I have a problem similar to this one: LUA and Corona error: Attempt To Call Method ' ' (A Nil Value) - Driving Me Crazy I have a TCell class:
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;
I have 2d array of TCell references called cells. When I assign
cells[ind1][ind2]=cells[ind3][ind4]
cells[ind1][ind2] begins to lose some properties. If I understood the link above correctly it's caused by losing the metatable association. Do I need to use setmetatable another time? How can I do it if the assignment is not done in the TCell body?
upd.
reset_metatable=function(target)
return setmetatable(target,cell_mt);
end;
cells[ind1][ind2]=cells[ind3][ind4];
cells[ind1][ind2]=cells[ind1][ind2]:reset_metatable();
isn't really helpful. upd2: deleted all code not connected with camera. Camera and TCell have no enterframe. The problem seems to be in metatables. Output gives NOW 6 1 width i 50 and after it START NOW 6 1 width is 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;
I believe you may misunderstanding variable assignment in Lua. All variables are actually references/pointers to objects. When you write:
cells[ind1][ind2]=cells[ind3][ind4]
you are throwing away (removing a reference to) the object that was pointed to by cells[ind1][ind2], and you create a second reference to the object pointed to by cells[ind3][ind4].
If you put some stuff (like the properties you think are disappearing) in cells[ind1][ind2] before the assignment, it won't be there after the assignment because that variable is now pointing at a different object.
来源：https://stackoverflow.com/questions/15716914/object-assignment-lua