我已经实现了 Android Note Pad 示例代码中的编辑器代码。现在我想添加垂直滚动文本行的功能。我想要完成的一个例子是 Andorid 中选项行的快速滚动
我在谷歌上搜索了滚动器和投掷的示例，但找不到任何适合我需要的东西。我还没有找到任何与我想做的事情有一点距离的东西。
我通过鲜血、汗水和泪水找到了我的问题的答案。我将其发布在这里希望对其他人有所帮助。以下方法位于 Android Note Pad 示例代码的 LinedEditText 类中。
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public void InitScroller(Context context) {
mScroller = new Scroller(context); // Get a scroller object
mScrollY = 0 ; // Set beginning of program as top of screen.
mMinScroll = getLineHeight ()/2; // Set minimum scroll distance
mFlingV = 750; // Minimum fling velocity
}
@Override
public boolean onTouchEvent(MotionEvent event) {
super.onTouchEvent(event);
if (mVelocityTracker == null) { // If we do not have velocity tracker
mVelocityTracker = VelocityTracker.obtain(); // then get one
}
mVelocityTracker.addMovement(event); // add this movement to it
final int action = event.getAction(); // Get action type
final float y = event.getY(); // Get the displacement for the action
switch (action) {
case MotionEvent.ACTION_DOWN: // User has touched screen
if (!mScroller.isFinished()) { // If scrolling, then stop now
mScroller.abortAnimation();
}
mLastMotionY = y; // Save start (or end) of motion
mScrollY = this.getScrollY(); // Save where we ended up
mText.setCursorVisible (true);
didMove = false;
break;
case MotionEvent.ACTION_MOVE: // The user finger is on the move
didMove = true;
final int deltaY = (int) (mLastMotionY - y); // Calculate distance moved since last report
mLastMotionY = y; // Save the start of this motion
if (deltaY < 0) { // If user is moving finger up screen
if (mScrollY > 0) { // and we are not at top of text
int m = mScrollY - mMinScroll; // Do not go beyond top of text
if (m < 0){
m = mScrollY;
}else m = mMinScroll;
scrollBy(0, -m); // Scroll the text up
}
} else
if (deltaY > 0) { // The user finger is moving up
int max = getLineCount() * getLineHeight () - sHeight; // Set max up value
if (mScrollY < max-mMinScroll){
scrollBy(0, mMinScroll); // Scroll up
}
}
postInvalidate();
break;
case MotionEvent.ACTION_UP: // User finger lifted up
final VelocityTracker velocityTracker = mVelocityTracker; // Find out how fast the finger was moving
velocityTracker.computeCurrentVelocity(mFlingV);
int velocityY = (int) velocityTracker.getYVelocity();
if (Math.abs(velocityY) > mFlingV){ // if the velocity exceeds threshold
int maxY = getLineCount() * getLineHeight () - sHeight; // calculate maximum Y movement
mScroller.fling(0, mScrollY, 0, -velocityY, 0, 0, 0, maxY); // Do the filng
}else{
if (mVelocityTracker != null) { // If the velocity less than threshold
mVelocityTracker.recycle(); // recycle the tracker
mVelocityTracker = null;
}
}
break;
}
mScrollY = this.getScrollY(); // Save where we ended up
return true ; // Tell caller we handled the move event
}
public void computeScroll() { // Called while flinging to execute a fling step
if (mScroller.computeScrollOffset()) {
mScrollY = mScroller.getCurrY(); // Get where we should scroll to
scrollTo(0, mScrollY); // and do it
postInvalidate(); // the redraw the sreem
}
}
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