lua - 对象分配Lua

Question

我有一个与此类似的问题:LUA and Corona error: Attempt To Call Method ' ' (A Nil Value) - Driving Me Crazy
我有一个TCell类:

local TCell={};
local cell_mt = { __index=TCell };
function TCell.new(_contents_name,_x,_y)
    ...
    local ncell=
    {
        ...
    };
    function ncell:setup()
        ...
    end
    ncell:setup();
    return setmetatable(ncell,cell_mt);
end
return TCell;

我有TCell引用的二维数组，称为单元格。
当我分配

cells[ind1][ind2]=cells[ind3][ind4]

cells [ind1] [ind2]开始失去某些属性。如果我正确地理解了上面的链接，那是由于失去了元表关联造成的。我是否需要再次使用setmetatable？如果未在TCell主体中完成分配，该怎么办？

更新。

reset_metatable=function(target)
    return setmetatable(target,cell_mt);
end;
cells[ind1][ind2]=cells[ind3][ind4];
cells[ind1][ind2]=cells[ind1][ind2]:reset_metatable();

并没有真正的帮助。 upd2:删除所有未与相机连接的代码。相机和TCell没有Enterframe。问题似乎出在元表中。输出给出NOW 6 1 width i 50，然后开始输出NOW 6 1 width nil

-----------------------------------------------------------------------------------------
--
-- Main Cycle
--
-----------------------------------------------------------------------------------------

local storyboard = require( "storyboard" )
local scene = storyboard.newScene()
-- include Corona's "physics" library
local physics = require "physics"
--control_circle=display.newImageRect(C.INTERFACE_DIR..C.INTERFACE_CONTROL_CIRCLE or C.EMPTY_IMAGE,C.CARS_W,C.CARS_W,true);
local events_added=false;

stage_frames=0;
physics.start(); physics.pause()
physics.setGravity( 0,0);

local PCar=require("TCar")
local PBiped=require("TBiped");
local PCell=require("TCell");

local control_circle_len;

local cells={};
local cells_w,cells_h;
local wshift,hshift=-(C.SCREEN_THEORETICAL_W-C.SCREEN_W)/2,-(C.SCREEN_THEORETICAL_H-C.SCREEN_H)/2;


--------------------------------------------

-- forward declarations and other locals


-----------------------------------------------------------------------------------------
-- BEGINNING OF YOUR IMPLEMENTATION
-- 
-- NOTE: Code outside of listener functions (below) will only be executed once,
--       unless storyboard.removeScene() is called.
-- 
-----------------------------------------------------------------------------------------
local wsells,hcells=(C.SCREEN_W-C.SCREEN_W%C.LANDSCAPE_CELL_W)/C.LANDSCAPE_CELL_W+1,(C.SCREEN_H-C.SCREEN_H%C.LANDSCAPE_CELL_H)/C.LANDSCAPE_CELL_H+1;

local dfd=false;
local function manage_cells(cmx,cmy)
    --print("#",cmx,cmy);
    if((cmx==0 and cmy==0) or dfd)
    then
        return;
    end
    local cells_shift_w,cells_shift_h=0,0;
    if(cmx>=0)
    then
        for i=cells_w,1,-1
        do
            if(cells[i][1]:out_of_borders_w()==true)
            then
                cells_shift_w=cells_shift_w+1;
            else
                break;
            end
        end
    else
        for i=1,cells_w,1
        do
            if(cells[i][1]:out_of_borders_w()==true)
            then
                cells_shift_w=cells_shift_w-1;
            else
                break;
            end
        end
    end
    if(cmy>=0)
    then
        for i=cells_h,1,-1
        do
            if(cells[1][i]:out_of_borders_h()==true)
            then
                --[[cells[1][i].contents.rotation=45;
                dfd=true;]]
                cells_shift_h=cells_shift_h+1;
            else
                break;
            end
        end
        --return;
    else
        for i=1,cells_h,1
        do
            if(cells[1][i]:out_of_borders_h()==true)
            then
                cells_shift_h=cells_shift_h-1;
            else
                break;
            end
        end
    end
    --print("~",cells_shift_w,cells_shift_h);
    local stx,finx,sty,finy=1,cells_shift_w,1,cells_shift_h;
    if(cmx<0)
    then
        stx=cells_w+cells_shift_w;
        finx=cells_w;
    end
    if(cmy<0)
    then
        sty=cells_h+cells_shift_h;
        finy=cells_h;
    end
    for i=stx,finx,1
    do
        for j=1,cells_h,1
        do
            if(cells[i][j])
            then
                cells[i][j]:destroy();
                cells[i][j]=nil;
            end
        end
    end
    for i=1,cells_w,1
    do
        for j=sty,finy,1
        do
            if(cells[i][j])
            then
                cells[i][j]:destroy();
                cells[i][j]=nil;
            end
        end
    end
    stx,finx,sty,finy=cells_w-cells_shift_w-1,1,cells_h-cells_shift_h-1,1;
    local itx,ity=-1,-1;
    if(cmx>=0)
    then
        stx=cells_shift_w+1;
        finx=cells_w;
        itx=1;
        print(stx,finx);
    end
    if(cmy>=0)
    then
        sty=cells_shift_h+1;
        finy=cells_h;
        ity=1;
    end


    for i=stx,finx,itx
    do
        for j=1,cells_h,1
        do
            if(cells_shift_w~=0)
            then

                if(j==1)
                then
                    print(i,1,"to",i-cells_shift_w,1);
                end
                cells[i-cells_shift_w][j]=cells[i][j];
                cells[i-cells_shift_w][j]=cells[i-cells_shift_w][j].reset_metatable(cells[i][j]);
                print("++",cells[i-cells_shift_w][j].contents.width);
                cells[i][j]:destroy();
                cells[i][j]=nil;
                if(j==1)
                then
                    print(i-cells_shift_w,1,"width is",cells[i-cells_shift_w][1].contents.width);
                    if(i==7)
                    then
                        cells[6][1].debug=true;
                        print("debug is set");
                    end
                end
            end
        end
    end
    for i=1,cells_w,1
    do
        for j=sty,finy,ity
        do
            if(cells_shift_h~=0)
            then
                print("?this?",i,j);
                cells[i][j-cells_shift_h]=cells[i][j];
                cells[i][j]:destroy();
                cells[i][j]=nil;
            end
        end
    end
    for i=1,cells_w,1
    do
        for j=1,cells_h,1
        do
            if(cells[i][j]==nil)
            then
                print("*new",i,j);
                cells[i][j]=PCell.new(C.LANDSCAPE_DICTIONARY(nil,1),(i-1)*C.LANDSCAPE_CELL_W+C.LANDSCAPE_CELL_W/2-wshift-camera:getX(),(j-1)*C.LANDSCAPE_CELL_H+C.LANDSCAPE_CELL_H/2-hshift-camera:getY());
            end
        end
    end

end
local function stage_main_frame()
    print("START NOW",6,1,"width is",cells[6][1].contents.width);
    local old_camera_x,old_camera_y=camera._view.x,camera._view.y;
    if(dfd==false)
    then
        --print("&");
        camera._view.x=camera._view.x-stage_frames;
    end
    local cmx,cmy=-(camera:getX()-old_camera_x),-(camera:getY()-old_camera_y);
    manage_cells(cmx,cmy);


    stage_frames=stage_frames+1;
    print("NOW",6,1,"width is",cells[6][1].contents.width);
    return function(event)
    end

end
-- Called when the scene's view does not exist:
function scene:createScene( event )
    local group = self.view
end

-- Called immediately after scene has moved onscreen:
function control_player(event)
    car1:get_touch(event);
end
function scene:enterScene( event )
    camera:newLayer("land",1);
    camera:newLayer("bipeds",1);
    camera:newLayer("cars",1);

    i=1;
    while((i-1)*C.LANDSCAPE_CELL_W-C.LANDSCAPE_CELL_W/2-wshift<=C.SCREEN_W)
    do
        j=1;
        cells[i]={};
        while((j-1)*C.LANDSCAPE_CELL_H-C.LANDSCAPE_CELL_H/2-hshift<=C.SCREEN_H)
        do
            cells[i][j]=PCell.new(C.LANDSCAPE_DICTIONARY(nil,1),(i-1)*C.LANDSCAPE_CELL_W+C.LANDSCAPE_CELL_W/2-wshift-camera:getX(),(j-1)*C.LANDSCAPE_CELL_H+C.LANDSCAPE_CELL_H/2-hshift-camera:getY());
            j=j+1;
        end
        i=i+1;
    end
    cells_w,cells_h=#cells,#cells[1];
    local group = self.view
    physics.start();
    physics.setPositionIterations( 1 )
    if(events_added==false)
    then
        events_added=true;
        Runtime:addEventListener("touch",control_player);
        Runtime:addEventListener("enterFrame",stage_main_frame);
    end
end

-- Called when scene is about to move offscreen:
function scene:exitScene( event )
    local group = self.view

    physics.stop()

end

-- If scene's view is removed, scene:destroyScene() will be called just prior to:
function scene:destroyScene( event )
    local group = self.view

    package.loaded[physics] = nil
    physics = nil
end

-----------------------------------------------------------------------------------------
-- END OF YOUR IMPLEMENTATION
-----------------------------------------------------------------------------------------

-- "createScene" event is dispatched if scene's view does not exist
scene:addEventListener( "createScene", scene )

-- "enterScene" event is dispatched whenever scene transition has finished
scene:addEventListener( "enterScene", scene )

-- "exitScene" event is dispatched whenever before next scene's transition begins
scene:addEventListener( "exitScene", scene )

-- "destroyScene" event is dispatched before view is unloaded, which can be
-- automatically unloaded in low memory situations, or explicitly via a call to
-- storyboard.purgeScene() or storyboard.removeScene().
scene:addEventListener( "destroyScene", scene )

-----------------------------------------------------------------------------------------

return scene

。

local TCell={};
local cell_mt = { __index=TCell };
function TCell.new(_contents_name,_x,_y)
    --print(camera.x);
    if(_x==nil)
    then
        _x=0;
    end
    if(_y==nil)
    then
        _y=0;
    end
    camera:newLayer( "abacaba", 1 );
    local ncell=
    {
        contents_name=_contents_name;
        contents;
        sequence_data;
        sheet_data;

        debug=false;
        --[[main_frame;
        main_frame_handler=function(self)
            main_frame=function(event)
                if(self.contents.x+self.contents.width/2<0 or self.contents.y+self.contents.height/2<0 or self.contents.x-self.contents.width/2>C.SCREEN_W or self.contents.y-self.contents.height/2>C.SCREEN_H)
                then
                    --self:destroy();
                end
            end
            return main_frame;
        end;]]
        clear=function(self)
            if(self.debug==true)
            then
                print("CLEAR!!!!!!!!!!!!!!!!!!!!!!!!!!!!\n\n\n\n\n");
            end
            --print(self.contents);
            self.contents:removeSelf();
            camera:removeObject("land",self.contents);
        end;
        show=function(self,_contents_name,__x,__y)
            if(self.debug==true)
            then
                print("SHOW!!!!!!!!!!!!!!!!!!!!!!!!!!!!\n\n\n\n\n");
            end
            self.contents_name=_contents_name;
            if(self.contents_name~=C.EMPTY_IMAGE)
            then
                self:set_sequence_data();
            end
            if(self.contents_name~=C.EMPTY_IMAGE)
            then
                self.sheet_data=graphics.newImageSheet(self.contents_name,C.LANDSCAPE_SHEET_DATA);
                self.contents=display.newSprite(self.sheet_data,self.sequence_data);
            else
                self.contents=display.newImageRect(C.EMPTY_IMAGE,C.LANDSCAPE_CELL_W,C.LANDSCAPE_CELL_H,true);
                self.sequence_data=nil;
            end
            self.contents.x=__x;
            self.contents.y=__y;
            camera:addObject("land",self.contents);
        end;
        out_of_borders_w=function(self)
            --print(self.contents.width);
            return self.contents.x+self.contents.width/2-camera:getX()<C.LANDSCAPE_CELLS_LEFT_BORDER-C.LANDSCAPE_CELL_W or 
                self.contents.x-self.contents.width/2-camera:getX()>C.LANDSCAPE_CELLS_RIGHT_BORDER+C.LANDSCAPE_CELL_W;
        end;
        out_of_borders_h=function(self)
            return self.contents.y+self.contents.height/2-camera:getY()<C.LANDSCAPE_CELLS_UPPER_BORDER-C.LANDSCAPE_CELL_H or 
                self.contents.y-self.contents.height/2-camera:getY()>C.LANDSCAPE_CELLS_LOWER_BORDER+C.LANDSCAPE_CELL_H;
        end;
        reset_metatable=function(target)
            return setmetatable(target,cell_mt);
        end;
        set_sequence_data=function(self)
            local px=math.floor(((_x)%C.LANDSCAPE_SHEET_DATA.sheetContentWidth)/C.LANDSCAPE_SHEET_DATA.width)+1;
            local py=math.floor(((_y)%C.LANDSCAPE_SHEET_DATA.sheetContentHeight)/C.LANDSCAPE_SHEET_DATA.height)+1;
            self.sequence_data=
            {
                { name = "only", start=C.LANDSCAPE_SHEET_DATA.sheetContentWidth/C.LANDSCAPE_SHEET_DATA.width*(py-1)+px, count=1 }
            };
        end;

        destroy=function(self)
            --Runtime:removeEventListener("enterFrame",self.main_frame);
            --Runtime:removeEventListener("enterFrame",self.main_frame_handler);

            self:clear();
            if(index~=nil)
            then
                --destroy_cell(index);
            end
        end
    };
    function ncell:setup()
        self:show(self.contents_name,_x,_y);
    end
    ncell:setup();
    return setmetatable(ncell,cell_mt);
end
return TCell;

Answer 1

我相信您可能会误解Lua中的变量分配。所有变量实际上都是对象的引用/指针。当你写的时候:

cells[ind1][ind2]=cells[ind3][ind4]

您将丢弃(删除对它们的引用)cells [ind1] [ind2]指向的对象，并创建对cells [ind3] [ind4]指向的对象的第二个引用。

如果您在赋值之前将一些内容(例如您认为正在消失的属性)放在cells [ind1] [ind2]中，则赋值后该值将不再存在，因为该变量现在指向另一个对象。