Android Open Source - android-training-tutorial Swipe Dismiss Touch Listener

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The source code is released under:

MIT License

Java Source Code

package com.flavienlaurent.vdh.listener;
// w w  w.  j  a v a2s.  co m
import android.animation.Animator;
import android.animation.AnimatorListenerAdapter;
import android.animation.ValueAnimator;
import android.app.ListActivity;
import android.app.ListFragment;
import android.view.MotionEvent;
import android.view.VelocityTracker;
import android.view.View;
import android.view.ViewConfiguration;
import android.view.ViewGroup;
import android.widget.AdapterView;
import android.widget.ListView;

/**
 * A {@link View.OnTouchListener} that makes any {@link View} dismissable when
 * the user swipes (drags her finger) horizontally across the view.
 * 
 * <p>
 * <em>For {@link ListView} list items that don't manage their own touch events
 * (i.e. you're using
 * {@link ListView#setOnItemClickListener(AdapterView.OnItemClickListener)}
 * or an equivalent listener on {@link ListActivity} or
 * {@link ListFragment}, use {@link SwipeDismissListViewTouchListener} instead.</em>
 * </p>
 * 
 * <p>
 * Example usage:
 * </p>
 * 
 * <pre>
 * view.setOnTouchListener(new SwipeDismissTouchListener(view, null, // Optional
 *                                   // token/cookie
 *                                   // object
 *     new SwipeDismissTouchListener.OnDismissCallback() {
 *       public void onDismiss(View view, Object token) {
 *         parent.removeView(view);
 *       }
 *     }));
 * </pre>
 * 
 * <p>
 * This class Requires API level 12 or later due to use of
 * {@link android.view.ViewPropertyAnimator}.
 * </p>
 * 
 * @see SwipeDismissListViewTouchListener
 */
public class SwipeDismissTouchListener implements View.OnTouchListener {
  // Cached ViewConfiguration and system-wide constant values
  private int mSlop;
  private int mMinFlingVelocity;
  private int mMaxFlingVelocity;
  private long mAnimationTime;

  // Fixed properties
  private View mView;
  private DismissCallbacks mCallbacks;
  private int mViewWidth = 1; // 1 and not 0 to prevent dividing by zero

  // Transient properties
  private float mDownX;
  private float mDownY;
  private boolean mSwiping;
  private int mSwipingSlop;
  private Object mToken;
  private VelocityTracker mVelocityTracker;
  private float mTranslationX;

  /**
   * The callback interface used by {@link SwipeDismissTouchListener} to
   * inform its client about a successful dismissal of the view for which it
   * was created.
   */
  public interface DismissCallbacks {
    /**
     * Called to determine whether the view can be dismissed.
     */
    boolean canDismiss(Object token);

    /**
     * Called when the user has indicated they she would like to dismiss the
     * view.
     * 
     * @param view
     *            The originating {@link View} to be dismissed.
     * @param token
     *            The optional token passed to this object's constructor.
     */
    void onDismiss(View view, Object token);
  }

  /**
   * Constructs a new swipe-to-dismiss touch listener for the given view.
   * 
   * @param view
   *            The view to make dismissable.
   * @param token
   *            An optional token/cookie object to be passed through to the
   *            callback.
   * @param callbacks
   *            The callback to trigger when the user has indicated that she
   *            would like to dismiss this view.
   */
  public SwipeDismissTouchListener(View view, Object token,
      DismissCallbacks callbacks) {
    ViewConfiguration vc = ViewConfiguration.get(view.getContext());
    mSlop = vc.getScaledTouchSlop();
    mMinFlingVelocity = vc.getScaledMinimumFlingVelocity() * 16;
    mMaxFlingVelocity = vc.getScaledMaximumFlingVelocity();
    mAnimationTime = view.getContext().getResources()
        .getInteger(android.R.integer.config_shortAnimTime);
    mView = view;
    mToken = token;
    mCallbacks = callbacks;
  }

  @Override
  public boolean onTouch(View view, MotionEvent motionEvent) {
    // offset because the view is translated during swipe
    motionEvent.offsetLocation(mTranslationX, 0);

    if (mViewWidth < 2) {
      mViewWidth = mView.getWidth();
    }

    switch (motionEvent.getActionMasked()) {
    case MotionEvent.ACTION_DOWN: {
      // TODO: ensure this is a finger, and set a flag
      mDownX = motionEvent.getRawX();
      mDownY = motionEvent.getRawY();
      if (mCallbacks.canDismiss(mToken)) {
        mVelocityTracker = VelocityTracker.obtain();
        mVelocityTracker.addMovement(motionEvent);
      }
      return false;
    }

    case MotionEvent.ACTION_UP: {
      if (mVelocityTracker == null) {
        break;
      }

      float deltaX = motionEvent.getRawX() - mDownX;
      mVelocityTracker.addMovement(motionEvent);
      mVelocityTracker.computeCurrentVelocity(1000);
      float velocityX = mVelocityTracker.getXVelocity();
      float absVelocityX = Math.abs(velocityX);
      float absVelocityY = Math.abs(mVelocityTracker.getYVelocity());
      boolean dismiss = false;
      boolean dismissRight = false;
      if (Math.abs(deltaX) > mViewWidth / 2 && mSwiping) {
        dismiss = true;
        dismissRight = deltaX > 0;
      } else if (mMinFlingVelocity <= absVelocityX
          && absVelocityX <= mMaxFlingVelocity
          && absVelocityY < absVelocityX
          && absVelocityY < absVelocityX && mSwiping) {
        // dismiss only if flinging in the same direction as dragging
        dismiss = (velocityX < 0) == (deltaX < 0);
        dismissRight = mVelocityTracker.getXVelocity() > 0;
      }
      if (dismiss) {
        // dismiss
        mView.animate()
            .translationX(dismissRight ? mViewWidth : -mViewWidth)
            .alpha(0).setDuration(mAnimationTime)
            .setListener(new AnimatorListenerAdapter() {
              @Override
              public void onAnimationEnd(Animator animation) {
                performDismiss();
              }
            });
      } else if (mSwiping) {
        // cancel
        mView.animate().translationX(0).alpha(1)
            .setDuration(mAnimationTime).setListener(null);
      }
      mVelocityTracker.recycle();
      mVelocityTracker = null;
      mTranslationX = 0;
      mDownX = 0;
      mDownY = 0;
      mSwiping = false;
      break;
    }

    case MotionEvent.ACTION_CANCEL: {
      if (mVelocityTracker == null) {
        break;
      }

      mView.animate().translationX(0).alpha(1)
          .setDuration(mAnimationTime).setListener(null);
      mVelocityTracker.recycle();
      mVelocityTracker = null;
      mTranslationX = 0;
      mDownX = 0;
      mDownY = 0;
      mSwiping = false;
      break;
    }

    case MotionEvent.ACTION_MOVE: {
      if (mVelocityTracker == null) {
        break;
      }

      mVelocityTracker.addMovement(motionEvent);
      float deltaX = motionEvent.getRawX() - mDownX;
      float deltaY = motionEvent.getRawY() - mDownY;
      if (Math.abs(deltaX) > mSlop
          && Math.abs(deltaY) < Math.abs(deltaX) / 2) {
        mSwiping = true;
        mSwipingSlop = (deltaX > 0 ? mSlop : -mSlop);
        mView.getParent().requestDisallowInterceptTouchEvent(true);

        // Cancel listview's touch
        MotionEvent cancelEvent = MotionEvent.obtain(motionEvent);
        cancelEvent
            .setAction(MotionEvent.ACTION_CANCEL
                | (motionEvent.getActionIndex() << MotionEvent.ACTION_POINTER_INDEX_SHIFT));
        mView.onTouchEvent(cancelEvent);
        cancelEvent.recycle();
      }

      if (mSwiping) {
        mTranslationX = deltaX;
        mView.setTranslationX(deltaX - mSwipingSlop);
        // TODO: use an ease-out interpolator or such
        mView.setAlpha(Math.max(0f,
            Math.min(1f, 1f - 2f * Math.abs(deltaX) / mViewWidth)));
        return true;
      }
      break;
    }
    }
    return false;
  }

  private void performDismiss() {
    // Animate the dismissed view to zero-height and then fire the dismiss
    // callback.
    // This triggers layout on each animation frame; in the future we may
    // want to do something
    // smarter and more performant.

    final ViewGroup.LayoutParams lp = mView.getLayoutParams();
    final int originalHeight = mView.getHeight();

    ValueAnimator animator = ValueAnimator.ofInt(originalHeight, 1)
        .setDuration(mAnimationTime);

    animator.addListener(new AnimatorListenerAdapter() {
      @Override
      public void onAnimationEnd(Animator animation) {
        mCallbacks.onDismiss(mView, mToken);
        // Reset view presentation
        mView.setAlpha(1f);
        mView.setTranslationX(0);
        lp.height = originalHeight;
        mView.setLayoutParams(lp);
      }
    });

    animator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
      @Override
      public void onAnimationUpdate(ValueAnimator valueAnimator) {
        lp.height = (Integer) valueAnimator.getAnimatedValue();
        mView.setLayoutParams(lp);
      }
    });

    animator.start();
  }
}

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