看效果图:
手指可以滑动图片切换到一个图片，这种放到App的帮助页面是很合适的，然后也适合图片轮播图等等场合
我们来看一下Activity中怎么调用这个控件:
public class SnapToScreenActivity extends Activity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
requestWindowFeature(Window.FEATURE_NO_TITLE);
setContentView(R.layout.snap_to_screen);
int[] images = new int[]{R.drawable.help_01,R.drawable.help_02,R.drawable.help_03};
MyGroup myGroup = (MyGroup) findViewById(R.id.workspace);
for (int i = 0; i < 3; i++) {
final View item = getLayoutInflater().inflate(
R.layout.introduction_item_test, null);
myGroup.addView(item);
final ImageView imageView = (ImageView) item
.findViewById(R.id.introduction_image_view);
try {
imageView.setImageResource(images[i]);
} catch (OutOfMemoryError e) {
}
}
}
}
MyGroup这个类明显是一个ViewGroup,为了让这个viewGroup可以支持手指切换，我们要重写
onLayout,dispatchDraw,computeScroll,onMeasure,onInterceptTouchEvent,onTouchEvent这些方法
重点在于对手指的事件处理，下面我们来看代码，如何算一次正常的手指滑动:
@Override
public boolean onInterceptTouchEvent(MotionEvent ev) {
final int action = ev.getAction();
if ((action == MotionEvent.ACTION_MOVE)
&& (mTouchState != TOUCH_STATE_REST)) {
return true;
}
final float x = ev.getX();
switch (action) {
case MotionEvent.ACTION_MOVE:
final int xDiff = (int) Math.abs(x - mLastMotionX);
final int touchSlop = mTouchSlop;
boolean xMoved = xDiff > touchSlop;
if (xMoved) {
mTouchState = TOUCH_STATE_SCROLLING;
}
break;
case MotionEvent.ACTION_DOWN:
mLastMotionX = x;
mTouchState = mScroller.isFinished() ? TOUCH_STATE_REST
: TOUCH_STATE_SCROLLING;
break;
case MotionEvent.ACTION_CANCEL:
case MotionEvent.ACTION_UP:
mTouchState = TOUCH_STATE_REST;
break;
default:
break;
}
return mTouchState != TOUCH_STATE_REST;
}
@Override
public boolean onTouchEvent(MotionEvent ev) {
if (mVelocityTracker == null) {
mVelocityTracker = VelocityTracker.obtain();
}
mVelocityTracker.addMovement(ev);
int mScrollX = this.getScrollX();
final int action = ev.getAction();
final float x = ev.getX();
final float y = ev.getY();
switch (action) {
case MotionEvent.ACTION_DOWN:
mOriMotionX = x;
mLastMotionX = x;
if (!mScroller.isFinished()) {
mScroller.abortAnimation();
}
mOriMotionX = x;
mLastMotionX = x;
mLastDownX = x;
return true;
case MotionEvent.ACTION_MOVE:
System.out.println("====action move mScrollX="+mScrollX);
final int buffer = getWidth() / 2;
int deltaX = (int) (mLastMotionX - x);
mLastMotionX = x;
System.out.println("=====deltaX="+deltaX);
if (deltaX < 0) {
scrollBy(Math.max(-mScrollX - buffer, deltaX), 0);
}else{
int availableToScroll = 0;
if (getChildCount() > 0) {
System.out.println("====rihgt="+(getChildAt(
getChildCount() - 1).getRight())+"avail="+(getChildAt(
getChildCount() - 1).getRight()- mScrollX - getWidth()
));
availableToScroll = getChildAt(
getChildCount() - 1).getRight()
- mScrollX - getWidth();
scrollBy(Math.min(availableToScroll + buffer, deltaX), 0);
}
}
return true;
case MotionEvent.ACTION_UP:
final VelocityTracker velocityTracker = mVelocityTracker;
velocityTracker.computeCurrentVelocity(DEFAULT_VALUE,
mMaximumVelocity);
int velocityX = (int) velocityTracker.getXVelocity();
if (velocityX > SNAP_VELOCITY && mCurrentScreen > 0) {
snapToScreen(mCurrentScreen - 1);
} else if (velocityX < -SNAP_VELOCITY
&& mCurrentScreen < getChildCount() - 1) {
// move right
snapToScreen(mCurrentScreen + 1);
} else {
snapToDestination(mLastMotionX < mOriMotionX);
}
if (mVelocityTracker != null) {
mVelocityTracker.recycle();
mVelocityTracker = null;
}
mTouchState = TOUCH_STATE_REST;
if (Math.abs(mLastDownX - x) > 10) {
return true;
}
return false;
case MotionEvent.ACTION_CANCEL:
mTouchState = TOUCH_STATE_REST;
return false;
default:
break;
}
return true;
}onLayout是相对简单的，只是把子view布局一下就行
@Override
protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
int paddingleft = 0;
int paddingTop = 0;
int childLeft = paddingleft;
final int count = getChildCount();
for (int i = 0; i < count; i++) {
final View child = getChildAt(i);
if (child.getVisibility() != View.GONE) {
final int childWidth = child.getMeasuredWidth();
final int childHeight = child.getMeasuredHeight() ;
child.layout(childLeft, paddingTop, childLeft + childWidth,
childHeight + paddingTop);
childLeft += child.getMeasuredWidth();
}
}
}重点在于
childLeft += child.getMeasuredWidth();
这一句，使得每个字view都并排排列
然后使用dispatchDraw()绘制每个view
@Override
protected void dispatchDraw(Canvas canvas) {
int childCount = getChildCount();
if (childCount == 0) {
return;
}
boolean restore = false;
int restoreCount = 0;
final long drawingTime = getDrawingTime();
final float scrollPos = (float) getScrollX() / getWidth();
final int leftScreen = (int) scrollPos;
final int rightScreen = leftScreen + 1;
if (leftScreen >= 0 && leftScreen < childCount) {
drawChild(canvas, getChildAt(leftScreen), drawingTime);
}
if (rightScreen < getChildCount()) {
drawChild(canvas, getChildAt(rightScreen), drawingTime);
}
if (restore) {
canvas.restoreToCount(restoreCount);
}
}这个类的完整代码我也贴出来:
public class MyGroup extends ViewGroup{
private Scroller mScroller;
private float mOriMotionX;
private float mLastMotionX;
private VelocityTracker mVelocityTracker;
private int mTouchState = TOUCH_STATE_REST;
private static final int TOUCH_STATE_REST = 0;
private int mTouchSlop;
private int mMaximumVelocity;
private static final int TOUCH_STATE_SCROLLING = 1;
private float mLastDownX;
private static final int DEFAULT_VALUE = 1000;
private int mNextScreen = -1;
private static final int SNAP_VELOCITY = 700;
private int mCurrentScreen;
public MyGroup(Context context, AttributeSet attrs) {
super(context, attrs);
initWorkspace();
}
private void initWorkspace() {
mScroller = new Scroller(getContext());
setCurrentScreen(0);
final ViewConfiguration configuration = ViewConfiguration
.get(getContext());
mTouchSlop = configuration.getScaledTouchSlop();
mMaximumVelocity = configuration.getScaledMaximumFlingVelocity();
}
@Override
protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
int paddingleft = 0;
int paddingTop = 0;
int childLeft = paddingleft;
final int count = getChildCount();
for (int i = 0; i < count; i++) {
final View child = getChildAt(i);
if (child.getVisibility() != View.GONE) {
final int childWidth = child.getMeasuredWidth();
final int childHeight = child.getMeasuredHeight() ;
child.layout(childLeft, paddingTop, childLeft + childWidth,
childHeight + paddingTop);
childLeft += child.getMeasuredWidth();
}
}
}
@Override
protected void dispatchDraw(Canvas canvas) {
int childCount = getChildCount();
if (childCount == 0) {
return;
}
boolean restore = false;
int restoreCount = 0;
final long drawingTime = getDrawingTime();
final float scrollPos = (float) getScrollX() / getWidth();
final int leftScreen = (int) scrollPos;
final int rightScreen = leftScreen + 1;
if (leftScreen >= 0 && leftScreen < childCount) {
drawChild(canvas, getChildAt(leftScreen), drawingTime);
}
if (rightScreen < getChildCount()) {
drawChild(canvas, getChildAt(rightScreen), drawingTime);
}
if (restore) {
canvas.restoreToCount(restoreCount);
}
}
@Override
public void computeScroll() {
if (mScroller.computeScrollOffset()) {
scrollTo(mScroller.getCurrX(), mScroller.getCurrY());
postInvalidate();
} else if (mNextScreen != -1) {
setCurrentScreen(Math.max(0,
Math.min(mNextScreen, getChildCount() - 1)));
mNextScreen = -1;
// if (mListener != null) {
// mListener.onViewChanged(mCurrentScreen);
// }
}
}
void setCurrentScreen(int index) {
mCurrentScreen = index;
resetVisibilityForChildren();
}
private void resetVisibilityForChildren() {
int count = getChildCount();
for (int i = 0; i < count; i++) {
View child = getChildAt(i);
if (Math.abs(mCurrentScreen - i) <= 0) {
child.setVisibility(View.VISIBLE);
} else {
child.setVisibility(View.INVISIBLE);
}
}
}
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
final int width = MeasureSpec.getSize(widthMeasureSpec);
final int count = getChildCount();
for (int i = 0; i < count; i++) {
getChildAt(i).measure(widthMeasureSpec, heightMeasureSpec);
}
}
@Override
public boolean onInterceptTouchEvent(MotionEvent ev) {
final int action = ev.getAction();
if ((action == MotionEvent.ACTION_MOVE)
&& (mTouchState != TOUCH_STATE_REST)) {
return true;
}
final float x = ev.getX();
switch (action) {
case MotionEvent.ACTION_MOVE:
final int xDiff = (int) Math.abs(x - mLastMotionX);
final int touchSlop = mTouchSlop;
boolean xMoved = xDiff > touchSlop;
if (xMoved) {
mTouchState = TOUCH_STATE_SCROLLING;
}
break;
case MotionEvent.ACTION_DOWN:
mLastMotionX = x;
mTouchState = mScroller.isFinished() ? TOUCH_STATE_REST
: TOUCH_STATE_SCROLLING;
break;
case MotionEvent.ACTION_CANCEL:
case MotionEvent.ACTION_UP:
mTouchState = TOUCH_STATE_REST;
break;
default:
break;
}
return mTouchState != TOUCH_STATE_REST;
}
@Override
public boolean onTouchEvent(MotionEvent ev) {
if (mVelocityTracker == null) {
mVelocityTracker = VelocityTracker.obtain();
}
mVelocityTracker.addMovement(ev);
int mScrollX = this.getScrollX();
final int action = ev.getAction();
final float x = ev.getX();
final float y = ev.getY();
switch (action) {
case MotionEvent.ACTION_DOWN:
mOriMotionX = x;
mLastMotionX = x;
if (!mScroller.isFinished()) {
mScroller.abortAnimation();
}
mOriMotionX = x;
mLastMotionX = x;
mLastDownX = x;
return true;
case MotionEvent.ACTION_MOVE:
System.out.println("====action move mScrollX="+mScrollX);
final int buffer = getWidth() / 2;
int deltaX = (int) (mLastMotionX - x);
mLastMotionX = x;
System.out.println("=====deltaX="+deltaX);
if (deltaX < 0) {
scrollBy(Math.max(-mScrollX - buffer, deltaX), 0);
}else{
int availableToScroll = 0;
if (getChildCount() > 0) {
System.out.println("====rihgt="+(getChildAt(
getChildCount() - 1).getRight())+"avail="+(getChildAt(
getChildCount() - 1).getRight()- mScrollX - getWidth()
));
availableToScroll = getChildAt(
getChildCount() - 1).getRight()
- mScrollX - getWidth();
scrollBy(Math.min(availableToScroll + buffer, deltaX), 0);
}
}
return true;
case MotionEvent.ACTION_UP:
final VelocityTracker velocityTracker = mVelocityTracker;
velocityTracker.computeCurrentVelocity(DEFAULT_VALUE,
mMaximumVelocity);
int velocityX = (int) velocityTracker.getXVelocity();
if (velocityX > SNAP_VELOCITY && mCurrentScreen > 0) {
snapToScreen(mCurrentScreen - 1);
} else if (velocityX < -SNAP_VELOCITY
&& mCurrentScreen < getChildCount() - 1) {
// move right
snapToScreen(mCurrentScreen + 1);
} else {
snapToDestination(mLastMotionX < mOriMotionX);
}
if (mVelocityTracker != null) {
mVelocityTracker.recycle();
mVelocityTracker = null;
}
mTouchState = TOUCH_STATE_REST;
if (Math.abs(mLastDownX - x) > 10) {
return true;
}
return false;
case MotionEvent.ACTION_CANCEL:
mTouchState = TOUCH_STATE_REST;
return false;
default:
break;
}
return true;
}
public void snapToDestination(boolean forward) {
final int screenWidth = getWidth();
int scrollX = getScrollX();
if (forward) {
scrollX += screenWidth - screenWidth / 3;
} else {
scrollX += screenWidth / 3;
}
System.out.println("======screenWidth="+screenWidth+"scrollX / screenWidth="+(scrollX / screenWidth));
snapToScreen(scrollX / screenWidth);
}
public void snapToScreen(int whichScreen) {
whichScreen = Math.max(0, Math.min(whichScreen, getChildCount() - 1));
boolean changingScreens = whichScreen != mCurrentScreen;
mNextScreen = whichScreen;
int mScrollX = this.getScrollX();
final int newX = whichScreen * getWidth();
final int delta = newX - mScrollX;
System.out.println("====snapToScreen delta="+delta);
mScroller.startScroll(mScrollX, 0, delta, 0, Math.abs(delta) * 2);
invalidate();
}
}
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