Android SwipeToDismiss：左滑/右滑删除ListView条目Item

《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，比如在Android 5.0及以上版本中，通知栏下拉菜单中的条目，就是这种操作效果，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，后续版本也许会有所不同）：SwipeDismissListViewTouchListener.java
和 SwipeDismissTouchListener.java 。如果只是打算简单的只是支持一个ListView列表中item左滑/右滑删除，那么仅仅只导入SwipeDismissListViewTouchListener.java这一个库文件即可。

现在就给出一个简单例子，说明如何改造一个标准ListView，使其支持左右滑动某个item然后删除。

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();

// 测试数据集。
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;
}

// 此处将执行删除，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);
}
}需要的库文件 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) motio
c426
nEvent.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();
}
}