openseadragon添加点击事件nextButton previousButton

Question

我想添加一个单击EventListener到nextButton和previousButton并获取当前图像（通过viewer.source.getTileUrl()执行此操作）。

但是，我收到TypeError: viewer.source is null。 但它适用于getUrlBtn.addEventListener("click"[...]

我对按钮上的addHandler click事件做了什么错误？

var viewer = OpenSeadragon({ 
 
    crossOriginPolicy: 'Anonymous', 
 
    visibilityRatio: 1.0, 
 
    showRotationControl: true, 
 
    defaultZoomLevel: 1.0, 
 
    minZoomImageRatio: 0.4, 
 
    id: "osd-container", 
 
    tileSources: ["images/T/1.dzi", "images/T/2.dzi", "images/T/3.dzi", "images/T/4.dzi"], 
 
    sequenceMode: true, 
 
    showReferenceStrip: false, 
 
}); 
 

 
//works 
 
var getUrlBtn = document.getElementById("getUrl"); 
 
getUrlBtn.addEventListener("click",function(e){ 
 
    console.log("getUrl: " + viewer.source.getTileUrl()); 
 
    currentFol.innerHTML = viewer.source.getTileUrl(); 
 
}); 
 

 
//TypeError: viewer.source is null 
 
viewer.nextButton.addHandler("click",function(e){ 
 
    console.log("nextButton"); 
 
    currentFol.innerHTML = viewer.source.getTileUrl(); 
 
}); 
 
//TypeError: viewer.source is null 
 
viewer.previousButton.addHandler("click",function(e){ 
 
    console.log("previousButton"); 
 
    currentFol.innerHTML = viewer.source.getTileUrl(); 
 
}) 
 

 
//I also tried but same error as above 
 
viewer.nextButton.tracker.clickHandler = updateFol; 
 
viewer.previousButton.tracker.clickHandler = updateFol; 
 

 
var currentFol = document.getElementById("currentFol"); 
 
function updateFol(){ 
 
    console.log("next/previousButton"); 
 
    currentFol.innerHTML = viewer.source.getTileUrl(); 
 
}

<button id="getUrl">get current url</button> 
 

 
<p><span id="currentFol"></span></p>

Answer 1

也许最好的方法是只听 “页” 事件：

viewer.addHandler('page', updateFol); 

运作的？