解析ScrollView--仿QQ空间标题栏渐变

先看一下效果图：

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="com.hankkin.gradationtitlebar.QQSpeakActivity">

<com.hankkin.gradationscroll.GradationScrollView
 android:id="@+id/scrollview"
 android:layout_width="match_parent"
 android:layout_height="match_parent"
 android:scrollbars="none">
 <LinearLayout
  android:layout_width="match_parent"
  android:layout_height="wrap_content"
  android:orientation="vertical" >
  <ImageView
   android:id="@+id/iv_banner"
   android:scaleType="fitXY"
   android:src="@drawable/banner3"
   android:layout_width="match_parent"
   android:layout_height="200dp" />
  <com.hankkin.gradationscroll.NoScrollListview
   android:id="@+id/listview"
   android:layout_width="match_parent"
   android:layout_height="wrap_content" >
  </com.hankkin.gradationscroll.NoScrollListview>
 </LinearLayout>
</com.hankkin.gradationscroll.GradationScrollView>
<TextView
 android:paddingBottom="10dp"
 android:id="@+id/textview"
 android:layout_width="match_parent"
 android:layout_height="55dp"
 android:gravity="center|bottom"
 android:text="我是标题"
 android:textSize="18sp"
 android:textColor="@color/transparent"
 android:background="#00000000" />
</RelativeLayout>

public class GradationScrollView extends ScrollView {

public interface ScrollViewListener {
 void onScrollChanged(GradationScrollView scrollView, int x, int y,
       int oldx, int oldy);
}

private ScrollViewListener scrollViewListener = null;

public GradationScrollView(Context context) {
 super(context);
}

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

public GradationScrollView(Context context, AttributeSet attrs) {
 super(context, attrs);
}

public void setScrollViewListener(ScrollViewListener scrollViewListener) {
 this.scrollViewListener = scrollViewListener;
}
@Override
protected void onScrollChanged(int x, int y, int oldx, int oldy) {
 super.onScrollChanged(x, y, oldx, oldy);
 if (scrollViewListener != null) {
  scrollViewListener.onScrollChanged(this, x, y, oldx, oldy);
 }
}
}

我们需要获取图片的高度，并且设置滚动监听，随着滚动的距离来设置标题栏的颜色透明度和字体颜色的透明度

/**
* 获取顶部图片高度后，设置滚动监听
*/
private void initListeners() {
 ViewTreeObserver vto = ivBanner.getViewTreeObserver();
 vto.addOnGlobalLayoutListener(new ViewTreeObserver.OnGlobalLayoutListener() {
  @Override
  public void onGlobalLayout() {
   textView.getViewTreeObserver().removeGlobalOnLayoutListener(
     this);
   height = ivBanner.getHeight();

scrollView.setScrollViewListener(QQSpeakActivity.this);
  }
 });
}

/**
 * 滑动监听
 * @param scrollView
 * @param x
 * @param y
 * @param oldx
 * @param oldy
*/
@Override
public void onScrollChanged(GradationScrollView scrollView, int x, int y,
       int oldx, int oldy) {
 // TODO Auto-generated method stub
 if (y <= 0) { //设置标题的背景颜色
  textView.setBackgroundColor(Color.argb((int) 0, 144,151,166));
 } else if (y > 0 && y <= height) { //滑动距离小于banner图的高度时，设置背景和字体颜色颜色透明度渐变
  float scale = (float) y / height;
  float alpha = (255 * scale);
  textView.setTextColor(Color.argb((int) alpha, 255,255,255));
  textView.setBackgroundColor(Color.argb((int) alpha, 144,151,166));
 } else { //滑动到banner下面设置普通颜色
  textView.setBackgroundColor(Color.argb((int) 255, 144,151,166));
 }
}

来源：http://www.cnblogs.com/ganchuanpu/p/6790680.html