如何以编程方式更改导航图的起始目标[Jetpack] [英] How to change start destination of a navigation graph programmatically [Jetpack]

问题描述

基本上，我有以下导航图:

Basically, I have the following navigation graph:

我想在到达导航图后立即将导航图的起点更改为fragment 2(以防止在按后退"按钮时返回到fragment 1-与初始屏幕一样).

I want to change my starting point in navigation graph to fragment 2 right after reaching it (in order to prevent going back to fragment 1 when pressing back button - like with the splash screen).

这是我的代码:

navGraph = navController.getGraph();
navGraph.setStartDestination(R.id.fragment2);
navController.setGraph(navGraph);

但是，很明显，它不起作用，并且按下返回按钮后，它又回到了fragment 1.

But, obviously it's not working and it gets back to fragment 1 after pressing back button.

我做错了吗? 还有其他解决方案吗?

Am I doing it wrong? Is there any other solution?

推荐答案

更新:

当您具有如下导航图时:

UPDATE:

When you have nav graph like this:

<fragment
    android:id="@+id/firstFragment"
    android:name="com.appname.package.FirstFragment" >
    <action
        android:id="@+id/action_firstFragment_to_secondFragment"
        app:destination="@id/secondFragment" /> 
</fragment>

<fragment
    android:id="@+id/secondFragment"
    android:name="com.appname.package.SecondFragment"/>

然后您要导航到第二个片段并将其设为图形的根，请指定下一个NavOptions:

And you want to navigate to the second fragment and make it root of your graph, specify the next NavOptions:

NavOptions navOptions = new NavOptions.Builder()
        .setPopUpTo(R.id.firstFragment, true)
        .build();

并使用它们进行导航:

Navigation.findNavController(view).navigate(R.id.action_firstFragment_to_secondFragment, bundle, navOptions);

setPopUpTo(int destinationId, boolean inclusive)-在导航之前弹出到给定的目的地.这将从后堆栈中弹出所有不匹配的目标，直到找到该目标为止.

setPopUpTo(int destinationId, boolean inclusive) - Pop up to a given destination before navigating. This pops all non-matching destinations from the back stack until this destination is found.

destinationId-弹出的目标，清除所有中间目标.

destinationId - The destination to pop up to, clearing all intervening destinations.

inclusive-true也可以从后堆栈中弹出给定的目的地.

inclusive - true to also pop the given destination from the back stack.

<fragment
    android:id="@+id/firstFragment"
    android:name="com.appname.package.FirstFragment" >
<action
    android:id="@+id/action_firstFragment_to_secondFragment"
    app:destination="@id/secondFragment"
    app:popUpTo="@+id/firstFragment"
    app:popUpToInclusive="true" /> 
</fragment>

<fragment
    android:id="@+id/secondFragment"
    android:name="com.appname.package.SecondFragment"/>

然后在您的代码上:

findNavController(fragment).navigate(
    FirstFragmentDirections.actionFirstFragmentToSecondFragment())

旧答案

已弃用: NavOptions中的动作和关联API的clearTask属性已被弃用.

Old answer

Deprecated: The clearTask attribute for actions and the associated API in NavOptions has been deprecated.

来源: https://developer.android.com/jetpack/docs/release-笔记

如果要将根片段更改为fragment 2(例如，按下fragment 2上的后退按钮，您将退出应用程序)，则应将下一个属性放入action或destination: >

If you want to change your root fragment to fragment 2 (e.g. after pressing back button on fragment 2 you will exit the app), you should put the next attribute to your action or destination:

app:clearTask="true"

实际上，它看起来是另一种方式:

Practically it looks in a next way:

<fragment
    android:id="@+id/firstFragment"
    android:name="com.appname.package.FirstFragment"
    android:label="fragment_first" >
    <action
        android:id="@+id/action_firstFragment_to_secondFragment"
        app:destination="@id/secondFragment"
        app:clearTask="true" /> 
</fragment>

<fragment
    android:id="@+id/secondFragment"
    android:name="com.appname.package.SecondFragment"
    android:label="fragment_second"/>

我已将app:clearTask="true"添加到动作中.

I've added app:clearTask="true" to action.

现在，当您执行从fragment 1到fragment 2的导航时，请使用以下代码:

Now when you perform navigation from fragment 1 to fragment 2 use the next code:

Navigation.findNavController(view)
        .navigate(R.id.action_firstFragment_to_secondFragment);

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