先上源码:
package net.oschina.app.widget;
import android.annotation.SuppressLint;
import android.content.Context;
import android.graphics.Rect;
import android.util.AttributeSet;
import android.util.Log;
import android.view.MotionEvent;
import android.view.View;
import android.view.animation.TranslateAnimation;
import android.widget.ScrollView;
/**
* 可以拖动的ScrollView
*
*/
public class CustomerScrollView extends ScrollView {
private static final String TAG = "CustomerScrollView";
private static final int size = 4;
private View inner;
private float y;
private Rect normal = new Rect();
public CustomerScrollView(Context context) {
super(context);
}
public CustomerScrollView(Context context, AttributeSet attrs) {
super(context, attrs);
}
@Override
protected void onFinishInflate() {
if (getChildCount() > 0) {
inner = getChildAt(0);
}
}
@SuppressLint("ClickableViewAccessibility")
@Override
public boolean onTouchEvent(MotionEvent ev) {
if (inner == null) {
return super.onTouchEvent(ev);
} else {
commOnTouchEvent(ev);
}
return super.onTouchEvent(ev);
}
public void commOnTouchEvent(MotionEvent ev) {
int action = ev.getAction();
switch (action) {
case MotionEvent.ACTION_DOWN:
y = ev.getY();
break;
case MotionEvent.ACTION_UP:
if (isNeedAnimation()) {
// Log.v("mlguitar", "will up and animation");
animation();
}
break;
case MotionEvent.ACTION_MOVE:
final float preY = y;
float nowY = ev.getY();
/**
* size=4 表示 拖动的距离为屏幕的高度的1/4
*/
int deltaY = (int) (preY - nowY) / size;
Log.i(TAG, "commOnTouchEvent: deltay="+ deltaY +"preY" + preY +"nowY" + nowY );
// 滚动
// scrollBy(0, deltaY);
y = nowY;
if (isNeedMove()) {
Log.i(TAG, "commOnTouchEvent: normal.isEmpty:" + normal.isEmpty());
if (normal.isEmpty()) {
Log.i(TAG, "commOnTouchEvent: inner:" + inner.getLeft() + "," + inner.getTop() + "," + inner.getRight() + "," + inner.getBottom());
normal.set(inner.getLeft(), inner.getTop(),
inner.getRight(), inner.getBottom());
return;
}
int yy = inner.getTop() - deltaY;
Log.i(TAG, "commOnTouchEvent: new layout:" + inner.getLeft() + "," + yy + "," + inner.getRight() + "," + (inner.getBottom() - deltaY));
// 移动布局
inner.layout(inner.getLeft(), yy, inner.getRight(),
inner.getBottom() - deltaY);
}
break;
default:
break;
}
}
public void animation() {
TranslateAnimation ta = new TranslateAnimation(0, 0, inner.getTop(),
normal.top);
ta.setDuration(200);
Log.i(TAG, "animation start " + "(0,0," + inner.getTop() +"," + normal.top + ")");
inner.startAnimation(ta);
inner.layout(normal.left, normal.top, normal.right, normal.bottom);
normal.setEmpty();
}
public boolean isNeedAnimation() {
Log.i(TAG, "isNeedAnimation: " + !normal.isEmpty());
return !normal.isEmpty();
}
public boolean isNeedMove() {
int offset = inner.getMeasuredHeight() - getHeight();
int scrollY = getScrollY();
Log.i(TAG, "isNeedMove: " + "scrollY=" + scrollY + "offset=" + offset);
if (scrollY == 0 || scrollY == offset) {
return true;
}
return false;
}
}
-
先看isNeedMove()函数:
- int offset = inner.getMeasuredHeight() - getHeight();
前者一般与后者相等,只有当view超出屏幕后前者才会比后者大,getMeasuredHeight() 等于 getHeight()加上屏幕之外没有显示的大小。
- int scrollY = getScrollY();
看下官方对这个函数的介绍:The top edge of the displayed part of your view, in pixels. 返回的是view的顶端超过屏幕部分的大小。
因此,这个函数的判断条件其实就是view在屏幕最上面或者最下面这两种情况才需要移动。
- 再看移动事件(commOnTouchEvent):
- 点击获取初始位置,抬起判断是否需要移动,主要看一下移动这个事件(MotionEvent.ACTION_MOVE)。
- 首先根据移动的Y和初始的Y得到移动的距离:int deltaY = (int) (preY - nowY) / size;
- 判断是否需要移动。如果需要,第一次用normal这个变量来记录原始的view范围,然后用inner.layout(inner.getLeft(), yy, inner.getRight(),
inner.getBottom() - deltaY);来移动布局。就是根据先前得到的移动距离来改变view的上下显示范围。
- 最后就是退回动画:TranslateAnimation ta = new TranslateAnimation(0, 0, inner.getTop(),
normal.top);就是简单的由现在的Y变化到记录的原始的Y。