Android 监听ScrollView的滑动

    有时候我们需要监听ScroView的滑动情况，比如滑动了多少距离，是否滑到布局的顶部或者底部。可惜的是SDK并没有相应的方法，不过倒是提供了一个 

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

   方法，显然这个方法是不能被外界调用的，因此就需要把它暴露出去，方便使用。解决方式就是写一个接口， 

package com.example.demo1;

public interface ScrollViewListener {

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

}

  然后重写ScrollView类，给它提供上面写的回调接口。 

package com.example.demo1;

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);
        }
    }

}

  注意在xml布局的时候，不要写错了包。 

<LinearLayout 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"
    android:orientation="horizontal"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context=".MainActivity" >

    <com.example.demo1.ObservableScrollView
        android:id="@+id/view1"
        android:layout_width="wrap_content"
        android:layout_height="match_parent" >

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

            <TextView
                android:layout_width="100dp"
                android:layout_height="100dp"
                android:text="试试1" />

            <TextView
                android:layout_width="100dp"
                android:layout_height="100dp"
                android:text="试试2" />

            <TextView
                android:layout_width="100dp"
                android:layout_height="100dp"
                android:text="试试3" />

            <TextView
                android:layout_width="100dp"
                android:layout_height="100dp"
                android:text="试试4" />

            <TextView
                android:layout_width="100dp"
                android:layout_height="100dp"
                android:text="试试5" />

            <TextView
                android:layout_width="100dp"
                android:layout_height="100dp"
                android:text="试试6" />
        </LinearLayout>
    </com.example.demo1.ObservableScrollView>

    <com.example.demo1.ObservableScrollView
        android:id="@+id/view2"
        android:layout_width="wrap_content"
        android:layout_height="match_parent" >

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

            <TextView
                android:layout_width="100dp"
                android:layout_height="100dp"
                android:text="试试1" />

            <TextView
                android:layout_width="100dp"
                android:layout_height="100dp"
                android:text="试试2" />

            <TextView
                android:layout_width="100dp"
                android:layout_height="100dp"
                android:text="试试3" />

            <TextView
                android:layout_width="100dp"
                android:layout_height="100dp"
                android:text="试试4" />

            <TextView
                android:layout_width="100dp"
                android:layout_height="100dp"
                android:text="试试5" />

            <TextView
                android:layout_width="100dp"
                android:layout_height="100dp"
                android:text="试试6" />
        </LinearLayout>
    </com.example.demo1.ObservableScrollView>

</LinearLayout>

  最后activity代码如下， 

package com.example.demo1;

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

public class MainActivity extends Activity implements ScrollViewListener {

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

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

        scrollView1 = (ObservableScrollView) findViewById(R.id.view1);
        scrollView1.setScrollViewListener(this);
        scrollView2 = (ObservableScrollView) findViewById(R.id.view2);
        scrollView2.setScrollViewListener(this);

    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

    @Override
    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);
        }
    }

}