android翻页效果实现

[android]代码库
package com.astuetz.viewpager.extensions;
 
import android.content.Context;
import android.content.res.TypedArray;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.os.AsyncTask;
import android.support.v4.view.ViewPager;
import android.support.v4.view.ViewPager.OnPageChangeListener;
import android.util.AttributeSet;
import android.view.View;
 
 
public class IndicatorLineView extends View implements OnPageChangeListener {
     
    @SuppressWarnings("unused")
    private static final String TAG = "com.astuetz.viewpager.extensions";
     
    private ViewPager mPager;
     
    private int mLineColor = 0xFF34B5E8;
     
    private float mLineLeft = 0.0f;
    private float mLineWidth = 0.0f;
     
    private int mFadeOutTime = 500;
    private int mFadingDuration = 200;
     
    private int mAlpha = 0xFF;
     
    private FadeTimer mTimer;
     
     
    public IndicatorLineView(Context context) {
        this(context, null);
    }
     
    public IndicatorLineView(Context context, AttributeSet attrs) {
        this(context, attrs, 0);
    }
     
    public IndicatorLineView(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
         
        final TypedArray a = context.obtainStyledAttributes(attrs, R.styleable.ViewPagerExtensions, defStyle, 0);
         
        mLineColor = a.getColor(R.styleable.ViewPagerExtensions_lineColor, mLineColor);
         
        mFadeOutTime = a.getInt(R.styleable.ViewPagerExtensions_fadeOutDelay, mFadeOutTime);
         
        mFadingDuration = a.getInt(R.styleable.ViewPagerExtensions_fadeOutDuration, mFadingDuration);
         
        a.recycle();
    }
     
    @Override
    protected void onSizeChanged(int w, int h, int oldw, int oldh) {
        if (mPager != null) {
            mLineWidth = w / mPager.getAdapter().getCount();
            mLineLeft = mLineWidth * mPager.getCurrentItem();
            invalidate();
            resetTimer();
        }
    }
     
     
     
    public void setViewPager(ViewPager pager) {
        this.mPager = pager;
        mPager.setOnPageChangeListener(this);
    }
     
     
    private Paint mLinePaint = new Paint();
     
    protected synchronized void onDraw(Canvas canvas) {
         
        super.onDraw(canvas);
         
        final Paint linePaint = mLinePaint;
         
        final int color = Color.argb(mAlpha, Color.red(mLineColor), Color.green(mLineColor), Color.blue(mLineColor));
         
        linePaint.setColor(color);
         
        // draw the line
        canvas.drawRect(mLineLeft, 0, mLineLeft + mLineWidth, getMeasuredHeight(), linePaint);
         
    }
     
     
     
 
    public void onPageScrollStateChanged(int state) {}
     
 
    public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
         
        final float currentX = mPager.getScrollX();
        final float fullX = (mPager.getWidth() + mPager.getPageMargin()) * (mPager.getAdapter().getCount());
         
        mLineLeft = getMeasuredWidth() * currentX / fullX;
         
        mLineWidth = getMeasuredWidth() / mPager.getAdapter().getCount();
         
        resetTimer();
         
        invalidate();
         
    }
     
 
    public void onPageSelected(int position) {}
     
     
     
    public void setLineColor(int lineColor) {
        this.mLineColor = lineColor;
        invalidate();
    }
     
    public int getLineColor() {
        return this.mLineColor;
    }
     
    public void setFadeOutDelay(int milliseconds) {
        this.mFadeOutTime = milliseconds;
        invalidate();
    }
     
    public int getFadeOutDelay() {
        return this.mFadeOutTime;
    }
     
    public void setFadeOutDuration(int milliseconds) {
        this.mFadingDuration = milliseconds;
        invalidate();
    }
     
    public int getFadeOutDuration() {
        return this.mFadingDuration;
    }
     
     
     
    private void setAlpha(int alpha) {
        this.mAlpha = alpha;
        invalidate();
    }
     
    private void resetTimer() {
         
        if (mFadeOutTime > 0) {
             
            if (mTimer == null || mTimer.isRunning == false) {
                mTimer = new FadeTimer();
                mTimer.execute();
            } else {
                mTimer.reset();
            }
             
            mAlpha = 0xFF;
             
        }
         
    }
     
    private class FadeTimer extends AsyncTask<Void, Integer, Void> {
         
        private int elapsed = 0;
        private boolean isRunning = true;
         
        public void reset() {
            elapsed = 0;
        }
         
        @Override
        protected Void doInBackground(Void... args) {
            while (isRunning) {
                try {
                    Thread.sleep(1);
                    elapsed++;
                     
                    if (elapsed >= mFadeOutTime && elapsed < mFadeOutTime + mFadingDuration) {
                         
                        int x0 = mFadeOutTime;
                        int x1 = mFadeOutTime + mFadingDuration;
                        int x = elapsed;
                        int y0 = 0xFF;
                        int y1 = 0x00;
                         
                        int a = y0 + ((x - x0) * y1 - (x - x0) * y0) / (x1 - x0);
                        publishProgress(a);
                    }
                    else if (elapsed >= mFadeOutTime + mFadingDuration) {
                        isRunning = false;
                    }
                     
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
            return null;
        }
         
        protected void onProgressUpdate(Integer... alpha) {
            setAlpha(alpha[0]);
        }
         
        @Override
        protected void onPostExecute(Void result) {
            setAlpha(0x00);
        }
    }
     
}
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