Android 可拖拽的View，限制在父布局中随意拖拽；拖拽结束后可左右吸边；

实现方法一：自定义View

可随意拖动拖拽的View，限制拖动范围是父布局中；

import android.content.Context;
import android.util.AttributeSet;
import android.util.Log;
import android.view.MotionEvent;
import android.view.ViewGroup;
import android.widget.ImageView;

public class DragActionButton extends ImageView {

    private int parentHeight;
    private int parentWidth;
    private int lastX;
    private int lastY;

    private ViewGroup parent;

    public DragActionButton(Context context) {
        super(context);
    }

    public DragActionButton(Context context, AttributeSet attrs) {
        super(context, attrs);
    }

    public DragActionButton(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        int rawX = (int) event.getRawX();
        int rawY = (int) event.getRawY();
        switch (event.getAction() & MotionEvent.ACTION_MASK) {
            case MotionEvent.ACTION_DOWN:
                getParent().requestDisallowInterceptTouchEvent(true);
                lastX = rawX;
                lastY = rawY;
                if (getParent() != null) {
                    parent = (ViewGroup) getParent();
                    parentHeight = parent.getHeight();
                    parentWidth = parent.getWidth();
                }
                break;
            case MotionEvent.ACTION_MOVE:
                if (parentHeight <= 0.2 || parentWidth <= 0.2) {
                    break;
                }
                int dx = rawX - lastX;
                int dy = rawY - lastY;
                //这里修复一些华为手机无法触发点击事件
                int distance = (int) Math.sqrt(dx * dx + dy * dy);
                if (distance == 0) {
                    break;
                }
                float x = getX() + dx;
                float y = getY() + dy;
                //检测是否到达边缘 左上右下
                x = x < 0 ? 0 : x + getWidth() > parentWidth  ? parentWidth - getWidth() : x;
                y = y < 0 ? 0 : y + getHeight() > parentHeight ? parentHeight - getHeight() : y;
                setX(x);
                setY(y);
                lastX = rawX;
                lastY = rawY;
                Log.i("ACTION_MOVE", "getX=" + getX() + ";getY=" + getY() + ";parentWidth=" + parentWidth+ ";parentHeight=" + parentHeight);
                break;
            case MotionEvent.ACTION_UP:
            case MotionEvent.ACTION_CANCEL:
                this.setAlpha(1.0f);

                Log.i("ACTION_UP", "getX=" + getX() + ";getY=" + getY());
                break;
        }
        return true;
    }

}

下面是可以左右吸边的效果；

import android.animation.ObjectAnimator;
import android.content.Context;
import android.os.Handler;
import android.util.AttributeSet;
import android.util.Log;
import android.view.MotionEvent;
import android.view.View;
import android.view.ViewGroup;
import android.view.animation.DecelerateInterpolator;
import android.widget.ImageView;
import android.widget.Toast;

import androidx.annotation.Nullable;

public class DragFloatActionButton extends ImageView {

    private int parentHeight;
    private int parentWidth;
    Handler handler = new Handler();
    Runnable runnable = new Runnable() {
        @Override
        public void run() {
            setAlpha(0.3f);
        }
    };




    private int lastX;
    private int lastY;

    private ViewGroup parent;

    public DragFloatActionButton(Context context) {
        super(context);
    }

    public DragFloatActionButton(Context context,  AttributeSet attrs) {
        super(context, attrs);
    }

    public DragFloatActionButton(Context context,  AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
    }

    private int downX;
    private int downY;
    private long downTime;

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        int rawX = (int) event.getRawX();
        int rawY = (int) event.getRawY();
        switch (event.getAction() & MotionEvent.ACTION_MASK) {
            case MotionEvent.ACTION_DOWN:
                this.setAlpha(0.9f);
                getParent().requestDisallowInterceptTouchEvent(true);
                lastX = rawX;
                lastY = rawY;

                downX = rawX;
                downY = rawY;
                downTime = System.currentTimeMillis();
                if (getParent() != null) {
                    parent = (ViewGroup) getParent();
                    parentHeight = parent.getHeight();
                    parentWidth = parent.getWidth();
                }
                break;
            case MotionEvent.ACTION_MOVE:
                if (parentHeight <= 0.2 || parentWidth <= 0.2) {
                    break;
                }
                this.setAlpha(0.9f);
                int dx = rawX - lastX;
                int dy = rawY - lastY;
                //这里修复一些华为手机无法触发点击事件
                int distance = (int) Math.sqrt(dx * dx + dy * dy);
                if (distance == 0) {
                    break;
                }
                float x = getX() + dx;
                float y = getY() + dy;
                //检测是否到达边缘 左上右下
                x = x < 0 ? 0 : x + getWidth() > parentWidth  ? parentWidth - getWidth() : x;
                y = y < 0 ? 0 : y + getHeight() > parentHeight ? parentHeight - getHeight() : y;
                setX(x);
                setY(y);
                lastX = rawX;
                lastY = rawY;
                Log.i("ACTION_MOVE", "getX=" + getX() + ";getY=" + getY() + ";parentWidth=" + parentWidth+ ";parentHeight=" + parentHeight);
                break;
            case MotionEvent.ACTION_UP:
                moveHide(rawX);
                if(onClickListener != null
                        && Math.abs(downX - rawX) < 10
                        && Math.abs(downY - rawY) < 10
                        && System.currentTimeMillis() - downTime < 1000){
                    Log.i("ACTION_UP", "触发点击事件 ");
                    onClickListener.onClick(this);
                }
                break;
        }
        return true;
    }

    OnClickListener onClickListener;
    @Override
    public void setOnClickListener(@Nullable OnClickListener l) {
       onClickListener = l;
    }

    private void moveHide(int rawX) {
        if (rawX >= parentWidth / 2) {
            //靠右吸附
            animate().setInterpolator(new DecelerateInterpolator())
                    .setDuration(500)
                    .xBy(parentWidth - getWidth() - getX())
                    .start();
            myRunable();
        } else {
            //靠左吸附
            ObjectAnimator oa = ObjectAnimator.ofFloat(this, "x", getX(), 0);
            oa.setInterpolator(new DecelerateInterpolator());
            oa.setDuration(500);
            oa.start();
            myRunable();

        }
    }

    private void myRunable() {
        handler.removeCallbacks(runnable);
        handler.postDelayed(runnable, 2000);
    }

实现方法二：自定义ViewGroup

使用ViewDragHelper实现：

ViewDragHelper is a utility class for writing custom ViewGroups. It offers a number of useful operations and state tracking for allowing a user to drag and reposition views within their parent ViewGroup.

import android.content.Context;
import android.util.AttributeSet;
import android.util.Log;
import android.view.Gravity;
import android.view.MotionEvent;
import android.view.View;
import android.widget.RelativeLayout;

import androidx.customview.widget.ViewDragHelper;

public class DragViewGroup extends RelativeLayout {
    private ViewDragHelper mDragger;
    private View mDragView;


    public DragViewGroup(Context context, AttributeSet attrs) {
        super(context, attrs);
        this.setGravity(Gravity.CENTER);
        mDragger = ViewDragHelper.create(this, 1.0f, new ViewDragHelper.Callback() {
            @Override
            public boolean tryCaptureView(View child, int pointerId) {
                return true;
            }

            @Override
            public int clampViewPositionHorizontal(View child, int left, int dx) {
                final int leftBound = getPaddingLeft();
                final int rightBound = getWidth() - mDragView.getWidth();
                final int newLeft = Math.min(Math.max(left, leftBound), rightBound);
                return newLeft;

            }

            @Override
            public int clampViewPositionVertical(View child, int top, int dy) {
                final int topBound = getPaddingTop();
                final int bottomBound = getHeight() - mDragView.getHeight();
                final int newTop = Math.min(Math.max(top, topBound), bottomBound);
                return newTop;

            }


            //手指释放的时候回调
            @Override
            public void onViewReleased(View releasedChild, float xvel, float yvel) {
                Log.i("onViewReleased", "view: x :"+mDragView.getX() +"y:"+mDragView.getY()
                +"\nviewgroup: w: "+getWidth() + "h : "+getHeight());
            }


        });
    }


    @Override
    public boolean onInterceptTouchEvent(MotionEvent event) {
        return mDragger.shouldInterceptTouchEvent(event);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        mDragger.processTouchEvent(event);
        return true;
    }

    @Override
    protected void onFinishInflate() {
        super.onFinishInflate();
        mDragView = getChildAt(0);
    }
}