Javascript Angular 2 Firebase存储-上传完成时的图像预览
我试图在上传任务成功后显示上传的img,但由于异步加载,视图试图在上传完成之前显示它 方法如下:Javascript Angular 2 Firebase存储-上传完成时的图像预览,javascript,angular,firebase,firebase-storage,Javascript,Angular,Firebase,Firebase Storage,我试图在上传任务成功后显示上传的img,但由于异步加载,视图试图在上传完成之前显示它 方法如下: upload(value){ let file = value.target.files[0]; let storageRef = firebase.storage().ref('noticias/' + file.name); let uploadTask = storageRef.put(file); uploadTask.on(firebase.storage
upload(value){
let file = value.target.files[0];
let storageRef = firebase.storage().ref('noticias/' + file.name);
let uploadTask = storageRef.put(file);
uploadTask.on(firebase.storage.TaskEvent.STATE_CHANGED,
function(snapshot) {
let progress = (snapshot.bytesTransferred / snapshot.totalBytes) * 100;
console.log('Upload is ' + progress + '% done');
switch (snapshot.state) {
case firebase.storage.TaskState.PAUSED: // or 'paused'
console.log('Upload is paused');
break;
case firebase.storage.TaskState.RUNNING: // or 'running'
console.log('Upload is running');
break;
}
}, function(error) {
switch (error) {
case 'storage/unauthorized':
break;
case 'storage/canceled':
break;
case 'storage/unknown':
break;
}
}, function() {
// Upload completed successfully, now we can get the download URL
let downloadURL = uploadTask.snapshot.downloadURL;
console.log('Upload done!');
});
storageRef.getDownloadURL().then(url => this.imgUrl = url);
this.uploadedImg = true;
}
这是一种观点:
<img *ngIf="uploadedImg" [src]="imgUrl" />
方法的最后两行是加载太早的行。我还尝试将它们移动到success函数中。问题是,如果我将它们移动到那里,
这个
不再引用类,我无法更改视图中的值。失去对这个
的引用是javascript中常见的问题,有一个简单的模式来跟踪它。在success函数中移动行是正确的,只需在开始时执行以下操作:
上传(值){
让那=这;
让file=value.target.files[0];
现在,该
将始终指向原始的此
,以下操作将按预期工作:
},函数(){
//上传成功,现在我们可以获得下载URL
让downloadURL=uploadTask.snapshot.downloadURL;
log('Upload done!');
//使用原版“this”`
storageRef.getDownloadURL()。然后(url=>that.imgUrl=url);
that.uploadedImg=true;
});
最糟糕的是,我已经知道了这种模式。我刚从学习JS跳起来,太早了。。。谢谢