javascript - drawimage 后 Canvas 中的图像立即消失

Question

我一直在使用 input type="file"来浏览图像并将其绘制在 Canvas 中。下面是我的代码:

HTML代码:

<img id="img_registrar_signature" src="" alt="ID Photo" hidden />
<canvas id='myid_registrar_signature' width='500' height='100'></canvas>
<input type="file" id="myid_registrar_signature_upload" onChange="readURL(this);" />

Javascript 代码:

function myid_open_file_dialog(elemId)
{
    var elem = document.getElementById(elemId);
    if(elem && document.createEvent) {
        var evt = document.createEvent("MouseEvents");
        evt.initEvent("click", true, false);
        elem.dispatchEvent(evt);       
    }       
}

$("#myid_registrar_signature_upload").click(function (event) {
    $("#myid_registrar_signature_upload").val("");
    myid_open_file_dialog('myid_registrar_signature_upload');                   
});

function readURL(input) {
    if (input.files && input.files[0]) {
        var reader = new FileReader();
        var image  = new Image();            
        reader.onload = function (e){                  
            image.src = e.target.result;
            $('#img_registrar_signature')
                .attr('src', e.target.result);                      

            image.onload = function() {
                var canvas= document.getElementById("myid_registrar_signature");
                var context = canvas.getContext('2d');
                img_registrar = document.getElementById("img_registrar_signature");
                context.drawImage(this,0,0, this.width, this.height, 0, 0, canvas.width, canvas.height);                                                     
            }                

        };
        reader.readAsDataURL(input.files[0]);        
    }
}

我的问题是当我浏览图像并将其显示到我的 Canvas 上时，图像被加载并立即消失。好像自动清除了。我哪里出错了？

Answer 1

你在这部分有一个递归问题:

$("#myid_registrar_signature_upload").click(function (event) {
    $("#myid_registrar_signature_upload").val("");
    myid_open_file_dialog('myid_registrar_signature_upload');                   
});

这将生成一个点击，该点击依次调用相同的方法，直到它用完堆栈(浏览器中止)。

注释掉以下行将使其工作，但您需要根据您尝试实现的目标找到解决方法(无论如何都不需要为您将要单击的按钮调用单击事件。 . :) ):

$("#myid_registrar_signature_upload").click(function (event) {
    $("#myid_registrar_signature_upload").val("");
    //myid_open_file_dialog('myid_registrar_signature_upload');                   
});

Fiddle