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)】

还不懂的童鞋可以下载源代码：http://download.csdn.net/detail/sinat_21283073/9510052