android标题栏颜色渐变效果的实现(标题栏随着scrollview的滚动而变化)

之前也是在网上看到这种效果，不过是滚动listview来改变标题栏的颜色，感觉那个应用的比较少，比如我要滚动scrollview来实现呢，那么问题就来了，废话少说，看一下要实现的效果先(这是在项目应用的效果)。

直接上源代码：

【一、核心类(ObservableScrollView.java)】

 package com.jukopro.titlebarcolor;

 import android.content.Context;
 import android.util.AttributeSet;
 import android.widget.ScrollView;
 /**
  * 带滚动监听的scrollview
  *
  */
 public class ObservableScrollView extends ScrollView {

     public interface ScrollViewListener {

         void onScrollChanged(ObservableScrollView scrollView, int x, int y,
                 int oldx, int oldy);

     }

     private ScrollViewListener scrollViewListener = null;

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

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

     public ObservableScrollView(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);
         }
     }

 }

【二、具体使用(MainActivity.java)】

 package com.jukopro.titlebarcolor;

 import android.app.Activity;
 import android.graphics.Color;
 import android.os.Bundle;
 import android.view.ViewTreeObserver;
 import android.view.ViewTreeObserver.OnGlobalLayoutListener;
 import android.widget.ArrayAdapter;
 import android.widget.ImageView;
 import android.widget.ListView;
 import android.widget.TextView;

 import com.jukopro.titlebarcolor.ObservableScrollView.ScrollViewListener;

 public class MainActivity extends Activity implements ScrollViewListener{

     private ObservableScrollView scrollView;

     private ListView listView;

     private ImageView imageView;

     private TextView textView;

     private int imageHeight;

     @Override
     protected void onCreate(Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
         setContentView(R.layout.activity_main);
         scrollView = (ObservableScrollView) findViewById(R.id.scrollview);
         listView = (ListView) findViewById(R.id.listview);
         imageView = (ImageView) findViewById(R.id.imageview);
         textView = (TextView) findViewById(R.id.textview);
         initListeners();
         initData();
     }

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

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



     private void initData() {
         ArrayAdapter adapter = new ArrayAdapter(MainActivity.this, android.R.layout.simple_list_item_1, getResources().getStringArray(R.array.data));
         listView.setAdapter(adapter);
     }



     @Override
     public void onScrollChanged(ObservableScrollView scrollView, int x, int y,
             int oldx, int oldy) {
         // TODO Auto-generated method stub
         // Log.i("TAG", "y--->" + y + "    height-->" + height);
         if (y <= 0) {
             textView.setBackgroundColor(Color.argb((int) 0, 227, 29, 26));//AGB由相关工具获得，或者美工提供
         } else if (y > 0 && y <= imageHeight) {
             float scale = (float) y / imageHeight;
             float alpha = (255 * scale);
             // 只是layout背景透明(仿知乎滑动效果)
             textView.setBackgroundColor(Color.argb((int) alpha, 227, 29, 26));
         } else {
             textView.setBackgroundColor(Color.argb((int) 255, 227, 29, 26));
         }
     }
 }

【二、XML(activity_main.xml)】

 <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="${relativePackage}.${activityClass}" >

     <com.jukopro.titlebarcolor.ObservableScrollView
         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/imageview"
                 android:layout_width="match_parent"
                 android:layout_height="200dp"
                 android:background="@drawable/zuqiu" />

             <com.jukopro.titlebarcolor.MyListview
                 android:id="@+id/listview"
                 android:layout_width="match_parent"
                 android:layout_height="wrap_content" >
             com.jukopro.titlebarcolor.MyListview>
         LinearLayout>
     com.jukopro.titlebarcolor.ObservableScrollView>

     <TextView
         android:id="@+id/textview"
         android:layout_width="match_parent"
         android:layout_height="48dp"
         android:gravity="center"
         android:text="我是标题"
         android:textSize="18sp"
         android:textColor="@android:color/white"
         android:background="#00000000" />

 RelativeLayout>