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java - 如何在运行时在由 android studio 创建的导航抽屉中设置默认片段

问题描述

下面是MainActivity由 android studio 导航抽屉活动生成的类，它包含 3 个名为 home、gallery 和 slideshow 的片段，以及如何在运行时更改默认片段

public class MainActivity extends AppCompatActivity {

  private AppBarConfiguration mAppBarConfiguration;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Toolbar toolbar = findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

        FloatingActionButton fab = findViewById(R.id.fab);
        DrawerLayout drawer = findViewById(R.id.drawer_layout);
        NavigationView navigationView = findViewById(R.id.nav_view);

        fab.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
                        .setAction("Action", null).show();

            }
        });

        // Passing each menu ID as a set of Ids because each
        // menu should be considered as top level destinations.
        mAppBarConfiguration = new AppBarConfiguration.Builder(R.id.nav_gallery, R.id.nav_slideshow,R.id.nav_home)
                .setDrawerLayout(drawer)
                .build();
        NavController navController = Navigation.findNavController(this, R.id.nav_host_fragment);
        NavigationUI.setupActionBarWithNavController(this, navController, mAppBarConfiguration);
        NavigationUI.setupWithNavController(navigationView, navController);

    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

    @Override
    public boolean onSupportNavigateUp() {
        NavController navController = Navigation.findNavController(this, R.id.nav_host_fragment);
        return NavigationUI.navigateUp(navController, mAppBarConfiguration)
                || super.onSupportNavigateUp();
    }
}

标签： javaandroidandroid-fragmentsnavigation-drawerandroid-architecture-navigation

解决方案

最初，必须在navGraphusingapp:startDestination属性中设置第一个/默认片段（起始目的地），否则您将获得一个RuntimeExceptionof android.view.InflateException: Binary XML file line #10: Error inflating class fragment.

因此，您的问题的答案是：您不能以编程方式设置默认片段，因为您必须首先在 xml 中设置它。但是您可以做的是在向用户显示默认片段之前，在方法中从默认导航startDestination到另一个目标片段。onCreate()

NavController负责在navGraph.

类中有几个navigate()方法的重载版本NavController，允许您在片段之间导航。

例如，要将事务设置为 Gallery 片段，您可以将其 id 传递给navigate()方法

protected void onCreate(Bundle savedInstanceState) {
    ...
    NavController navController = Navigation.findNavController(this, R.id.nav_host_fragment);
    navController.navigate(R.id.nav_gallery);
...

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