Question

目标

我正在尝试编写一种方法来替换我用来交换片段的代码，以便将复制和发布保持在最低限度（并保留D.R.Y。）

问题

当我尝试使用我作为参数传入的类来创建该类的新实例时，我收到错误。

错误发生在这行代码中，位于运算符的左侧（等号）：

newFragmentClass new_fragment = newFragmentClass.newInstance();

它给我的错误是：“newFragmentClass无法解析为类型”。

完整代码

    private void changeFragment(Class<?> newFragmentClass)
    {
        // Detect the current fragment
            Fragment current_fragment = getSupportFragmentManager().findFragmentById(R.id.fragment_container);

        // Create a new instance of the given class, edit later to gracefully handle errors
            newFragmentClass new_fragment = newFragmentClass.newInstance(); 

        // Switch to the new fragment
            FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
            transaction.detach(current_fragment);
            transaction.replace(R.id.fragment_container, new_fragment);
            transaction.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_FADE);
            transaction.commit();

        // Change the tab background to indicate that the tab is active, reset backgrounds for any other tabs
            findViewById(R.id.page_one_tab).setBackgroundResource(R.drawable.menu_button_background_active);
            findViewById(R.id.page_two_tab).setBackgroundResource(R.drawable.menu_button_background);
            findViewById(R.id.page_three_tab).setBackgroundResource(R.drawable.menu_button_background);

    }

    // Page One Tab Button Functionality
    public void pageOneTab (View v)
    {
        // Change the fragment to SelectPlayersFragment
        changeFragment(Page_One_Fragment.class);
    }

尝试解决方案

我一直在搜索StackOverflow和互联网很长一段时间，但却找不到解决方案。一些主题like this one似乎可以解决问题，但后来我在transaction.replace行遇到了一个错误，我找不到修复：“方法替换（int，Fragment）中的type FragmentTransaction不适用于参数（int，Object）“。

Answer 1

您可能需要以下内容：

private Fragment changeFragment(Class<? extends Fragment> newFragmentClass)  {
    Fragment current_fragment = getSupportFragmentManager().findFragmentById(R.id.fragment_container);
    // Create a new instance of the given class, edit later to gracefully handle errors
    Fragment new_fragment = null;
    try {
         new_fragment = newFragmentClass.newInstance();
    } catch (InstantiationException e) {            
        throw new RuntimeException(e); // for some reason this fragment loading has failed so crash
    } catch (IllegalAccessException e) {            
        throw new RuntimeException(e);
    } 
    FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
    transaction.detach(current_fragment);
    transaction.replace(R.id.fragment_container, new_fragment);
    // ...

Answer 2

或许更简单的解决方案是传递Fragment作为参数，而不是Class，并使用它来替换当前片段。此外，您不需要分离当前片段，这是replace()为您所做的事情。

这样的事情：

public void changeFragment(Fragment fragment) {
    FragmentManager manager = getSupportFragmentManager();
    FragmentTransaction transaction = manager.beginTransaction();
    transaction.replace(R.id.fragment_container, fragment, "tag");
    transaction.commit();
    //.....
}

你这样使用它：

changeFragment(new Page_One_Fragment());

Answer 3

我想你想要这个：

private <T extends Fragment> void changeFragment(Class<T> newFragmentClass)
{
    ...
    // Create a new instance of the given class, edit later to gracefully handle errors
    T new_fragment = newFragmentClass.newInstance(); 
    ...
}

Answer 4

因为你的＆＃34; newFragmentClass＆＃39;它只是方法的一个参数，它不是一个类型，所以你不能实例化它。按照我的代码来解决您的问题

private <T extends Fragment> void changeFragment(Class<T> newFragmentClass)
    {
        // Detect the current fragment
            Fragment current_fragment = getSupportFragmentManager().findFragmentById(R.id.content);

        // Create a new instance of the given class, edit later to gracefully handle errors
            T new_fragment = newFragmentClass.newInstance(); 

        // Switch to the player select fragment
            FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
            transaction.detach(current_fragment);
            transaction.replace(R.id.fragment_container, new_fragment);
            transaction.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_FADE);
            transaction.commit();

        // Change the tab background to indicate that the tab is active, reset backgrounds for any other tabs
            findViewById(R.id.page_one_tab).setBackgroundResource(R.drawable.menu_button_background_active);
            findViewById(R.id.page_two_tab).setBackgroundResource(R.drawable.menu_button_background);
            findViewById(R.id.page_three_tab).setBackgroundResource(R.drawable.menu_button_background);

    }

如何编写一个带有片段类的方法作为参数，这将允许我创建该片段的新实例？

4 个答案: