打破Dagger中的循环依赖

Question

我对dagger很陌生——我甚至还不知道它是否适用于我的应用程序

我有一个搜索页面，返回关于给定名人的最新消息。

我写了一个测试来验证当我们搜索一个受欢迎的名人时，结果是否出现在页面上。

page有一个searchField，它需要page在其构造函数中，所以我用于我的测试的web驱动程序可以选择它。

名人搜索页面测试

public class CelebritySearchPageTest {
    @Test
    public void testSearchResultsForKevinBaconVerifyHisPopularity() {
        CelebritySearchPage searchPage = new CelebritySearchPage();
        searchPage.searchFor("Kevin Bacon");
        Assert.assertTrue(searchPage.getNumberOfResults() > 9999999, "Verify that Kevin Bacon is still relevant");
    }
}

名人搜索页面

public class CelebritySearchPage extends Page {
    @Inject
    @Named("search field")
    TextField searchField;
    public void searchFor(String text) {
        searchField.setText(text);
        // ...
    }
    public int getNumberOfResults() {
        // ...
    }
}

名人搜索页面模块

@Module(injects = CelebritySearchPage.class)
public class CelebritySearchPageModule {
    @Provides
    @Named("search field")
    public TextField provideSearchField() {
        return new TextField(/* How do I get the page? */, "#searchField");
    }
}

public abstract class Page {
    // ...
}

文本字段

public class TextField {
    protected Page page;
    protected String selector;
    public TextField(Page page, String selector) {
        this.page = page;
        this.selector = selector;
    }
    public void setText(String text) {
        // ...
    }
}

问题是page需要searchField，而searchField需要page。我如何克服这种循环依赖?

我不能在CelebritySearchPage内部初始化searchField

Answer 1

考虑一下:

CelebritySearchPage

public class CelebritySearchPage extends Page {
    private final Lazy<TextField> searchField;
// always prefer constructor injection
// avoid @Named if possible, since the compiler cannot check the string
    @Inject
    CelebritySearchPage(@Named("search field") Lazy<TextField> searchField) {
        this.searchField = searchField; 
    }
}

文本字段

public class TextField {
    protected final Lazy<Page> page;
    protected final String selector;
    @Inject TextField(Lazy<Page> page, String selector) {
        this.page = page;
        this.selector = selector;
    }
/*
Lazy::get()
Return the underlying value, computing the value if necessary. All calls to      the same Lazy instance will return the same result.
*/
}

我想一个Lazy也应该足够了。