Question

我想定义一个我可以在整个应用程序中使用的导航抽屉。我按照所选答案的说明作为我的第一个方法：Same Navigation Drawer in different Activities

我做了一些修改，即从被覆盖的onCreateDrawer内部调用onCreate。我更新了后续活动以扩展DashboardActivity（＆＃34;基本活动＆＃34;来自示例）。当我启动第二个活动时，我得到一个空指针异常，抱怨当onCreateDrawer尝试设置抽屉上听到的切换时导航UI不存在。

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

以下是基础（仪表板）和后续（日志训练）活动 - 请询问是否还有其他想要查看的代码。在Android Studio中创建新的Nav Drawer Activity时，抽屉用户界面和相关活动的代码就是开箱即用的。

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);
    }

}

Answer 1

我认为您错过了drawer_layout布局中标识为activity_log_workout的抽屉。

为了使这种方法有效，您必须在所有应该有抽屉的活动布局中使用ID为drawer_layout的DrawerLayout。

我也注意到你的代码特有的东西。在扩展DashboardActivity的每个活动中，您首先设置setContentView(R.id.activity_dashboard)，然后调用onCreateDrawer()，然后您将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。

我建议你创建一个BaseDrawerActivity类来封装抽屉创建和UI绑定逻辑。然后，您只需在需要抽屉的活动中进行扩展。你可以这样做：

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();

}

如何在多个活动中使用导航抽屉

1 个答案: