Android实现类似QQ的滑动删除效果
观察QQ的滑动删除效果，可以猜测可以滑动删除的部分主要包含两个部分，一个是内容区域（用于放置正常显示的view），另一个是操作区域（用于放置删除 按钮）。默认情况下，操作区域是不显示的，内容区域的大小是填充整个容器，操作区域始终位于内容区域的右面。当开始滑动的时候，整个容器中的所有子 view都像左滑动，如果操作区域此时是不可见的，设置为可见。
我的实现思路就是自定义一个layout SwipeLayout继承自FrameLayout。SwipeLayout包含两个子view，第一个子view是内容区域，第二个子view是操作 区域。滑动效果的控制，主要就是通过检测SwipeLayout的touch事件来实现，这里我不想自己去通过监听touch事件来实现滑动效果，那是一 个很繁琐的过程。Android support库里其实已经提供了一个很好的工具类来帮我们做这件事情ViewDragHelper。如果你看过Android原生的 DrawerLayout的代码，就会发现DrawerLayout的滑动效果也是通过ViewDragHelper类实现的。
下面先介绍一下ViewDragHelper类的使用。
首先需要在容器中创建一个ViewDragHelper类的对象
mDragHelper = ViewDragHelper.create(this, 1.0f, new ViewDragHelper.Callback());
接下来要把容器的事件处理委托给ViewDragHelper对象
@Override
public boolean onInterceptTouchEvent(MotionEvent event) {
if (mDragHelper.shouldInterceptTouchEvent(event)) {
return true;
}
return super.onInterceptTouchEvent(event);
}
@Override
public boolean onTouchEvent(MotionEvent event) {
mDragHelper.processTouchEvent(event);
return true;
}
ViewDragHelper对象来决定motion event是否是属于拖动过程。如果motion event属于拖动过程，那么触摸事件就交给ViewDragHelper来处理，ViewDragHelper在处理拖动过程的时候，会调用 ViewDragHelper.Callback对象的一系列方法。
我们可以通过ViewDragHelper.Callback来监听以下几种事件：
1.拖动的状态改变
2.被拖动的view的位置改变
3.被拖动的view被放开的时间和位置
ViewDragHelper.Callback还提供了几个方法用来影响拖动过程。
1.控制view可以拖动的范围
2.确定某个view是否可以拖动
好了，直接看代码分析吧。
在SwipeLayout的inflate事件中，获取到contentView和actionView。
@Override
protected void onFinishInflate() {
contentView = getChildAt(0);
actionView = getChildAt(1);
actionView.setVisibility(GONE);
}
在SwipeLayout的measure事件中，设置拖动的距离为actionView的宽度。
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
dragDistance = actionView.getMeasuredWidth();
}
定义DragHelperCallback extends ViewDragHelper.Callback
DragHelperCallback的tryCaptureView方法，用来确定contentView和actionView是可以拖动的
@Override
public boolean tryCaptureView(View view, int i) {
return view == contentView || view == actionView;
}
DragHelperCallback的onViewPositionChanged在被拖动的view位置改变的时候调用，如果被拖动的view是contentView，我们需要在这里更新actionView的位置，反之亦然。
@Override
public void onViewPositionChanged(View changedView, int left, int top, int dx, int dy) {
draggedX = left;
if (changedView == contentView) {
actionView.offsetLeftAndRight(dx);
} else {
contentView.offsetLeftAndRight(dx);
}
if (actionView.getVisibility() == View.GONE) {
actionView.setVisibility(View.VISIBLE);
}
invalidate();
}
DragHelperCallback的clampViewPositionHorizontal用来限制view在x轴上拖动，要实现水平拖动效果必须 要实现这个方法，我们这里因为仅仅需要实现水平拖动，所以没有实现clampViewPositionVertical方法。
@Override
public int clampViewPositionHorizontal(View child, int left, int dx) {
if (child == contentView) {
final int leftBound = getPaddingLeft();
final int minLeftBound = -leftBound - dragDistance;
final int newLeft = Math.min(Math.max(minLeftBound, left), 0);
return newLeft;
} else {
final int minLeftBound = getPaddingLeft() + contentView.getMeasuredWidth() - dragDistance;
final int maxLeftBound = getPaddingLeft() + contentView.getMeasuredWidth() + getPaddingRight();
final int newLeft = Math.min(Math.max(left, minLeftBound), maxLeftBound);
return newLeft;
}
}
DragHelperCallback的getViewHorizontalDragRange方法用来限制view可以拖动的范围
@Override
public int getViewHorizontalDragRange(View child) {
return dragDistance;
}
DragHelperCallback的onViewReleased方法中，根据滑动手势的速度以及滑动的距离来确定是否显示actionView。smoothSlideViewTo方法用来在滑动手势之后实现惯性滑动效果
@Override
public void onViewReleased(View releasedChild, float xvel, float yvel) {
super.onViewReleased(releasedChild, xvel, yvel);
boolean settleToOpen = false;
if (xvel > AUTO_OPEN_SPEED_LIMIT) {
settleToOpen = false;
} else if (xvel < -AUTO_OPEN_SPEED_LIMIT) {
settleToOpen = true;
} else if (draggedX <= -dragDistance / 2) {
settleToOpen = true;
} else if (draggedX > -dragDistance / 2) {
settleToOpen = false;
}
final int settleDestX = settleToOpen ? -dragDistance : 0;
viewDragHelper.smoothSlideViewTo(contentView, settleDestX, 0);
ViewCompat.postInvalidateOnAnimation(SwipeLayout.this);
}
完整代码：
public class SwipeLayout extends LinearLayout {
private ViewDragHelper viewDragHelper;
private View contentView;
private View actionView;
private int dragDistance;
private final double AUTO_OPEN_SPEED_LIMIT = 800.0;
private int draggedX;
public SwipeLayout(Context context) {
this(context, null);
}
public SwipeLayout(Context context, AttributeSet attrs) {
this(context, attrs, -1);
}
public SwipeLayout(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
viewDragHelper = ViewDragHelper.create(this, new DragHelperCallback());
}
@Override
protected void onFinishInflate() {
contentView = getChildAt(0);
actionView = getChildAt(1);
actionView.setVisibility(GONE);
}
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
dragDistance = actionView.getMeasuredWidth();
}
private class DragHelperCallback extends ViewDragHelper.Callback {
@Override
public boolean tryCaptureView(View view, int i) {
return view == contentView || view == actionView;
}
@Override
public void onViewPositionChanged(View changedView, int left, int top, int dx, int dy) {
draggedX = left;
if (changedView == contentView) {
actionView.offsetLeftAndRight(dx);
} else {
contentView.offsetLeftAndRight(dx);
}
if (actionView.getVisibility() == View.GONE) {
actionView.setVisibility(View.VISIBLE);
}
invalidate();
}
@Override
public int clampViewPositionHorizontal(View child, int left, int dx) {
if (child == contentView) {
final int leftBound = getPaddingLeft();
final int minLeftBound = -leftBound - dragDistance;
final int newLeft = Math.min(Math.max(minLeftBound, left), 0);
return newLeft;
} else {
final int minLeftBound = getPaddingLeft() + contentView.getMeasuredWidth() - dragDistance;
final int maxLeftBound = getPaddingLeft() + contentView.getMeasuredWidth() + getPaddingRight();
final int newLeft = Math.min(Math.max(left, minLeftBound), maxLeftBound);
return newLeft;
}
}
@Override
public int getViewHorizontalDragRange(View child) {
return dragDistance;
}
@Override
public void onViewReleased(View releasedChild, float xvel, float yvel) {
super.onViewReleased(releasedChild, xvel, yvel);
boolean settleToOpen = false;
if (xvel > AUTO_OPEN_SPEED_LIMIT) {
settleToOpen = false;
} else if (xvel < -AUTO_OPEN_SPEED_LIMIT) {
settleToOpen = true;
} else if (draggedX <= -dragDistance / 2) {
settleToOpen = true;
} else if (draggedX > -dragDistance / 2) {
settleToOpen = false;
}
final int settleDestX = settleToOpen ? -dragDistance : 0;
viewDragHelper.smoothSlideViewTo(contentView, settleDestX, 0);
ViewCompat.postInvalidateOnAnimation(SwipeLayout.this);
}
}
@Override
public boolean onInterceptTouchEvent(MotionEvent ev) {
if(viewDragHelper.shouldInterceptTouchEvent(ev)) {
return true;
}
return super.onInterceptTouchEvent(ev);
}
@Override
public boolean onTouchEvent(MotionEvent event) {
viewDragHelper.processTouchEvent(event);
return true;
}
@Override
public void computeScroll() {
super.computeScroll();
if(viewDragHelper.continueSettling(true)) {
ViewCompat.postInvalidateOnAnimation(this);
}
}
}
引用它：
<com.github.lzyzsd.swipelayoutexample.SwipeLayout android:layout_width="match_parent" android:layout_height="200dp"> <LinearLayout android:layout_width="match_parent" android:layout_height="50dp" android:background="#ffffff"> <TextView android:text="@string/hello_world" android:textSize="20sp" android:paddingLeft="20dp" android:layout_gravity="center_vertical" android:layout_width="wrap_content" android:layout_height="wrap_content"/> </LinearLayout> <LinearLayout android:layout_width="150dp" android:layout_height="50dp"> <RelativeLayout android:id="@+id/delete_button" android:clickable="true" android:layout_width="50dp" android:layout_height="50dp" android:background="#ff0000"> <View android:layout_centerInParent="true" android:layout_width="28dp" android:layout_height="28dp" android:background="@drawable/trash"/> </RelativeLayout> <RelativeLayout android:id="@+id/view_button" android:clickable="true" android:layout_width="50dp" android:layout_height="50dp" android:background="#c2c2c2"> <View android:layout_centerInParent="true" android:layout_width="28dp" android:layout_height="28dp" android:background="@drawable/magnifier"/> </RelativeLayout> <RelativeLayout android:id="@+id/star_button" android:clickable="true" android:layout_width="50dp" android:layout_height="50dp" android:background="#aaffff"> <View android:layout_centerInParent="true" android:layout_width="28dp" android:layout_height="28dp" android:background="@drawable/star"/> </RelativeLayout> </LinearLayout> </com.github.lzyzsd.swipelayoutexample.SwipeLayout>