Unity 从UI中拖拽对象放置并拖动效果 附demo

using system.collections;
using system.collections.generic;
using unityengine;
using unityengine.eventsystems;
public class selectimage : monobehaviour,ipointerdownhandler{
    //需要被实例化的预制
    public gameobject inistateprefab;
    //实例化后的对象
    private gameobject inistateobj;

    // use this for initialization
    void start () {
        if (inistateprefab==null)return;
        //实例化预制
        inistateobj=instantiate(inistateprefab) as gameobject;
        inistateobj.setactive(false);
    }
    //实现鼠标按下的接口
    public void onpointerdown(pointereventdata eventdata)
    {
        inistateobj.setactive(true);

        //将当前需要被实例化的对象传递到管理器中
        selectobjmanager.instance.attachnewobject(inistateobj);
    }
}

using system.collections;
using system.collections.generic;
using unityengine;

public class selectobjmanager : monobehaviour {

    private static selectobjmanager _instance;
    public static selectobjmanager instance {
        get { return _instance; }
    }
    //物体z轴距摄像机的长度
    public float _zdistance = 50f;
    //对象的缩放系数
    public float _scalefactor=1.2f;
    //地面层级
    public layermask _groundlayermask;
    int touchid;
    bool isdragging = false;
    bool istouchinput = false;
    //是否是有效的放置（如果放置在地面上返回true,否则为false）
    bool isplacesuccess = false;
    //当前要被放置的对象
    public gameobject currentplaceobj = null;
    //坐标在y轴上的偏移量
    public float _yoffset=0.5f;

    void awake () {
        _instance = this;
    }
    void update () {
        if (currentplaceobj == null) return;

        if (checkuserinput()){
            movecurrentplaceobj();
        }else if (isdragging){
            checkifplacesuccess();
        }
    }
    /// <summary>
    ///检测用户当前输入
    /// </summary>
    /// <returns></returns>
    bool checkuserinput () {
        #if !unity_editor&&(unity_android||unity_ios)
        if (input.touches.length > 0) {
            if (!istouchinput) {
                istouchinput = true;
                touchid = input.touches[0].fingerid;
                return true;
            } else if (input.gettouch (touchid).phase == touchphase.ended) {
                istouchinput = false;
                return false;
            } else {
                return true;
            }
        }
        return false;
        #else
        return input.getmousebutton (0);
        #endif
    }
    /// <summary>
    ///让当前对象跟随鼠标移动
    /// </summary>
    void movecurrentplaceobj () {
        isdragging = true;
        vector3 point;
        vector3 screenposition;
        #if !unity_editor&&(unity_android||unity_ios)
        touch touch = input.gettouch (touchid);
        screenposition = new vector3 (touch.position.x, touch.position.y, 0);
        #else
        screenposition = input.mouseposition;
        #endif
        ray ray = camera.main.screenpointtoray (screenposition);
        raycasthit hitinfo;
        if (physics.raycast (ray, out hitinfo, 1000, _groundlayermask)) {
            point = hitinfo.point;
            isplacesuccess = true;
        } else {
            point = ray.getpoint (_zdistance);
            isplacesuccess = false;
        }
        currentplaceobj.transform.position = point+new vector3(0,_yoffset,0);
        currentplaceobj.transform.localeulerangles = new vector3 (0, 60, 0);
    }
    /// <summary>
    ///在指定位置化一个对象
    /// </summary>
    void createplaceobj(){
        gameobject obj=instantiate(currentplaceobj) as gameobject;

        obj.transform.position=currentplaceobj.transform.position;
        obj.transform.localeulerangles=currentplaceobj.transform.localeulerangles;
        obj.transform.localscale*=_scalefactor;
        //改变这个对象的layer为drag，以便后续拖动检测
        obj.layer=layermask.nametolayer("drag");
    }
    /// <summary>
    ///检测是否放置成功
    /// </summary>
    void checkifplacesuccess(){
        if (isplacesuccess){
            createplaceobj();
        }
        isdragging=false;
        currentplaceobj.setactive(false);
        currentplaceobj=null;
    }
    /// <summary>
    /// 将要创建的对象传递给当前对象管理器
    /// </summary>
    /// <param name="newobject"></param>
    public void attachnewobject(gameobject newobject){
        if (currentplaceobj){
            currentplaceobj.setactive(false);
        }
        currentplaceobj=newobject;
    }
}

using system.collections;
using system.collections.generic;
using unityengine;

public class dragobject : monobehaviour {
    //只针对指定的层级进行拖动
    public layermask _draglayermask;
    //指定当前要拖动的对象
    public transform currenttransform;
    //是否可以拖动当前对象
    public bool isdrag = false;
    //用于存储当前需要拖动的对象在屏幕空间中的坐标
    vector3 screenpos = vector3.zero;
    //当前需要拖动对象的坐标相对于鼠标在世界空间坐标中的偏移量
    vector3 offset = vector3.zero;
    void update () {

        if (input.getmousebuttondown (0)) {
            //将鼠标输入点转化为一条射线
            ray ray = camera.main.screenpointtoray (input.mouseposition);
            raycasthit hitinfo;
            //如果当前对象与指定的层级发生碰撞，表示当前对象可以被拖动
            if (physics.raycast (ray, out hitinfo, 1000f, _draglayermask)) {
                isdrag = true;
                //将当前需要拖动的对象赋值为射线碰撞到的对象
                currenttransform = hitinfo.transform;
                //将当前对象的世界坐标转化为屏幕坐标
                screenpos = camera.main.worldtoscreenpoint (currenttransform.position);
                //将鼠标的屏幕坐标转换为世界空间坐标，再与当前要拖动的对象计算两者的偏移量
                offset = currenttransform.position - camera.main.screentoworldpoint (new vector3 (input.mouseposition.x, input.mouseposition.y, screenpos.z));
            } else {
                isdrag = false;
            }
        }
        if (input.getmousebutton (0)) {
            if (isdrag == true) {

                var currentscreenpos = new vector3 (input.mouseposition.x, input.mouseposition.y, screenpos.z);
                //鼠标的屏幕空间坐标转化为世界坐标，并加上偏移量
                var currentpos = camera.main.screentoworldpoint (currentscreenpos) + offset;
                currenttransform.position = currentpos;
            }
        }
        if (input.getmousebuttonup (0)) {
            isdrag = false;
            currenttransform = null;
        }
    }
}