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在我的角度4项目中,我实施了一些
MatSnackbar
向用户展示一些有用的信息.
除了一个案例外,所有小吃都很好用……
当用户尝试访问应用程序但令牌已过期时,我的身份验证保护将用户重定向到登录页面并显示快餐栏,
这个零食吧似乎运作良好但在控制台我可以看到这个错误：
MatSnackBarContainer_Host.html:1 ERROR Error:
ExpressionChangedAfterItHasBeenCheckedError: Expression has changed
after it was checked. Previous value: ‘undefined’. Current value:
‘visible-bottom’. It seems like the view has been created after its
parent and its children have been dirty checked. Has it been created
in a change detection hook ?
at viewDebugError (core.es5.js:8434) [angular]
at expressionChangedAfterItHasBeenCheckedError (core.es5.js:8412) [angular]
at checkBindingNoChanges (core.es5.js:8576) [angular]
at checkNoChangesNodeInline (core.es5.js:12455) [angular]
at checkNoChangesNode (core.es5.js:12429) [angular]
at debugCheckNoChangesNode (core.es5.js:13209) [angular]
at debugCheckRenderNodeFn (core.es5.js:13149) [angular]
at Object.eval [as updateRenderer] (MatSnackBarContainer_Host.html:1) [angular]
at Object.debugUpdateRenderer [as updateRenderer] (core.es5.js:13131) [angular]
at checkNoChangesView (core.es5.js:12251) [angular]
at callWithDebugContext (core.es5.js:13493) [angular]
at Object.debugCheckNoChangesView [as checkNoChangesView] (core.es5.js:13040) [angular]
at ViewRef_.webpackJsonp…/../../core/@angular/core.es5.js.ViewRef_.checkNoChanges
(core.es5.js:10197) [angular]
at vendor.bundle.js:92838:67 [angular] View_MatSnackBarContainer_Host_0 @ MatSnackBarContainer_Host.html:1
MatSnackBarContainer_Host.html:1 ERROR CONTEXT DebugContext_
在登录页面的ngOnInit中,我显示了快餐栏：
ngOnInit() {
if (this.route.snapshot.queryParams['returnUrl']) {
this.openSnackBar(('token expired'));
}
}
–
openSnackBar(message: string,action?: string) {
return this.snackBar.open(message,action,{
duration: 3000,});
}
我该如何解决这个错误
解决方法
这不是重大问题：这是一个生命周期问题.
如果您不知道,Angular将遵循生命周期,在该生命周期中,他检查更改,分配变量等.
在你的情况下,他告诉你,在将变量标记为已检查后,你已经改变了变量的值,并且它与他混淆了.您可以在错误中看到新值：
visible-bottom
这意味着你的代码中的某个地方,你做了一个
this.myVar = 'visible-bottom';
要纠正此错误,只需将其包围在超时内即可
setTimeout(() => this.myVar = 'visible-bottom');
这将告诉Angular
I know you have checked my variable,but I need to change its value,so restart your change detection please
（编辑：李大同）
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