[Android] ScrollView滾動到底部和頂部的檢測

1. 源起

    很多分頁載入的組件都是繼承自ScrollView，分頁要檢查是否滾動到底部，下拉重新整理需要檢測是否滾動到頂部。

2. 代碼

<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=".MainActivity" >    <ScrollView        android:id="@+id/scroll_view"        android:layout_width="match_parent"        android:layout_height="match_parent"        android:scrollbars="vertical" >        <LinearLayout            android:layout_width="match_parent"            android:layout_height="wrap_content"            android:background="@android:color/darker_gray"            android:orientation="vertical" >            <TextView                android:layout_width="wrap_content"                android:layout_height="2000dip"                android:text="text" />        </LinearLayout>    </ScrollView></RelativeLayout>

public class MainActivity extends Activity {    @Override    protected void onCreate(Bundle savedInstanceState) {    super.onCreate(savedInstanceState);    setContentView(R.layout.activity_main);    final ScrollView view = (ScrollView) findViewById(R.id.scroll_view);    view.setOnTouchListener(new OnTouchListener() {        @Override        public boolean onTouch(View v, MotionEvent event) {            switch (event.getAction()) {            case MotionEvent.ACTION_DOWN:                break;            case MotionEvent.ACTION_MOVE:                if (v.getScrollY() <= 0) {                    Log.d("scroll view", "top");                } else if (view.getChildAt(0).getMeasuredHeight() <= v.getHeight() + v.getScrollY()) {                    Log.d("scroll view", "bottom");                    Log.d("scroll view", "view.getMeasuredHeight() = " + view.getMeasuredHeight()                        + ", v.getHeight() = " + v.getHeight()                        + ", v.getScrollY() = " + v.getScrollY()                        + ", view.getChildAt(0).getMeasuredHeight() = " + view.getChildAt(0).getMeasuredHeight());                }                break;            default:                break;            }            return false;} });    }}

3. 說明

    檢測滾動的時機有很多，這裡是在ScrollView外面檢測，使用onTouch的MotionEvent.ACTION_MOVE。如果是繼承ScrollView，可以在其他回調的時候檢測。

    v.getScrollY()表示scrollview的上面滾出去的長度。v.getHeight()表示scrollview本身看上去的高度。view.getChildAt(0).getMeasuredHeight()是內容的高度。這裡不能用view.getMeasureHeight()。

    view.getMeasuredHeight() = 1038

    v.getHeight() = 1038

    v.getScrollY() = 2962

    view.getChildAt(0).getMeasuredHeight() = 4000