DragLayout

相似ScrollView的寫法，可實現子View的拖拽及復位到邊界功能

效果圖

使用方式

<com.fqxyi.utils.view.DragLayout
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <LinearLayout
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="right|bottom"
        android:background="#12345678"
        android:onClick="testViewDrag"
        android:paddingLeft="20dp"
        android:gravity="center_horizontal"
        android:layout_marginRight="10dp"
        android:orientation="vertical">

        <ImageView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:src="@mipmap/ic_launcher" />

        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="可拖拽按鈕"
            android:textColor="@android:color/black"
            android:textSize="16sp" />

    </LinearLayout>

</com.fqxyi.utils.view.DragLayout>

源代碼 求Star

package com.fqxyi.utils.view;

import android.content.Context;
import android.support.annotation.Nullable;
import android.support.v4.widget.ViewDragHelper;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;
import android.widget.FrameLayout;

/**
 * 可拖拽ViewGroup，具體的View內容由調用者決定，但只能有一個直接孩子
 * 參考文章：https://blog.csdn.net/lmj623565791/article/details/46858663
 */
public class DragLayout extends FrameLayout {

    private ViewDragHelper mDragHelper;
    //true left, false right
    private boolean leftOrRight;
    //
    private View child;

    public DragLayout(Context context) {
        super(context);
        init();
    }

    public DragLayout(Context context, @Nullable AttributeSet attrs) {
        super(context, attrs);
        init();
    }

    public DragLayout(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        init();
    }

    private void init() {
        /**
         * @param ViewGroup forParent 必須是一個ViewGroup
         * @param float sensitivity 靈敏度
         * @param Callback cb 回調
         */
        mDragHelper = ViewDragHelper.create(this, 1.0f, new ViewDragCallback());
    }

    private class ViewDragCallback extends ViewDragHelper.Callback {
        /**
         * 嘗試捕獲子view，必定要返回true
         *
         * @param view      嘗試捕獲的view
         * @param pointerId 指示器id？
         *                  這裏能夠決定哪一個子view能夠拖動
         */
        @Override
        public boolean tryCaptureView(View view, int pointerId) {
            return view == child;
        }

        /**
         * 處理水平方向上的拖動
         *
         * @param child 被拖動到view
         * @param left  移動到達的x軸的距離
         * @param dx    建議的移動的x距離
         */
        @Override
        public int clampViewPositionHorizontal(View child, int left, int dx) {
            FrameLayout.LayoutParams params = (FrameLayout.LayoutParams) child.getLayoutParams();
            // 兩個if主要是爲了讓View在ViewGroup裏面滑動
            if (params == null) {
                if (getPaddingLeft() > left) {
                    return getPaddingLeft();
                }
                if (getWidth() - child.getWidth() - getPaddingRight() < left) {
                    return getWidth() - child.getWidth() - getPaddingRight();
                }
            } else {
                if (getPaddingLeft() + params.leftMargin > left) {
                    return getPaddingLeft() + params.leftMargin;
                }
                if (getWidth() - child.getWidth() - getPaddingRight() - params.rightMargin < left) {
                    return getWidth() - child.getWidth() - getPaddingRight() - params.rightMargin;
                }
            }
            return left;
        }

        /**
         * 處理豎直方向上的拖動
         *
         * @param child 被拖動到view
         * @param top   移動到達的y軸的距離
         * @param dy    建議的移動的y距離
         */
        @Override
        public int clampViewPositionVertical(View child, int top, int dy) {
            FrameLayout.LayoutParams params = (FrameLayout.LayoutParams) child.getLayoutParams();
            // 兩個if主要是爲了讓View在ViewGroup裏面滑動
            if (params == null) {
                if (getPaddingTop() > top) {
                    return getPaddingTop();
                }
                if (getHeight() - child.getHeight() - getPaddingBottom() < top) {
                    return getHeight() - child.getHeight();
                }
            } else {
                if (getPaddingTop() + params.topMargin > top) {
                    return getPaddingTop() + params.topMargin;
                }
                if (getHeight() - child.getHeight() - getPaddingBottom() - params.bottomMargin < top) {
                    return getHeight() - child.getHeight() - getPaddingBottom() - params.bottomMargin;
                }
            }
            return top;
        }

        /**
         * 手指釋放的時候回調
         */
        @Override
        public void onViewReleased(View releasedChild, float xvel, float yvel) {
            FrameLayout.LayoutParams params = (FrameLayout.LayoutParams) releasedChild.getLayoutParams();
            if (params == null) {
                if (leftOrRight) {
                    mDragHelper.settleCapturedViewAt(getPaddingLeft(), (int) releasedChild.getY());
                } else {
                    mDragHelper.settleCapturedViewAt(getWidth() - releasedChild.getWidth() - getPaddingRight(), (int) releasedChild.getY());
                }
            } else {
                if (leftOrRight) {
                    mDragHelper.settleCapturedViewAt(getPaddingLeft() + params.leftMargin, (int) releasedChild.getY());
                } else {
                    mDragHelper.settleCapturedViewAt(getWidth() - releasedChild.getWidth() - getPaddingRight() - params.rightMargin, (int) releasedChild.getY());
                }
            }
            invalidate();
        }

        /**
         * 若是子View不消耗事件，那麼整個手勢（DOWN-MOVE*-UP）都是直接進入onTouchEvent，在onTouchEvent的DOWN的時候就肯定了captureView。
         * 若是消耗事件，那麼就會先走onInterceptTouchEvent方法，判斷是否能夠捕獲，
         * 而在判斷的過程當中會去判斷另外兩個回調的方法：getViewHorizontalDragRange和getViewVerticalDragRange，只有這兩個方法返回大於0的值才能正常的捕獲。
         */
        @Override
        public int getViewHorizontalDragRange(View child) {
            return getMeasuredWidth() - child.getMeasuredWidth();
        }

        @Override
        public int getViewVerticalDragRange(View child) {
            return getMeasuredHeight() - child.getMeasuredHeight();
        }

        /**
         * 當拖拽到狀態改變時回調
         *
         * @param state 新的狀態
         */
        @Override
        public void onViewDragStateChanged(int state) {
            switch (state) {
                case ViewDragHelper.STATE_DRAGGING:  // 正在被拖動
                    break;
                case ViewDragHelper.STATE_IDLE:  // view沒有被拖拽或者 正在進行fling/snap
                    break;
                case ViewDragHelper.STATE_SETTLING: // fling完畢後被放置到一個位置
                    break;
            }
            super.onViewDragStateChanged(state);
        }
    }

    @Override
    public void computeScroll() {
        if (mDragHelper.continueSettling(true)) {
            invalidate();
        }
    }

    @Override
    public boolean onInterceptTouchEvent(MotionEvent ev) {
        /**
         * 檢查是否能夠攔截touch事件
         * 若是onInterceptTouchEvent能夠return true 則這裏return true
         */
        return mDragHelper.shouldInterceptTouchEvent(ev);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        switch (event.getAction()) {
            case MotionEvent.ACTION_DOWN:
                if (checkNeedIntercept(event)) {
                    return true;
                }
                break;
            case MotionEvent.ACTION_UP:
                if (event.getX() >= getWidth() / 2) {
                    leftOrRight = false;
                } else {
                    leftOrRight = true;
                }
                break;
        }
        /**
         * 處理攔截到的事件
         * 這個方法會在返回前分發事件
         */
        mDragHelper.processTouchEvent(event);
        return false;
    }

    /**
     * 若是view不在邊上停靠時，觸摸view須要攔截，不然會出現沒法滑動的狀況
     */
    private boolean checkNeedIntercept(MotionEvent event) {
        FrameLayout.LayoutParams params = (FrameLayout.LayoutParams) child.getLayoutParams();
        if (params == null) {
            if (child.getX() - getPaddingLeft() != 0 && child.getX() + child.getWidth() + getPaddingRight() != getWidth()) {
                mDragHelper.processTouchEvent(event);
                return true;
            }
        } else {
            if (child.getX() - getPaddingLeft() - params.leftMargin != 0 && child.getX() + child.getWidth() + getPaddingRight() + params.rightMargin != getWidth()) {
                mDragHelper.processTouchEvent(event);
                return true;
            }
        }
        return false;
    }

    @Override
    protected void onFinishInflate() {
        super.onFinishInflate();
        if (getChildCount() != 1) {
            throw new IllegalStateException("DragLayout can host only one direct child");
        }
        child = getChildAt(0);
        child.setClickable(true);
    }
}