//這個監聽有三個方法public abstract void onPageScrollStateChanged (int state) public abstract void onPageScrolled (int position, float positionOffset, int positionOffsetPixels) public abstract void onPageSelected (int position) //第一個方法onPageScrollStateChanged 中的參數state，有三個可取的值public static final int SCROLL_STATE_DRAGGING Constant Value: 1 (0x00000001) //手指按在ViewPager上滑動時public static final int SCROLL_STATE_IDLE Constant Value: 0 (0x00000000) //手指松開后，ViewPager自動滑動期間public static final int SCROLL_STATE_SETTLING Constant Value: 2 (0x00000002) //ViewPager進入了某個Page//如果在onPageScrollStateChanged 中輸出state的值，你會發現每次都是按順序打印出“1---2---0”//第二個方法onPageScrolled的三個參數position：//滑動時，屏幕左側顯示的第一個pagepositionOffset：//滑動比例，值的范圍為[0, 1)，手指往左滑動，該值遞增，反之遞減positionOffsetPixels：//滑動距離，和屏幕有關，手指往左滑動，該值遞增，反之遞減//我們經常需要檢查viewpager的滑動方向并作出一些操作，這時你只需要通過position和positionOffset兩個值即可實現該功能。//比如實現微信底部圖標顏色漸變 向左滑動時ChangeColorIconWithTextView left = mTabIndicator.get(position); //左側顯示的第一個page頁面上底部圖標和文字的初始化ChangeColorIconWithTextView right = mTabIndicator.get(position + 1); //右側顯示的Page底部圖標和文字的初始化left.setIconAlpha(1 - positionOffset); //設置圖標的透明度 此時positionOffset值遞增 左側圖標的顏色變淺right.setIconAlpha(positionOffset); //右側圖標的顏色逐漸變深//第三個方法onPageSelected的三個參數position：//當前選擇的page序號//該方法被調用的時間比較特別，在上面的第一個方法中的“1---2----0”中的2執行之后，onPageSelected就執行，然后執行“1---2----0”中的0。就是手指松開屏幕之后，onPageSelected被執行。

package com.mhealth.nursestation.app.pda.business.login.base.ui.fragmentutil;import android.content.Context;import android.content.res.TypedArray;import android.graphics.Bitmap;import android.graphics.Bitmap.Config;import android.graphics.BitmapFactory;import android.graphics.Canvas;import android.graphics.Paint;import android.graphics.PorterDuff;import android.graphics.PorterDuffXfermode;import android.graphics.Rect;import android.graphics.drawable.BitmapDrawable;import android.os.Bundle;import android.os.Looper;import android.os.Parcelable;import android.util.AttributeSet;import android.util.TypedValue;import android.view.View;import com.mhealth.nursestation.app.pda.R;/** * 此類用于修改顏色漸變 */public class ChangeColorIconWithTextView extends View {  private Bitmap mBitmap;  private Canvas mCanvas;  private Paint mPaint;  /**   * 顏色   */  private int mColor = 0XFF07B7C4;  /**   * 透明度 0.0-1.0 初始化必須是0 不是0就廢了   */  private float mAlpha = 0f;  /**   * 圖標   */  private Bitmap mIconBitmap;  /**   * 限制繪制icon的范圍   */  private Rect mIconRect;  /**   * icon底部文本   */  private String mText = "微信";  private int mTextSize = (int) TypedValue.applyDimension(      TypedValue.COMPLEX_UNIT_SP, 10, getResources().getDisplayMetrics());  private Paint mTextPaint;  private Rect mTextBound = new Rect();  public ChangeColorIconWithTextView(Context context) {    super(context);  }  /**   * 初始化自定義屬性值   *    * @param context   * @param attrs   */  public ChangeColorIconWithTextView(Context context, AttributeSet attrs) {    super(context, attrs);    // 獲取設置的圖標    TypedArray a = context.obtainStyledAttributes(attrs,        R.styleable.ChangeColorIconView);    int n = a.getIndexCount();    for (int i = 0; i < n; i++) {      int attr = a.getIndex(i);      switch (attr) {      case R.styleable.ChangeColorIconView_icon:        BitmapDrawable drawable = (BitmapDrawable) a.getDrawable(attr);        mIconBitmap = drawable.getBitmap();        break;      case R.styleable.ChangeColorIconView_color:        mColor = a.getColor(attr, 0x07B7C4);        break;      case R.styleable.ChangeColorIconView_text:        mText = a.getString(attr);        break;      case R.styleable.ChangeColorIconView_text_size:        mTextSize = (int) a.getDimension(attr, TypedValue            .applyDimension(TypedValue.COMPLEX_UNIT_SP, 10,                getResources().getDisplayMetrics()));        break;      }    }    a.recycle();    mTextPaint = new Paint();    mTextPaint.setTextSize(mTextSize);    mTextPaint.setColor(0xff07B7C4);    mTextPaint.setAntiAlias(true);     // 得到text繪制范圍    mTextPaint.getTextBounds(mText, 0, mText.length(), mTextBound);  }  @Override  protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {    super.onMeasure(widthMeasureSpec, heightMeasureSpec);    // 得到繪制icon的寬    int bitmapWidth = Math.min(getMeasuredWidth() - getPaddingLeft()        - getPaddingRight(), getMeasuredHeight() - getPaddingTop()        - getPaddingBottom() - mTextBound.height());    int left = getMeasuredWidth() / 2 - bitmapWidth / 2;    int top = (getMeasuredHeight() - mTextBound.height()) / 2 - bitmapWidth        / 2;    // 得到繪制icon的寬    mIconRect = new Rect(left, top, left + bitmapWidth, top + bitmapWidth);  }  @Override  protected void onDraw(Canvas canvas) {    int alpha = (int) Math.ceil((255 * mAlpha));    canvas.drawBitmap(mIconBitmap, null, mIconRect, null);    setupTargetBitmap(alpha);    drawSourceText(canvas, alpha);    drawTargetText(canvas, alpha);    canvas.drawBitmap(mBitmap, 0, 0, null);  }  private void setupTargetBitmap(int alpha) {    mBitmap = Bitmap.createBitmap(getMeasuredWidth(), getMeasuredHeight(),        Config.ARGB_8888);    mCanvas = new Canvas(mBitmap);    mPaint = new Paint();    mPaint.setColor(mColor);    mPaint.setAntiAlias(true);    mPaint.setDither(true);    mPaint.setAlpha(alpha);    mCanvas.drawRect(mIconRect, mPaint);    mPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.DST_IN));    mPaint.setAlpha(255);    mCanvas.drawBitmap(mIconBitmap, null, mIconRect, mPaint);  }  /**   * 透明度 255   *    * @param canvas   * @param alpha   */  private void drawSourceText(Canvas canvas, int alpha) {    mTextPaint.setTextSize(mTextSize);    mTextPaint.setColor(0x00333333);    mTextPaint.setAlpha(255 - alpha);    canvas.drawText(mText, mIconRect.left + mIconRect.width() / 2        - mTextBound.width() / 2,        mIconRect.bottom + mTextBound.height(), mTextPaint);  }  private void drawTargetText(Canvas canvas, int alpha) {    mTextPaint.setColor(mColor);    mTextPaint.setAlpha(alpha);    canvas.drawText(mText, mIconRect.left + mIconRect.width() / 2        - mTextBound.width() / 2,        mIconRect.bottom + mTextBound.height(), mTextPaint);  }  public void setIconAlpha(float alpha) {    this.mAlpha = alpha;    invalidateView();  }  private void invalidateView() {    if (Looper.getMainLooper() == Looper.myLooper()) {      invalidate();    } else {      postInvalidate();    }  }  public void setIconColor(int color) {    mColor = color;  }  public void setIcon(int resId) {    this.mIconBitmap = BitmapFactory.decodeResource(getResources(), resId);    if (mIconRect != null)      invalidateView();  }  public void setIcon(Bitmap iconBitmap) {    this.mIconBitmap = iconBitmap;    if (mIconRect != null)      invalidateView();  }  private static final String INSTANCE_STATE = "instance_state";  private static final String STATE_ALPHA = "state_alpha";  @Override  protected Parcelable onSaveInstanceState() {    Bundle bundle = new Bundle();    bundle.putParcelable(INSTANCE_STATE, super.onSaveInstanceState());    bundle.putFloat(STATE_ALPHA, mAlpha);    return bundle;  }  @Override  protected void onRestoreInstanceState(Parcelable state) {    if (state instanceof Bundle) {      Bundle bundle = (Bundle) state;      mAlpha = bundle.getFloat(STATE_ALPHA);      super.onRestoreInstanceState(bundle.getParcelable(INSTANCE_STATE));    } else {      super.onRestoreInstanceState(state);    }  }}

@Override  public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {    if (positionOffset > 0) {      ChangeColorIconWithTextView left = mTabIndicator.get(position);      ChangeColorIconWithTextView right = mTabIndicator.get(position + 1);      left.setIconAlpha(1 - positionOffset);      right.setIconAlpha(positionOffset);    }  }

private List<ChangeColorIconWithTextView> mTabIndicator = new ArrayList<ChangeColorIconWithTextView>();private void initTabIndicator() {    ChangeColorIconWithTextView one = (ChangeColorIconWithTextView) findViewById(R.id.id_indicator_one);    ChangeColorIconWithTextView two = (ChangeColorIconWithTextView) findViewById(R.id.id_indicator_two);    ChangeColorIconWithTextView three = (ChangeColorIconWithTextView) findViewById(R.id.id_indicator_three);    ChangeColorIconWithTextView four = (ChangeColorIconWithTextView) findViewById(R.id.id_indicator_four);    mTabIndicator.add(one);    mTabIndicator.add(two);    mTabIndicator.add(three);    mTabIndicator.add(four);    one.setOnClickListener(this);    two.setOnClickListener(this);    three.setOnClickListener(this);    four.setOnClickListener(this);    one.setIconAlpha(1.0f);  }

@Override  public void onClick(View v) {    resetOtherTabs();    switch (v.getId()) {    case R.id.id_indicator_one:      mTabIndicator.get(0).setIconAlpha(1.0f);      mViewPager.setCurrentItem(0, false);      break;    case R.id.id_indicator_two:      mTabIndicator.get(1).setIconAlpha(1.0f);      mViewPager.setCurrentItem(1, false);      break;    case R.id.id_indicator_three:      mTabIndicator.get(2).setIconAlpha(1.0f);      mViewPager.setCurrentItem(2, false);      mAppContext.has_new_talk = false;      break;    case R.id.id_indicator_four:      mTabIndicator.get(3).setIconAlpha(1.0f);      mViewPager.setCurrentItem(3, false);      break;    }  }