAdapter实现getCount()这个方法,这个方法返回的是ViewPager有多少个View。为了实现无限轮播图返回了Integer.MAX_VALUE,用户不会手残一直向右滑动吧,造成溢出吧,哈。DefaultActivityLifecycleCallbacks 去监听Activity的生命周期,为什么要监听呢?因为当用户点击home键的时候,此时应用会在后台,但是ViewPager里面的ImageView还会循环,所以在Activity执行onPaused()的时候,停止轮播。getConvertView()这个方法是处理界面复用的,意思是跟RecycleView或者ListView实现列表滑动一样的,需要界面复用。最后,小编想实现一个左滑动到position=0,也就是第一张的时候,想跳转到getCount-1张,具体的做法是想在onTouchEvent()方法监听,手指按下记录下mDownX,手指抬起的时候ev.getX(),用ev.getX() - mDownX > 0坐下判断。在设置下 setCurrentItem(mBannerAdapter.getCount() - 1);
发现并没有实现。也不知道这是为什么,但是我认为这种思路没错,哪位大神看到了,请给出具体解决方案。

BannerView类

public class BannerView extends RelativeLayout {
    private BannerViewPager mBannerViewPager;
    //底部的指示器的View
    private LinearLayout mDotContainerView;
    //适配器
    private BannerAdapter mAdapter;
    private Context mContext;
    //选中的drawable
    private Drawable mIndicatorFocusDrawable;
    //未被选中的drawable
    private Drawable mIndicatorNormalDrawable;
    //当前页面的位置
    private int mCurrentPosition;
    //指示器的位置
    private int mDotGravity = -1;
    //指示器的大小
    private int mDotSize = 6;
    //指示器的间距
    private int mDotDistance = 2;
    //底部颜色默认透明
    private int mBottomColor = Color.TRANSPARENT;
    private View mBannerBottomView;

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

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

    public BannerView(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        inflate(context, R.layout.banner_layout, this);
        this.mContext = context;
        initAttribute(attrs);
        initView();

    }

    /**
     * 初始化自定义属性
     *
     * @param attrs
     */
    private void initAttribute(AttributeSet attrs) {
        TypedArray typedArray = mContext.obtainStyledAttributes(attrs, R.styleable.BannerView);
        mDotGravity = typedArray.getInt(R.styleable.BannerView_dotGravity, -1);
        mIndicatorFocusDrawable = typedArray.getDrawable(R.styleable.BannerView_dotIndicatorFocus);
        if (mIndicatorFocusDrawable == null) {
            mIndicatorFocusDrawable = new ColorDrawable(Color.RED);
        }
        mIndicatorNormalDrawable = typedArray.getDrawable(R.styleable.BannerView_dotIndicatorNormal);
        if (mIndicatorNormalDrawable == null) {
            mIndicatorNormalDrawable = new ColorDrawable(Color.WHITE);
        }
        mDotSize = ( int ) typedArray.getDimension(R.styleable.BannerView_dotSize, DensityUtil.dip2px(mContext, 6));
        mDotDistance = ( int ) typedArray.getDimension(R.styleable.BannerView_dotDistance, DensityUtil.dip2px(mContext, 2));
        mBottomColor = typedArray.getColor(R.styleable.BannerView_bottomColor, mBottomColor);

        typedArray.recycle();
    }

    /**
     * 初始化View
     */
    private void initView() {
        mBannerViewPager = findViewById(R.id.bannerViewPager);
        mDotContainerView = findViewById(R.id.dot_container);
        mBannerBottomView = findViewById(R.id.bannerBottomView);
        mBannerBottomView.setBackgroundColor(mBottomColor);
        mBannerViewPager.setPageTransformer(false, new SlidePageTransformer());
    }

    /**
     * 设置适配器adapter
     *
     * @param adapter 适配器
     */
    public void setAdapter(BannerAdapter adapter) {
        this.mAdapter = adapter;
        mBannerViewPager.setAdapter(adapter);
        mBannerViewPager.setCurrentItem(mBannerViewPager.getChildCount() / 2);
        initDotIndicator();
        mBannerViewPager.addOnPageChangeListener(new ViewPager.SimpleOnPageChangeListener() {
            @Override
            public void onPageSelected(int position) {
                //监听下当前的位置
                super.onPageSelected(position);
                DotIndicatorView dotIndicatorView = ( DotIndicatorView ) mDotContainerView.
                        getChildAt(mCurrentPosition);
                dotIndicatorView.setDrawable(mIndicatorNormalDrawable);
                mCurrentPosition = position % mAdapter.getCount();
                DotIndicatorView mCurrentIndicatorView = ( DotIndicatorView ) mDotContainerView.
                        getChildAt(mCurrentPosition);
                mCurrentIndicatorView.setDrawable(mIndicatorFocusDrawable);
            }
        });
    }

    public void startLoop() {
        mBannerViewPager.startLoop();
    }

    public void setScrollerDuration(int scrollerDuration) {
        mBannerViewPager.setScrollerDuration(scrollerDuration);
    }

    /**
     * 初始化指示器
     */
    private void initDotIndicator() {
        //获取广告位的数量
        int count = mAdapter.getCount();
        //设置指示器的位置
        mDotContainerView.setGravity(getDotGravity());
        for (int i = 0; i < count; i++) {
            DotIndicatorView dot = new DotIndicatorView(mContext);
            //设置指示器的形状
            dot.setShape(1);
            LinearLayout.LayoutParams param = null;
            //矩形
            if (dot.getShape() == 1) {
                //给指示器指定大小
                param = new LinearLayout.LayoutParams(mDotSize * 3, DensityUtil.dip2px(this.getContext(), 2));
                //圆形
            } else if (dot.getShape() == 2) {
                param = new LinearLayout.LayoutParams(mDotSize, mDotSize);
            }
            //设置间距
            param.leftMargin = param.rightMargin = mDotDistance;
            dot.setLayoutParams(param);
            if (i == 0) {
                dot.setDrawable(mIndicatorFocusDrawable);
            } else {
                dot.setDrawable(mIndicatorNormalDrawable);
            }
            mDotContainerView.addView(dot);
        }
    }

    public int getDotGravity() {
        switch (mDotGravity) {
            case 0:
                return Gravity.CENTER;
            case 1:
                return Gravity.RIGHT;
            case -1:
                return Gravity.LEFT;
        }
        return Gravity.RIGHT;
    }

SlidePageTransformer类

public class SlidePageTransformer implements ViewPager.PageTransformer {
@Override 
public void transformPage(@NonNull View page, float position) {
    if (position > 0 && position <= 1) {
        page.setPivotX(0);
        page.setScaleX(1 - position);
    } else if (position >= -1 && position < 0) {
        page.setPivotX(page.getWidth());
        page.setScaleX(1 + position);
    } 
} 
} 

BannerView这个类主要是一些自定义属性,底部指示器的大小、颜色、间距等等。主要说下这个 mBannerViewPager.setPageTransformer(false, new SlidePageTransformer());这个给ViewPager设置了一个平滑的缩放的动画,但是看到了一个ViewPager设置动画的一个坑,发现滑到第一张的时候,在向右滑动的时候,图片会滑出一点边缘。也不知道为什么?我认为我的代码没有问题,也听说Android的源码ViewPager去设置动画,会有坑的存在。哪位大神看到了,望赐教!

项目的完整代码https://github.com/StevenYan88/BannerView

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