【转】重写ScrollView实现两个ScrollView的同步滚动显示

我们首先想到使用ScrollView的类似与setOnScrollChangedListener的方法来实现，当一个ScrollView滚动时，触发该方法进而使另外一个ScrollView滚动。不过很遗憾，谷歌没有提供该方法。通过查询相应的源代码，我们发现该方法的原型

protected void onScrollChanged(int x, int y, int oldx, int oldy)  

该方法是protected类型，不能直接调用，于是需要重新实现ScrollView

首先，定一个一个接口（ScrollViewListener.java）：

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

 我们需要重写ScrollView才能实现该借口，因此有下面的代码（ObservableScrollView.java）：

package com.devin;

import android.content.Context;
import android.util.AttributeSet;
import android.widget.ScrollView;

public class ObservableScrollView extends ScrollView {

    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);
        }
    }

}

接下来是界面的XML，这里是一个简单的Demo，如下(main.xml):    

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:background="#ffffff"
    android:orientation="horizontal" >

    <com.devin.ObservableScrollView
        android:id="@+id/scrollview1"
        android:layout_width="400dp"
        android:layout_height="wrap_content" >

        <LinearLayout
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:orientation="vertical" >

            <TextView
                android:layout_width="wrap_content"
                android:layout_height="200dp"
                android:layout_weight="1"
                android:text="monday"
                android:textColor="#000000" />

            <TextView
                android:layout_width="wrap_content"
                android:layout_height="200dp"
                android:layout_weight="1"
                android:text="tuesday"
                android:textColor="#000000" />

            <TextView
                android:layout_width="wrap_content"
                android:layout_height="200dp"
                android:layout_weight="1"
                android:text="wednesday"
                android:textColor="#000000" />

            <TextView
                android:layout_width="wrap_content"
                android:layout_height="200dp"
                android:layout_weight="1"
                android:text="thursday"
                android:textColor="#000000" />

            <TextView
                android:layout_width="wrap_content"
                android:layout_height="200dp"
                android:layout_weight="1"
                android:text="friday"
                android:textColor="#000000" />

            <TextView
                android:layout_width="wrap_content"
                android:layout_height="200dp"
                android:layout_weight="1"
                android:text="saturday"
                android:textColor="#000000" />

            <TextView
                android:layout_width="wrap_content"
                android:layout_height="200dp"
                android:layout_weight="1"
                android:text="sunday"
                android:textColor="#000000" />
        </LinearLayout>
    </com.devin.ObservableScrollView>

    <com.devin.ObservableScrollView
        android:id="@+id/scrollview2"
        android:layout_width="400dp"
        android:layout_height="wrap_content" >

        <LinearLayout
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:orientation="vertical" >

            <TextView
                android:layout_width="wrap_content"
                android:layout_height="200dp"
                android:layout_weight="1"
                android:text="monday"
                android:textColor="#000000" />

            <TextView
                android:layout_width="wrap_content"
                android:layout_height="200dp"
                android:layout_weight="1"
                android:text="tuesday"
                android:textColor="#000000" />

            <TextView
                android:layout_width="wrap_content"
                android:layout_height="200dp"
                android:layout_weight="1"
                android:text="wednesday"
                android:textColor="#000000" />

            <TextView
                android:layout_width="wrap_content"
                android:layout_height="200dp"
                android:layout_weight="1"
                android:text="thursday"
                android:textColor="#000000" />

            <TextView
                android:layout_width="wrap_content"
                android:layout_height="200dp"
                android:layout_weight="1"
                android:text="friday"
                android:textColor="#000000" />

            <TextView
                android:layout_width="wrap_content"
                android:layout_height="200dp"
                android:layout_weight="1"
                android:text="saturday"
                android:textColor="#000000" />

            <TextView
                android:layout_width="wrap_content"
                android:layout_height="200dp"
                android:layout_weight="1"
                android:text="sunday"
                android:textColor="#000000" />
        </LinearLayout>
    </com.devin.ObservableScrollView>

</LinearLayout>

最后是我们的主程调用（PadTestActivity.java）：

package com.devin;

import android.app.Activity;
import android.os.Bundle;

public class PadTestActivity extends Activity implements ScrollViewListener {

    private ObservableScrollView scrollView1 = null;
    private ObservableScrollView scrollView2 = null;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        scrollView1 = (ObservableScrollView) findViewById(R.id.scrollview1);
        scrollView1.setScrollViewListener(this);
        scrollView2 = (ObservableScrollView) findViewById(R.id.scrollview2);
        scrollView2.setScrollViewListener(this);
    }

    public void onScrollChanged(ObservableScrollView scrollView, int x, int y, int oldx, int oldy) {
        if(scrollView == scrollView1) {
            scrollView2.scrollTo(x, y);
        } else if(scrollView == scrollView2) {
            scrollView1.scrollTo(x, y);
        }
    }

}