Android SwipeToDismiss：左滑/右滑删除ListView条目Item

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《Android SwipeToDismiss：左右滑动删除ListView条目Item》

Android的SwipeToDismiss是github上一个第三方开源框架（github上的项目链接地址：https://github.com/romannurik/Android-SwipeToDismiss ）。该开源项目旨在：使得一个ListView的item在用户的手指在屏幕上左滑或者右滑时候，删除当前的这个ListView Item。

此种特效在新版的Android中应用不少。比方在Android 5.0及以上版本号中，通知栏下拉菜单中的条目。就是这样的操作效果，用户把通知栏下拉出来。手指轻触某一项。左滑或者右滑。删除（清除）此项。

在  https://github.com/romannurik/Android-SwipeToDismiss 上下载到到库文件有两个（此说是基于截止2015年7月27日的版本号，兴许版本号或许会有所不同）：SwipeDismissListViewTouchListener.java 和 SwipeDismissTouchListener.java
。假设仅仅是打算简单的仅仅是支持一个ListView列表中item左滑/右滑删除，那么仅仅仅仅导入SwipeDismissListViewTouchListener.java这一个库文件就可以。

如今就给出一个简单样例，说明怎样改造一个标准ListView。使其支持左右滑动某个item然后删除之。

測试用的MainActivity.java :

package zhangphil.listview;

import java.util.ArrayList;

import android.app.ListActivity;
import android.os.Bundle;
import android.util.Log;
import android.widget.ArrayAdapter;
import android.widget.ListView;

public class MainActivity extends ListActivity {

	private ArrayAdapter<String> adapter = null;
	private ArrayList<String> items = null;

	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);

		ListView listView = this.getListView();

		// 測试数据集。

items = new ArrayList<String>();
		for (int i = 0; i < 50; i++) {
			items.add("数据:" + i);
		}

		adapter = new ArrayAdapter<String>(this,
				android.R.layout.simple_list_item_1, items);
		listView.setAdapter(adapter);

		// 将ListView传递过来。

SwipeDismissListViewTouchListener touchListener = new SwipeDismissListViewTouchListener(
				listView,
				new SwipeDismissListViewTouchListener.DismissCallbacks() {

					@Override
					public boolean canDismiss(int position) {
						return true;
					}

					// 此处将运行删除。记得要notifyDataSetChanged()。
					@Override
					public void onDismiss(ListView listView,
							int[] reverseSortedPositions) {
						for (int pos : reverseSortedPositions) {
							items.remove(pos);
							Log.i(this.getClass().getName(), "删除:" + pos);
						}

						adapter.notifyDataSetChanged();
					}
				});

		listView.setOnTouchListener(touchListener);
	}
}

须要的库文件 SwipeDismissListViewTouchListener.java ：

/*
 * Copyright 2013 Google Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package zhangphil.listview;

import android.animation.Animator;
import android.animation.AnimatorListenerAdapter;
import android.animation.ValueAnimator;
import android.graphics.Rect;
import android.os.SystemClock;
import android.view.MotionEvent;
import android.view.VelocityTracker;
import android.view.View;
import android.view.ViewConfiguration;
import android.view.ViewGroup;
import android.view.ViewPropertyAnimator;
import android.widget.AbsListView;
import android.widget.ListView;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

/**
 * A {@link View.OnTouchListener} that makes the list items in a
 * {@link ListView} dismissable. {@link ListView} is given special treatment
 * because by default it handles touches for its list items... i.e. it‘s in
 * charge of drawing the pressed state (the list selector), handling list item
 * clicks, etc.
 *
 * <p>
 * After creating the listener, the caller should also call
 * {@link ListView#setOnScrollListener(AbsListView.OnScrollListener)}, passing
 * in the scroll listener returned by {@link #makeScrollListener()}. If a scroll
 * listener is already assigned, the caller should still pass scroll changes
 * through to this listener. This will ensure that this
 * {@link SwipeDismissListViewTouchListener} is paused during list view
 * scrolling.
 * </p>
 *
 * <p>
 * Example usage:
 * </p>
 *
 * <pre>
 * SwipeDismissListViewTouchListener touchListener = new SwipeDismissListViewTouchListener(
 * 		listView, new SwipeDismissListViewTouchListener.OnDismissCallback() {
 * 			public void onDismiss(ListView listView,
 * 					int[] reverseSortedPositions) {
 * 				for (int position : reverseSortedPositions) {
 * 					adapter.remove(adapter.getItem(position));
 * 				}
 * 				adapter.notifyDataSetChanged();
 * 			}
 * 		});
 * listView.setOnTouchListener(touchListener);
 * listView.setOnScrollListener(touchListener.makeScrollListener());
 * </pre>
 *
 * <p>
 * This class Requires API level 12 or later due to use of
 * {@link ViewPropertyAnimator}.
 * </p>
 *
 * <p>
 * For a generalized {@link View.OnTouchListener} that makes any view
 * dismissable, see {@link SwipeDismissTouchListener}.
 * </p>
 *
 * @see SwipeDismissTouchListener
 */
public class SwipeDismissListViewTouchListener 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 ListView mListView;
	private DismissCallbacks mCallbacks;
	private int mViewWidth = 1; // 1 and not 0 to prevent dividing by zero

	// Transient properties
	private List<PendingDismissData> mPendingDismisses = new ArrayList<PendingDismissData>();
	private int mDismissAnimationRefCount = 0;
	private float mDownX;
	private float mDownY;
	private boolean mSwiping;
	private int mSwipingSlop;
	private VelocityTracker mVelocityTracker;
	private int mDownPosition;
	private View mDownView;
	private boolean mPaused;

	/**
	 * The callback interface used by {@link SwipeDismissListViewTouchListener}
	 * to inform its client about a successful dismissal of one or more list
	 * item positions.
	 */
	public interface DismissCallbacks {
		/**
		 * Called to determine whether the given position can be dismissed.
		 */
		boolean canDismiss(int position);

		/**
		 * Called when the user has indicated they she would like to dismiss one
		 * or more list item positions.
		 *
		 * @param listView
		 *            The originating {@link ListView}.
		 * @param reverseSortedPositions
		 *            An array of positions to dismiss, sorted in descending
		 *            order for convenience.
		 */
		void onDismiss(ListView listView, int[] reverseSortedPositions);
	}

	/**
	 * Constructs a new swipe-to-dismiss touch listener for the given list view.
	 *
	 * @param listView
	 *            The list view whose items should be dismissable.
	 * @param callbacks
	 *            The callback to trigger when the user has indicated that she
	 *            would like to dismiss one or more list items.
	 */
	public SwipeDismissListViewTouchListener(ListView listView,
			DismissCallbacks callbacks) {
		ViewConfiguration vc = ViewConfiguration.get(listView.getContext());
		mSlop = vc.getScaledTouchSlop();
		mMinFlingVelocity = vc.getScaledMinimumFlingVelocity() * 16;
		mMaxFlingVelocity = vc.getScaledMaximumFlingVelocity();
		mAnimationTime = listView.getContext().getResources()
				.getInteger(android.R.integer.config_shortAnimTime);
		mListView = listView;
		mCallbacks = callbacks;
	}

	/**
	 * Enables or disables (pauses or resumes) watching for swipe-to-dismiss
	 * gestures.
	 *
	 * @param enabled
	 *            Whether or not to watch for gestures.
	 */
	public void setEnabled(boolean enabled) {
		mPaused = !enabled;
	}

	/**
	 * Returns an {@link AbsListView.OnScrollListener} to be added to the
	 * {@link ListView} using
	 * {@link ListView#setOnScrollListener(AbsListView.OnScrollListener)}. If a
	 * scroll listener is already assigned, the caller should still pass scroll
	 * changes through to this listener. This will ensure that this
	 * {@link SwipeDismissListViewTouchListener} is paused during list view
	 * scrolling.</p>
	 *
	 * @see SwipeDismissListViewTouchListener
	 */
	public AbsListView.OnScrollListener makeScrollListener() {
		return new AbsListView.OnScrollListener() {
			@Override
			public void onScrollStateChanged(AbsListView absListView,
					int scrollState) {
				setEnabled(scrollState != AbsListView.OnScrollListener.SCROLL_STATE_TOUCH_SCROLL);
			}

			@Override
			public void onScroll(AbsListView absListView, int i, int i1, int i2) {
			}
		};
	}

	@Override
	public boolean onTouch(View view, MotionEvent motionEvent) {
		if (mViewWidth < 2) {
			mViewWidth = mListView.getWidth();
		}

		switch (motionEvent.getActionMasked()) {
		case MotionEvent.ACTION_DOWN: {
			if (mPaused) {
				return false;
			}

			// TODO: ensure this is a finger, and set a flag

			// Find the child view that was touched (perform a hit test)
			Rect rect = new Rect();
			int childCount = mListView.getChildCount();
			int[] listViewCoords = new int[2];
			mListView.getLocationOnScreen(listViewCoords);
			int x = (int) motionEvent.getRawX() - listViewCoords[0];
			int y = (int) motionEvent.getRawY() - listViewCoords[1];
			View child;
			for (int i = 0; i < childCount; i++) {
				child = mListView.getChildAt(i);
				child.getHitRect(rect);
				if (rect.contains(x, y)) {
					mDownView = child;
					break;
				}
			}

			if (mDownView != null) {
				mDownX = motionEvent.getRawX();
				mDownY = motionEvent.getRawY();
				mDownPosition = mListView.getPositionForView(mDownView);
				if (mCallbacks.canDismiss(mDownPosition)) {
					mVelocityTracker = VelocityTracker.obtain();
					mVelocityTracker.addMovement(motionEvent);
				} else {
					mDownView = null;
				}
			}
			return false;
		}

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

			if (mDownView != null && mSwiping) {
				// cancel
				mDownView.animate().translationX(0).alpha(1)
						.setDuration(mAnimationTime).setListener(null);
			}
			mVelocityTracker.recycle();
			mVelocityTracker = null;
			mDownX = 0;
			mDownY = 0;
			mDownView = null;
			mDownPosition = ListView.INVALID_POSITION;
			mSwiping = false;
			break;
		}

		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 && mSwiping) {
				// dismiss only if flinging in the same direction as dragging
				dismiss = (velocityX < 0) == (deltaX < 0);
				dismissRight = mVelocityTracker.getXVelocity() > 0;
			}
			if (dismiss && mDownPosition != ListView.INVALID_POSITION) {
				// dismiss
				final View downView = mDownView; // mDownView gets null‘d before
													// animation ends
				final int downPosition = mDownPosition;
				++mDismissAnimationRefCount;
				mDownView.animate()
						.translationX(dismissRight ?

mViewWidth : -mViewWidth)
						.alpha(0).setDuration(mAnimationTime)
						.setListener(new AnimatorListenerAdapter() {
							@Override
							public void onAnimationEnd(Animator animation) {
								performDismiss(downView, downPosition);
							}
						});
			} else {
				// cancel
				mDownView.animate().translationX(0).alpha(1)
						.setDuration(mAnimationTime).setListener(null);
			}
			mVelocityTracker.recycle();
			mVelocityTracker = null;
			mDownX = 0;
			mDownY = 0;
			mDownView = null;
			mDownPosition = ListView.INVALID_POSITION;
			mSwiping = false;
			break;
		}

		case MotionEvent.ACTION_MOVE: {
			if (mVelocityTracker == null || mPaused) {
				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);
				mListView.requestDisallowInterceptTouchEvent(true);

				// Cancel ListView‘s touch (un-highlighting the item)
				MotionEvent cancelEvent = MotionEvent.obtain(motionEvent);
				cancelEvent
						.setAction(MotionEvent.ACTION_CANCEL
								| (motionEvent.getActionIndex() << MotionEvent.ACTION_POINTER_INDEX_SHIFT));
				mListView.onTouchEvent(cancelEvent);
				cancelEvent.recycle();
			}

			if (mSwiping) {
				mDownView.setTranslationX(deltaX - mSwipingSlop);
				mDownView.setAlpha(Math.max(0f,
						Math.min(1f, 1f - 2f * Math.abs(deltaX) / mViewWidth)));
				return true;
			}
			break;
		}
		}
		return false;
	}

	class PendingDismissData implements Comparable<PendingDismissData> {
		public int position;
		public View view;

		public PendingDismissData(int position, View view) {
			this.position = position;
			this.view = view;
		}

		@Override
		public int compareTo(PendingDismissData other) {
			// Sort by descending position
			return other.position - position;
		}
	}

	private void performDismiss(final View dismissView,
			final int dismissPosition) {
		// Animate the dismissed list item to zero-height and fire the dismiss
		// callback when
		// all dismissed list item animations have completed. This triggers
		// layout on each animation
		// frame; in the future we may want to do something smarter and more
		// performant.

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

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

		animator.addListener(new AnimatorListenerAdapter() {
			@Override
			public void onAnimationEnd(Animator animation) {
				--mDismissAnimationRefCount;
				if (mDismissAnimationRefCount == 0) {
					// No active animations, process all pending dismisses.
					// Sort by descending position
					Collections.sort(mPendingDismisses);

					int[] dismissPositions = new int[mPendingDismisses.size()];
					for (int i = mPendingDismisses.size() - 1; i >= 0; i--) {
						dismissPositions[i] = mPendingDismisses.get(i).position;
					}
					mCallbacks.onDismiss(mListView, dismissPositions);

					// Reset mDownPosition to avoid MotionEvent.ACTION_UP trying
					// to start a dismiss
					// animation with a stale position
					mDownPosition = ListView.INVALID_POSITION;

					ViewGroup.LayoutParams lp;
					for (PendingDismissData pendingDismiss : mPendingDismisses) {
						// Reset view presentation
						pendingDismiss.view.setAlpha(1f);
						pendingDismiss.view.setTranslationX(0);
						lp = pendingDismiss.view.getLayoutParams();
						lp.height = originalHeight;
						pendingDismiss.view.setLayoutParams(lp);
					}

					// Send a cancel event
					long time = SystemClock.uptimeMillis();
					MotionEvent cancelEvent = MotionEvent.obtain(time, time,
							MotionEvent.ACTION_CANCEL, 0, 0, 0);
					mListView.dispatchTouchEvent(cancelEvent);

					mPendingDismisses.clear();
				}
			}
		});

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

		mPendingDismisses.add(new PendingDismissData(dismissPosition,
				dismissView));
		animator.start();
	}
}

文件夹结构：