如何从FileReader中获取数据

问题描述

我需要FileReader API的帮助.有什么办法可以从FileReader外部获取数据.我有一个带有类"的方法，其中使用FileReader读取图像，并且我想将图像数据放入类局部变量中(如以下代码所示).

I need a little help with FileReader API. Is there any way how to get data from FileReader outside it. I have a "class" with method, where image is read with FileReader and I want to put image data to the class local variable (as shown in following code).

我确实知道FileReader是异步工作的，而我的解决方案是错误的.有什么方法可以使其工作吗?谢谢.

I do know that FileReader works asynchronously and my solution is wrong. Is there any way how to make it work? Thank you.

CanvasState.prototype.addImage = function(inputFile) {
    var file = inputFile;
    var reader = new FileReader();
    reader.onload = this.loadImageData;
    reader.readAsDataURL(file);
}

CanvasState.prototype.loadImageData = function(e) {
    this.hasImage = true;
    this.imageData = e.target.result;
}

推荐答案

尝试一下:

CanvasState.prototype.addImage = function(inputFile) {
    var file = inputFile, self = this;
    var reader = new FileReader();
    reader.onload = function(e) {
           self.hasImage = true;
            self.imageData = e.target.result;
       };

    reader.readAsDataURL(file);
}

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