如何在多个活动中使用导航抽屉 [英] How to use nav drawer in multiple activities

问题描述

我想定义一个可以在整个应用程序中使用的导航抽屉.我按照此处选择的答案的指示作为我的第一种方法:相同的导航抽屉在不同的位置活动

I want to define a single nav drawer I can use throughout my application. I followed the instructions of the chosen answer here as my first approach: Same Navigation Drawer in different Activities

我做了一些修改，即从覆盖的onCreate内部调用onCreateDrawer.我更新了我的后续活动以扩展DashboardActivity(示例中的基本活动").当我启动第二个活动时，我得到一个空指针异常，抱怨当onCreateDrawer尝试设置在抽屉上侦听的切换时，导航UI不存在.

I made a few modifications, namely calling onCreateDrawer from inside an overridden onCreate. I updated my subsequent activity to extend DashboardActivity ("base activity" from the example). When I launch my second activity I get a null pointer exception complaining that the nav UI doesn't exist when onCreateDrawer tries to set the toggle listened on the drawer.

Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v4.widget.DrawerLayout.setDrawerListener(android.support.v4.widget.DrawerLayout$DrawerListener)' on a null object reference

这是基础(仪表板)和后续(日志锻炼)活动-请询问是否还有其他代码想要查看.抽屉UI和相关活动的代码是在Android Studio中创建新的Nav Drawer Activity时开箱即用的代码.

Here are the base (dashboard) and subsequent (log workout) activity - please ask if there is other code you want to see. The code for the UI of the drawer and associated activity are what came out of the box when creating a new Nav Drawer Activity in Android Studio.

DashboardActivity.java
...
@Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_dashboard);

        onCreateDrawer();

        Realm realm = Realm.getDefaultInstance();

        RealmQuery<Exercise> query = realm.where(Exercise.class);
        RealmResults<Exercise> result = query.findAll();
        Log.d(TAG, "There are " + result.size() + " exercises ready for use.");

        FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
        fab.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Intent logWorkoutIntent = new Intent(getApplicationContext(), LogWorkoutActivity.class);
                startActivity(logWorkoutIntent);
            }
        });

        //TODO: Remove this sign out button
        Button signOutButton = (Button) findViewById(R.id.button_sign_out);
        signOutButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                FirebaseAuth.getInstance().signOut();
                Intent intent = new Intent(getApplicationContext(), LoginActivity.class);
                startActivity(intent);
                Toast.makeText(getApplicationContext(), "Signed out", Toast.LENGTH_LONG).show();
            }
        });

        //TODO: Remove this data tester
        updateUserName();
    }

    //@Override
    protected void onCreateDrawer() {
        Log.d(TAG, "onCreateDrawer called");
        //super.onCreate(savedInstanceState);

        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

        mDrawerLayout = (DrawerLayout) findViewById(R.id.drawer_layout);

        ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(
                this, mDrawerLayout, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close);
        mDrawerLayout.setDrawerListener(toggle);
        toggle.syncState();

        NavigationView navigationView = (NavigationView) findViewById(R.id.nav_view);
        navigationView.setNavigationItemSelectedListener(this);

...

-

LogWorkoutActivity.java
public class LogWorkoutActivity extends DashboardActivity {

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

        FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
        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();
            }
        });
        //getSupportActionBar().setDisplayHomeAsUpEnabled(true);
    }

}

推荐答案

我认为您在activity_log_workout布局中缺少ID为drawer_layout的抽屉.

I think you are missing a drawer with id drawer_layout in your activity_log_workout layout.

为使此方法起作用，必须在所有应具有抽屉的活动布局中使用ID为drawer_layout的DrawerLayout.

In order for this approach to work, you must have a DrawerLayout with id drawer_layout in all your activity layouts that should have the drawer.

我还注意到您的代码有一些特殊之处.在扩展DashboardActivity的每个活动中，您首先要设置setContentView(R.id.activity_dashboard)，然后调用onCreateDrawer()，然后更改内容视图并再次创建抽屉.我认为这是一种非常不理想的方法.

I also noticed something peculiar with your code. In every activity that extends DashboardActivity you are first setting setContentView(R.id.activity_dashboard), then calling onCreateDrawer(), then you are changing the content view and creating the drawer again. I think this a very suboptimal approach.

我建议您创建一个BaseDrawerActivity类来封装抽屉创建和UI绑定逻辑.然后，将其扩展到需要抽屉的活动中.您可以这样做:

I suggest you create a BaseDrawerActivity class to encapsulate the drawer creation and UI binding logic. Then you just extend it in the activities where you need a drawer. You can do it like this:

public abstract class BaseDrawerActivity extends AppCompatActivity {

    // move all your drawer related fields here

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate();

        setContentView(getLayoutResId());

        // the same method you have right now
        onCreateDrawer();
    }


    /*
     * Extending activities use this class to supply the 
     * id of their layout file. This way you can set the view 
     * only once and there is no need to create the drawer twice.
     */
    @LayoutResId
    public abstract int getLayoutResId();

}

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