Angular 4项目中ngx-bootstrap BsDropdownModule问题求助

Hey Dan, let's work through this BsDropdownModule problem together. Looking at your package.json, I see you’ve got Bootstrap 4.0.0-beta.2 installed but no entry for ngx-bootstrap—this is likely the core issue, plus we need to make sure we’re using the right version of ngx-bootstrap that’s compatible with Angular 4. Here’s a step-by-step fix:

1. Install the Correct ngx-bootstrap Version #

Angular 4 only works with ngx-bootstrap v2.x (later versions target Angular 5+). Run this command to install the compatible version:

npm install ngx-bootstrap@2 --save
# Or if you use yarn:
yarn add ngx-bootstrap@2

2. Import BsDropdownModule into Your Angular Module #

You need to import the dropdown module into your root AppModule (or any feature module where you want to use dropdowns). Note the use of forRoot() for the root module and forChild() for feature modules:

Root Module Example (app.module.ts) #

import { NgModule } from '@angular/core';
import { BrowserModule } from '@angular/platform-browser';
import { BsDropdownModule } from 'ngx-bootstrap/dropdown';
import { AppComponent } from './app.component';

@NgModule({
  imports: [
    BrowserModule,
    // Use forRoot() in the root module to initialize the dropdown service
    BsDropdownModule.forRoot()
  ],
  declarations: [AppComponent],
  bootstrap: [AppComponent]
})
export class AppModule { }

Feature Module Example #

If you’re using dropdowns in a feature module, use forChild() instead:

import { NgModule } from '@angular/core';
import { BsDropdownModule } from 'ngx-bootstrap/dropdown';
import { FeatureComponent } from './feature.component';

@NgModule({
  imports: [
    // Use forChild() in feature modules
    BsDropdownModule.forChild()
  ],
  declarations: [FeatureComponent]
})
export class FeatureModule { }

3. Verify Bootstrap Styles Are Loaded #

Make sure Bootstrap’s CSS is properly included in your project so the dropdowns render correctly. You can do this in one of two ways:

• Option 1: Add it to your angular-cli.json (since you’re on Angular 4, this is the config file for Angular CLI):

  "styles": [
    "../node_modules/bootstrap/dist/css/bootstrap.min.css",
    "styles.css"
  ]
  

• Option 2: Import it directly in your global styles.css:

  @import '~bootstrap/dist/css/bootstrap.min.css';
  

4. Common Pitfalls to Check #

• If you get a Can't resolve 'ngx-bootstrap/dropdown' error: Double-check that you installed ngx-bootstrap v2.x—newer versions won’t work with Angular 4.
• Dropdowns don’t toggle or look broken: Confirm Bootstrap’s CSS is loaded (check your browser’s dev tools "Elements" tab to see if Bootstrap classes are being applied).
• Directives aren’t working: Ensure you’ve imported BsDropdownModule in every module where you use dropdown components/directives (don’t forget feature modules!).

内容的提问来源于stack exchange，提问作者Dan Vrajmas