Android开发实现标题随scrollview滑动变色的方法详解

<FrameLayout
    android:layout_width="match_parent"
    android:layout_height="match_parent">
    <com.****.ScrollChangeScrollView
      android:id="@+id/scrollView"
      android:layout_width="match_parent"
      android:layout_height="match_parent"
      android:fillViewport="true">
      <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical">
          <TextView
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:drawablePadding="5dp"
            android:drawableTop="@drawable/dicovery_vintner_icon_wine"
            android:gravity="center"
            android:text="葡萄酒"
            android:textColor="@color/hometitlebg" />
      </LinearLayout>
    </com.***.ScrollChangeScrollView>
    <Button
      android:id="@+id/btn_back"
      android:layout_width="match_parent"
      android:layout_height="35dp"
      android:layout_centerVertical="true"
      android:background="@null"
      android:drawableLeft="@drawable/icon_back"
      android:padding="10dp" />
</FrameLayout>

private View mTitleView;
/**
* 变色标题view
* @param view
*/
public void setupTitleView (View view) {
    this.mTitleView = view;
}

private View mByWhichView;
/**
* 跟随的view
* @param view
*/
public void setupByWhichView(View view) {
    mByWhichView = view;
}

private boolean shouldSlowlyChange;
public void setShouldSlowlyChange(boolean slowlyChange) {
    this.shouldSlowlyChange = slowlyChange;
}

**
 * 滑动时标题变色view
 * Created by george.yang on 16/2/21.
 */
public class ScrollChangeScrollView extends ScrollView {
  private View mByWhichView;
  private View mTitleView;
  private boolean shouldSlowlyChange = true;
  public ScrollChangeScrollView(Context context) {
    super(context);
  }
  public ScrollChangeScrollView(Context context, AttributeSet attrs) {
    super(context, attrs);
  }
  public ScrollChangeScrollView(Context context, AttributeSet attrs, int defStyleAttr) {
    super(context, attrs, defStyleAttr);
  }
  @TargetApi(Build.VERSION_CODES.LOLLIPOP)
  public ScrollChangeScrollView(Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes) {
    super(context, attrs, defStyleAttr, defStyleRes);
  }
  @Override
  public void scrollTo(int x, int y) {
    //这是为了修复noScrllListView嵌套在srcollview时就自动滑动到noscrolllistview的顶部的bug，不影响使用
    if (x == 0 && y == 0 || y <= 0) {
      super.scrollTo(x, y);
    }
  }
  public void setListener(OnScrollListener listener){
    this.mListener = listener;
  }
  public void setShouldSlowlyChange(boolean slowlyChange) {
    this.shouldSlowlyChange = slowlyChange;
  }
  /**
   * 设置透明度渐变的标题view
   * @param view
   */
  public void setupTitleView (View view) {
    this.mTitleView = view;
  }
  /**
   * 跟随的view
   * @param view
   */
  public void setupByWhichView(View view) {
    mByWhichView = view;
  }
  @Override
  protected void onOverScrolled(int scrollX, int scrollY, boolean clampedX,
                 boolean clampedY) {
    super.onOverScrolled(scrollX, scrollY, clampedX, clampedY);
    if (scrollY >= mByWhichView.getTop() + mByWhichView.getMeasuredHeight()) {
      mTitleView.setBackgroundColor(Color.BLACK);
    } else if (scrollY>=0) {
      if (!shouldSlowlyChange) {
        mTitleView.setBackgroundColor(Color.TRANSPARENT);
      } else {
        float persent = scrollY * 1f / (mByWhichView.getTop() + mByWhichView.getMeasuredHeight());
        int alpha = (int) (255 * persent);
        int color = Color.argb(alpha,0,0,0);
        mTitleView.setBackgroundColor(color);
      }
    }
    if (mListener!=null) {
      mListener.onScroll(scrollX, scrollY);
    }
  }
}