Android自定义View实现拖动自动吸边效果

自定义View，一是为了满足设计需求，二是开发者进阶的标志之一。随心所欲就是我等奋斗的目标！！！

效果

实现逻辑

• 明确需求
  1、实现控件跟随手指拖动
  2、实现控件自动贴边

• 整理思路
  1、既然要实现控件拖动，那么就离不开onTouchEvent()这个方法，需要监听里面的按下和滑动事件。
  2、 要实现自动贴边，需要监听onTouchEvent()中手指离开屏幕事件。对于贴边的过程，我们用属性动画来解决。
  3、事件的冲突问题也需要考虑，拖动、点击关系到了事件的拦截。

• 动手实现
  在需求明确、思路清晰的情况下就要开始动手实现（需要了解自定义View的一些基础API），下面代码中注释写的基本都差不多，很好理解。欢迎指出讨论！！！

完整代码

• Kotlin

class AttachButton: View {
    private var mLastRawX: Float = 0F
    private var mLastRawY: Float = 0F
    private var isDrug = false
    private var mRootMeasuredWidth = 0
    private var mRootMeasuredHeight = 0
    private var mRootTopY = 0
    private var customIsAttach = false
    private var customIsDrag = false

    constructor(context: Context) : this(context, null)
    constructor(context: Context, attrs: AttributeSet?) : this(context, attrs, 0)
    constructor(context: Context, attrs: AttributeSet?, defStyleAttr: Int) : super(
        context,
        attrs,
        defStyleAttr
    ) {
        isClickable = true
        initAttrs(context, attrs)
    }

    private fun initAttrs(context: Context, attrs: AttributeSet?) {
        attrs?.let {
            val mTypedAttay = context.obtainStyledAttributes(it, R.styleable.AttachButton)
            customIsAttach =
                mTypedAttay.getBoolean(R.styleable.AttachButton_customIsAttach, true)
            customIsDrag =
                mTypedAttay.getBoolean(R.styleable.AttachButton_customIsDrag, true)
            mTypedAttay.recycle()
        }
    }

    override fun dispatchTouchEvent(event: MotionEvent?): Boolean {
        super.dispatchTouchEvent(event)
        return true
    }

    override fun onTouchEvent(event: MotionEvent?): Boolean {
        event?.let {
            //判断是否需要滑动
            if (customIsDrag) {
                //当前手指的坐标
                val mRawX = it.rawX
                val mRawY = it.rawY
                when (it.action) {
                    MotionEvent.ACTION_DOWN -> {//手指按下
                        isDrug = false
                        //记录按下的位置
                        mLastRawX = mRawX
                        mLastRawY = mRawY
                        if (parent is ViewGroup) {
                            val mViewGroup = parent as ViewGroup
                            val location = IntArray(2)
                            mViewGroup.getLocationInWindow(location)
                            //获取父布局的高度
                            mRootMeasuredHeight = mViewGroup.measuredHeight
                            mRootMeasuredWidth = mViewGroup.measuredWidth
                            //获取父布局顶点的坐标
                            mRootTopY = location[1]
                        }
                    }
                    MotionEvent.ACTION_MOVE -> {//手指滑动
                        if (mRawX >= 0 && mRawX <= mRootMeasuredWidth && mRawY >= mRootTopY && mRawY <= (mRootMeasuredHeight + mRootTopY)) {
                            //手指X轴滑动距离
                            val differenceValueX: Float = mRawX - mLastRawX
                            //手指Y轴滑动距离
                            val differenceValueY: Float = mRawY - mLastRawY
                            //判断是否为拖动操作
                            if (!isDrug) {
                                isDrug =
                                    sqrt(((differenceValueX * differenceValueX) + (differenceValueY * differenceValueY)).toDouble()) >= 2
                            }
                            //获取手指按下的距离与控件本身X轴的距离
                            val ownX = x
                            //获取手指按下的距离与控件本身Y轴的距离
                            val ownY = y
                            //理论中X轴拖动的距离
                            var endX: Float = ownX + differenceValueX
                            //理论中Y轴拖动的距离
                            var endY: Float = ownY + differenceValueY
                            //X轴可以拖动的最大距离
                            val maxX: Float = mRootMeasuredWidth - width.toFloat()
                            //Y轴可以拖动的最大距离
                            val maxY: Float = mRootMeasuredHeight - height.toFloat()
                            //X轴边界限制
                            endX = if (endX < 0) 0F else (if (endX > maxX) maxX else endX)
                            //Y轴边界限制
                            endY = if (endY < 0) 0F else (if (endY > maxY) maxY else endY)
                            //开始移动
                            x = endX
                            y = endY
                            //记录位置
                            mLastRawX = mRawX
                            mLastRawY = mRawY
                        }
                    }

                    MotionEvent.ACTION_UP -> {//手指离开
                        if (customIsAttach) {
                            //判断是否为点击事件
                            if (isDrug) {
                                val center = mRootMeasuredWidth / 2
                                //自动贴边
                                if (mLastRawX <= center) {
                                    //向左贴边
                                    animate()
                                        .setInterpolator(BounceInterpolator())
                                        .setDuration(500)
                                        .x(0F)
                                        .start()
                                } else {
                                    //向右贴边
                                    animate()
                                        .setInterpolator(BounceInterpolator())
                                        .setDuration(500)
                                        .x(mRootMeasuredWidth - width.toFloat())
                                        .start()
                                }
                            }
                        }
                    }
                }
            }
        }
        //是否拦截事件
        return if (isDrug) isDrug else super.onTouchEvent(event)
    }
}

• Java

/**
 * 自定义View实现拖动并自动吸边效果
 * <p>
 * 处理滑动和贴边 {@link #onTouchEvent(MotionEvent)}
 * 处理事件分发 {@link #dispatchTouchEvent(MotionEvent)}
 * </p>
 *
 * @attr customIsAttach  //是否需要自动吸边
 * @attr customIsDrag    //是否可拖曳
 */
public class AttachButton extends View {
    private float mLastRawX;
    private float mLastRawY;
    private final String TAG = "AttachButton";
    private boolean isDrug = false;
    private int mRootMeasuredWidth = 0;
    private int mRootMeasuredHeight = 0;
    private int mRootTopY = 0;
    private boolean customIsAttach;
    private boolean customIsDrag;

    public AttachButton(Context context) {
        this(context, null);
    }

    public AttachButton(Context context, @Nullable AttributeSet attrs) {
        this(context, attrs, 0);
    }

    public AttachButton(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        setClickable(true);
        initAttrs(context, attrs);
    }

    /**
     * 初始化自定义属性
     */
    private void initAttrs(Context context, AttributeSet attrs) {
        TypedArray mTypedAttay = context.obtainStyledAttributes(attrs, R.styleable.AttachButton);
        customIsAttach = mTypedAttay.getBoolean(R.styleable.AttachButton_customIsAttach, true);
        customIsDrag = mTypedAttay.getBoolean(R.styleable.AttachButton_customIsDrag, true);
        mTypedAttay.recycle();
    }

    @Override
    public boolean dispatchTouchEvent(MotionEvent event) {
        super.dispatchTouchEvent(event);
        return true;
    }

    @Override
    public boolean onTouchEvent(MotionEvent ev) {
        //判断是否需要滑动
        if (customIsDrag) {
            //当前手指的坐标
            float mRawX = ev.getRawX();
            float mRawY = ev.getRawY();
            switch (ev.getAction()) {
                case MotionEvent.ACTION_DOWN://手指按下
                    isDrug = false;
                    //记录按下的位置
                    mLastRawX = mRawX;
                    mLastRawY = mRawY;
                    ViewGroup mViewGroup = (ViewGroup) getParent();
                    if (mViewGroup != null) {
                        int[] location = new int[2];
                        mViewGroup.getLocationInWindow(location);
                        //获取父布局的高度
                        mRootMeasuredHeight = mViewGroup.getMeasuredHeight();
                        mRootMeasuredWidth = mViewGroup.getMeasuredWidth();
                        //获取父布局顶点的坐标
                        mRootTopY = location[1];
                    }
                    break;
                case MotionEvent.ACTION_MOVE://手指滑动
                    if (mRawX >= 0 && mRawX <= mRootMeasuredWidth && mRawY >= mRootTopY && mRawY <= (mRootMeasuredHeight + mRootTopY)) {
                        //手指X轴滑动距离
                        float differenceValueX = mRawX - mLastRawX;
                        //手指Y轴滑动距离
                        float differenceValueY = mRawY - mLastRawY;
                        //判断是否为拖动操作
                        if (!isDrug) {
                            if (Math.sqrt(differenceValueX * differenceValueX + differenceValueY * differenceValueY) < 2) {
                                isDrug = false;
                            } else {
                                isDrug = true;
                            }
                        }
                        //获取手指按下的距离与控件本身X轴的距离
                        float ownX = getX();
                        //获取手指按下的距离与控件本身Y轴的距离
                        float ownY = getY();
                        //理论中X轴拖动的距离
                        float endX = ownX + differenceValueX;
                        //理论中Y轴拖动的距离
                        float endY = ownY + differenceValueY;
                        //X轴可以拖动的最大距离
                        float maxX = mRootMeasuredWidth - getWidth();
                        //Y轴可以拖动的最大距离
                        float maxY = mRootMeasuredHeight - getHeight();
                        //X轴边界限制
                        endX = endX < 0 ? 0 : endX > maxX ? maxX : endX;
                        //Y轴边界限制
                        endY = endY < 0 ? 0 : endY > maxY ? maxY : endY;
                        //开始移动
                        setX(endX);
                        setY(endY);
                        //记录位置
                        mLastRawX = mRawX;
                        mLastRawY = mRawY;
                    }

                    break;
                case MotionEvent.ACTION_UP://手指离开
                    //根据自定义属性判断是否需要贴边
                    if (customIsAttach) {
                        //判断是否为点击事件
                        if (isDrug) {
                            float center = mRootMeasuredWidth / 2;
                            //自动贴边
                            if (mLastRawX <= center) {
                                //向左贴边
                                AttachButton.this.animate()
                                        .setInterpolator(new BounceInterpolator())
                                        .setDuration(500)
                                        .x(0)
                                        .start();
                            } else {
                                //向右贴边
                                AttachButton.this.animate()
                                        .setInterpolator(new BounceInterpolator())
                                        .setDuration(500)
                                        .x(mRootMeasuredWidth - getWidth())
                                        .start();
                            }
                        }
                    }
                    break;
            }
        }
        //是否拦截事件
        return isDrug ? isDrug : super.onTouchEvent(ev);
    }
}

• 自定义属性

    <declare-styleable name="AttachButton">
        <!--是否需要自动吸边-->
        <attr name="customIsAttach" format="boolean" />
        <!--是否可拖曳-->
        <attr name="customIsDrag" format="boolean" />
    </declare-styleable>