Question

我在使用构造函数生成drawimage时遇到问题。我需要生成这些行和行，所以我需要能够轻松地生成这些。到目前为止我无法解决这个问题。我现在收到的错误是Uncaught ReferenceError：requestAnimFrame未定义有关如何解决此问题以使参数有效的任何想法？我需要将propertyName等于out，比如y1，y2，y2等等，因为这是我设置块的y的方式。

enemy.y = rand;
enemy.y2 = rand2;
enemy.y3 = rand3;
enemy.y4 = rand4;
enemy.y5 = rand5;
enemy.y6 = rand6;
enemy.y7 = rand7;
enemy.y8 = rand8;
enemy.y9 = rand9;

所以这里是敌人面前的代码.y1-y9＆＃39; s。

var requestAnimFrame = window.requestAnimationFrame || window.mozRequestAnimationFrame ||   window.webkitRequestAnimationFrame || window.msRequestAnimationFrame;

window.requestAnimationFrame = requestAnimFrame

function drawPiece(x,y,letter){
this.x = x;
this.y = y;
 this.letter = letter;
 var propertyName = propertyName;
 this.spawn = function(){
  for(var i = 1; i <= 9; i++){
    if(i > 1){
      var propertyName = this.letter + i;
    }
      context.drawImage(imgs[0],enemy.x,enemy[propertyName], tileWidth, tileHeight);
  }
}

enemy.propertyName = rand;
requestAnimFrame(drawPiece);
check();
}
var redblk = new drawPiece(900,rand,"y");

编辑：现在错误消失了。在构造函数中是否有足够的工作，看到这段代码？因为没有错误，但没有出现阻塞。

Answer 1

不确定代码的完整语义，但我认为您需要更改：

...
requestAnimFrame(drawPiece);
...
var redblk = new drawPiece(900,rand,"y");

为此：

var redblk = new drawPiece(900,rand,"y");
requestAnimFrame(redblk.spawn);

但是，＆＃39; spawn＆＃39;的回调上下文可能是错的我在思考（必须经过验证，但我相信＆＃39;回调中的这个将指向窗口，而不是redblk）。

您可能想要更改：

function drawPiece(x,y,letter){
this.x = x;
this.y = y;
 this.letter = letter;
 var propertyName = propertyName;
 this.spawn = function(){
  for(var i = 1; i <= 9; i++){
    if(i > 1){
      var propertyName = this.letter + i;
    }
      context.drawImage(imgs[0],enemy.x,enemy[propertyName], tileWidth, tileHeight);
  }
}

为此：

function drawPiece(x,y,letter){
this.x = x;
this.y = y;
 this.letter = letter;
 var propertyName = propertyName; //Is the RHS of this assignment properly defined?
 var ThisClosure = this;
 this.spawn = function(){
  for(var i = 1; i <= 9; i++){
    if(i > 1){
      var propertyName = ThisClosure.letter + i;
    }
      context.drawImage(imgs[0],enemy.x,enemy[propertyName], tileWidth, tileHeight);
  }
}

但是，您是否考虑过在其闭包中返回一个带参数的函数？

如果您之后不需要更改传递的参数，那么这样的事情会更优雅：

function drawPiece(x,y,letter){
 //x, y and letter are defined in the closure of the returned function.
 //judging by your use of it, propertyName is probably defined in the closure as well
 return(function(){
  for(var i = 1; i <= 9; i++){
    if(i > 1){
      var propertyName = letter + i;
    }
      context.drawImage(imgs[0],enemy.x,enemy[propertyName], tileWidth, tileHeight);
  });
}

requestAnimFrame(drawPiece(900,rand,"y"));

使用构造函数生成drawimage

1 个答案: