导读
1.我特别想充分清楚的知道ViewDragHelper到底能帮我们实现哪些常见的功能？
2.使用它实现侧滑删除功能，是我见过实现侧滑删除最简单的方式
先上图
image.png
实现步骤
这是一个Listview, 每个Item都可以左滑删除~
做的过程中，肯定是在adapter的Item布局的根布局自定义一个ViewGroup，在这个自定义ViewGroup中包含两个childView，一个是正常的显示给用户的，一个是左滑出来的那个布局。如下
接下来就是要看如何自定义这个SwipeLayout了
先粘贴源码
import android.annotation.SuppressLint;
import android.content.Context;
import android.graphics.Rect;
import android.support.v4.view.ViewCompat;
import android.support.v4.widget.ViewDragHelper;
import android.util.AttributeSet;
import android.util.Log;
import android.view.MotionEvent;
import android.view.View;
import android.view.ViewGroup;
import android.widget.FrameLayout;
/**
* 侧滑删除
*
* @author sunny
*
* @date 2016年1月31日
*
* @site www.sunnyang.com
*/
@SuppressLint("ClickableViewAccessibility")
public class SwipeLayout extends FrameLayout {
private ViewDragHelper dragHelper;
private OnSwipeChangeListener swipeChangeListener;
private Status status=Status.CLOSE;//拖拽状态 默认关闭
public Status getStatus() {
return status;
}
public void setStatus(Status status) {
this.status = status;
}
public static enum Status {
OPEN, CLOSE, DRAGING
}
//拖拽事件监听器
public static interface OnSwipeChangeListener {
void onDraging(SwipeLayout mSwipeLayout);
void onOpen(SwipeLayout mSwipeLayout);
void onClose(SwipeLayout mSwipeLayout);
void onStartOpen(SwipeLayout mSwipeLayout);
void onStartClose(SwipeLayout mSwipeLayout);
}
//重写三个构造方法
public SwipeLayout(Context context) {
this(context, null);
}
public SwipeLayout(Context context, AttributeSet attrs) {
this(context, attrs, 0);
}
public SwipeLayout(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
dragHelper = ViewDragHelper.create(this, callback);
}
private ViewDragHelper.Callback callback = new ViewDragHelper.Callback() {
//所有子View都可拖拽
public boolean tryCaptureView(View child, int pointerId) {
return true;
}
//水平拖拽后处理:移动的边界进行控制
//决定拖拽的View在水平方向上面移动到的位置
public int clampViewPositionHorizontal(View child, int left, int dx) {
Log.i("SwipeLayout", "left:" +left + ", dx:" + dx) ;
if (child == frontView) {
if (left > 0) {
return 0;
} else if (left < -range) {
return -range; //边界不能超过-range
}
} else if (child == backView) {
if (left > width) {
Log.i("SwipeLayout", "left"+left +" width:" + width );
return width;
} else if (left < width - range) {
Log.i("SwipeLayout", "left"+left +" width - range:" + (width - range));
return width - range;
}else {
Log.i("SwipeLayout", "else情况" + "left"+left +" width:" + width );
}
}
return left;
}
public void onViewPositionChanged(View changedView, int left, int top, int dx, int dy) {
if (changedView == frontView) {
backView.offsetLeftAndRight(dx);
} else if (changedView == backView) {
frontView.offsetLeftAndRight(dx);
}
//事件派发
dispatchSwipeEvent();
//兼容低版本
invalidate();
};
//松手后根据侧滑位移确定菜单打开与否
public void onViewReleased(View releasedChild, float xvel, float yvel) {
if (xvel == 0 && frontView.getLeft() < -range * 0.5f) {
open();
} else if (xvel < 0) {
open();
} else {
close();
}
};
//子View如果是clickable，必须重写的方法
public int getViewHorizontalDragRange(View child) {
return 1;
}
public int getViewVerticalDragRange(View child) {
return 1;
}
};
//根据当前状态判断回调事件
protected void dispatchSwipeEvent() {
Status preStatus=status;
status=updateStatus();
if(swipeChangeListener!=null){
swipeChangeListener.onDraging(this);
}
if(preStatus!=status&&swipeChangeListener!=null){
if(status==Status.CLOSE){
swipeChangeListener.onClose(this);
}else if(status==Status.OPEN){
swipeChangeListener.onOpen(this);
}else if(status==Status.DRAGING){
if(preStatus==Status.CLOSE){
swipeChangeListener.onStartOpen(this);
}else if(preStatus==Status.OPEN){
swipeChangeListener.onStartClose(this);
}
}
}
}
//更改状态
private Status updateStatus() {
int left=frontView.getLeft();
if(left==0){
return Status.CLOSE;
}else if(left==-range){
return Status.OPEN;
}
return Status.DRAGING;
}
private View backView;//侧滑菜单
private View frontView;//内容区域
private int height;//自定义控件布局高
private int width;//自定义控件布局宽
private int range;//侧滑菜单可滑动范围
// 持续平滑动画 高频调用
public void computeScroll() {
// 如果返回true，动画还需要继续
if (dragHelper.continueSettling(true)) {
ViewCompat.postInvalidateOnAnimation(this);
}
};
public void open() {
open(true);
}
public void open(boolean isSmooth) {
int finalLeft = -range;
if (isSmooth) {
if (dragHelper.smoothSlideViewTo(frontView, finalLeft, 0)) {
ViewCompat.postInvalidateOnAnimation(this);
}
} else {
layoutContent(true);
}
}
public void close() {
close(true);
}
public void close(boolean isSmooth) {
int finalLeft = 0;
if (isSmooth) {
if (dragHelper.smoothSlideViewTo(frontView, finalLeft, 0)) {
ViewCompat.postInvalidateOnAnimation(this);
}
} else {
layoutContent(false);
}
}
//布局子View
protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
super.onLayout(changed, left, top, right, bottom);
layoutContent(false);
}
/**
* @param isOpen 侧滑菜单是否打开
*/
private void layoutContent(boolean isOpen) {
Rect frontRect = computeFrontViewRect(isOpen);
frontView.layout(frontRect.left, frontRect.top, frontRect.right, frontRect.bottom);
Rect backRect = computeBackViewRect(frontRect);
backView.layout(backRect.left, backRect.top, backRect.right, backRect.bottom);
//调整顺序
// bringChildToFront(frontView);
}
/**
* 通过内容区域所占矩形坐标计算侧滑菜单的矩形位置区域
* @param frontRect 内容区域所占矩形
* @return
*/
private Rect computeBackViewRect(Rect frontRect) {
int left = frontRect.right;
return new Rect(left, 0, left + range, height);
}
/**
* 通过菜单打开与否isOpen计算内容区域的矩形区
* @param isOpen
* @return
*/
private Rect computeFrontViewRect(boolean isOpen) {
int left = 0;
if (isOpen) {
left = -range;
}
return new Rect(left, 0, left + width, height);
}
//获取两个View
protected void onFinishInflate() {
super.onFinishInflate();
int childCount = getChildCount();
if (childCount < 2) {
throw new IllegalStateException("you need 2 children view");
}
if (!(getChildAt(0) instanceof ViewGroup) || !(getChildAt(1) instanceof ViewGroup)) {
throw new IllegalArgumentException("your children must be instance of ViewGroup");
}
backView = getChildAt(0);//侧滑菜单
frontView = getChildAt(1);//内容区域
}
//初始化布局的高height宽width以及可滑动的范围range
protected void onSizeChanged(int w, int h, int oldw, int oldh) {
super.onSizeChanged(w, h, oldw, oldh);
height = frontView.getMeasuredHeight();
width = frontView.getMeasuredWidth();
range = backView.getMeasuredWidth();
Log.i("SwipeLayout","height :" + height + " width :" + height + " range :" + height);
}
public boolean onInterceptTouchEvent(android.view.MotionEvent ev) {
return dragHelper.shouldInterceptTouchEvent(ev);
};
@Override
public boolean onTouchEvent(MotionEvent event) {
dragHelper.processTouchEvent(event);
return true;
}
public void setSwipeChangeListener(OnSwipeChangeListener swipeChangeListener) {
this.swipeChangeListener = swipeChangeListener;
}
}
解读SwipeLayout
1.第一步当然是获取FrameLayout下的子View对象，有了子view对象，就可以很方便的获取子View的宽高。
获取子View对象的方法是onFinishInflate。
//获取两个View
protected void onFinishInflate() {
super.onFinishInflate();
int childCount = getChildCount();
if (childCount < 2) {
throw new IllegalStateException("you need 2 children view");
}
if (!(getChildAt(0) instanceof ViewGroup) || !(getChildAt(1) instanceof ViewGroup)) {
throw new IllegalArgumentException("your children must be instance of ViewGroup");
}
backView = getChildAt(0);//侧滑菜单
frontView = getChildAt(1);//内容区域
}
2.获取子View的宽高
//初始化布局的高height宽width以及可滑动的范围range
protected void onSizeChanged(int w, int h, int oldw, int oldh) {
super.onSizeChanged(w, h, oldw, oldh);
height = frontView.getMeasuredHeight();
width = frontView.getMeasuredWidth();
range = backView.getMeasuredWidth();
Log.i("SwipeLayout","height :" + height + " width :" + height + " range :" + height);
}
3.这里选择的是继承FrameLayout，那就要注意把backView(侧滑菜单)先放在屏幕最右侧的右边，即在用户刚好看不见的地方。frontView(内容区域)的宽度铺满屏幕，高度为frontView的测量高度。想到在哪个方法执行这个方法了吗？bingo，当然是onLayout了。
childView.layout(......) 方法就可以把childView放在指定的位置上
4.所以的子View都可以被拖拽，所以tryCaptureView 返回true就好
5.public int clampViewPositionHorizontal(View child, int left, int dx) ， 这个方法的内容比较难理解。我们要控制frontView的做边界
-range ~0， backView的边界是width-range ~ width
6.public void onViewPositionChanged(View changedView, int left, int top, int dx, int dy) ：调用了offsetLeftAndRight移动backView和frontView，同时添加了一些监听。
7.public void onViewReleased(View releasedChild, float xvel, float yvel)：松手后根据侧滑位移确定菜单打开与否。
8.代码当中涉及到的功能点有：
- 8.1当松手以后，view平滑的打开或者关闭的处理
- 8.2如何实时触发不同状态的监听，比如拖拽状态，打开结束状态，关闭结束状态，正要打开的状态，正要结束的状态。
- 8.3view如何依据手指的移动而移动~
源码地址
源码参考我的github地址
总结
自定义View不容易，且行且珍惜啊~
参考
http://www.cnblogs.com/aademeng/articles/6542188.html
http://www.sunnyang.com/358.html