Android 自定義View之Scroller處理滾動工具類詳解
阿新 • • 發佈：2019-01-25
public class ScrollerLayout extends ViewGroup {
/**
* 用於完成滾動操作的例項
*/
private Scroller mScroller;
/**
* 判定為拖動的最小移動畫素數
*/
private int mTouchSlop;
/**
* 手機按下時的螢幕座標
*/
private float mXDown;
/**
* 手機當時所處的螢幕座標
*/
private float mXMove;
/**
* 上次觸發ACTION_MOVE事件時的螢幕座標
*/
private float mXLastMove;
/**
* 介面可滾動的左邊界
*/
private int leftBorder;
/**
* 介面可滾動的右邊界
*/
private int rightBorder;
public ScrollerLayout(Context context, AttributeSet attrs) {
super(context, attrs);
// 第一步，建立Scroller的例項
mScroller = new Scroller(context);
ViewConfiguration configuration = ViewConfiguration.get(context);
// 獲取TouchSlop值
mTouchSlop = ViewConfigurationCompat.getScaledPagingTouchSlop(configuration);
}
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
int childCount = getChildCount();
for (int i = 0; i < childCount; i++) {
View childView = getChildAt(i);
// 為ScrollerLayout中的每一個子控制元件測量大小
measureChild(childView, widthMeasureSpec, heightMeasureSpec);
}
}
@Override
protected void onLayout(boolean changed, int l, int t, int r, int b) {
if (changed) {
int childCount = getChildCount();
for (int i = 0; i < childCount; i++) {
View childView = getChildAt(i);
// 為ScrollerLayout中的每一個子控制元件在水平方向上進行佈局
childView.layout(i * childView.getMeasuredWidth(), 0, (i + 1) * childView.getMeasuredWidth(), childView.getMeasuredHeight());
}
// 初始化左右邊界值
leftBorder = getChildAt(0).getLeft();
rightBorder = getChildAt(getChildCount() - 1).getRight();
}
}
@Override
public boolean onInterceptTouchEvent(MotionEvent ev) {
switch (ev.getAction()) {
case MotionEvent.ACTION_DOWN:
mXDown = ev.getRawX();
mXLastMove = mXDown;
break;
case MotionEvent.ACTION_MOVE:
mXMove = ev.getRawX();
float diff = Math.abs(mXMove - mXDown);
mXLastMove = mXMove;
// 當手指拖動值大於TouchSlop值時，認為應該進行滾動，攔截子控制元件的事件
if (diff > mTouchSlop) {
return true;
}
break;
}
return super.onInterceptTouchEvent(ev);
}
@Override
public boolean onTouchEvent(MotionEvent event) {
switch (event.getAction()) {
case MotionEvent.ACTION_MOVE:
mXMove = event.getRawX();
int scrolledX = (int) (mXLastMove - mXMove);
if (getScrollX() + scrolledX < leftBorder) {
scrollTo(leftBorder, 0);
return true;
} else if (getScrollX() + getWidth() + scrolledX > rightBorder) {
scrollTo(rightBorder - getWidth(), 0);
return true;
}
scrollBy(scrolledX, 0);
mXLastMove = mXMove;
break;
case MotionEvent.ACTION_UP:
// 當手指擡起時，根據當前的滾動值來判定應該滾動到哪個子控制元件的介面
int targetIndex = (getScrollX() + getWidth() / 2) / getWidth();
int dx = targetIndex * getWidth() - getScrollX();
// 第二步，呼叫startScroll()方法來初始化滾動資料並重新整理介面
mScroller.startScroll(getScrollX(), 0, dx, 0);
invalidate();
break;
}
return super.onTouchEvent(event);
}
@Override
public void computeScroll() {
// 第三步，重寫computeScroll()方法，並在其內部完成平滑滾動的邏輯
if (mScroller.computeScrollOffset()) {
scrollTo(mScroller.getCurrX(), mScroller.getCurrY());
invalidate();
}
}
}