Question

我试图设置一个以导航抽屉为中心功能的项目。它应该显示应用程序内部文件目录中所有文件的名称。要更新该列表，我认为最好覆盖onDrawerOpen的{{1}}方法。主要活动的代码：

ActionBarToggle

和xml文件：

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

    DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
    ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(
            this, drawer, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close){
        @Override
        public void onDrawerOpened(View view){
            super.onDrawerOpened(view);
            File f = new File(getFilesDir().toString());
            File[] files = f.listFiles();
            String[] testString = {"Text1","Text2","Text3"};
            String[] fileNames = new String[files.length];
            for (int i = 0; i < files.length; i++) {
                fileNames[i] = files[i].getName();
            }
            ListView listView = (ListView)findViewById(R.id.file_list);
            listView.setAdapter(new ArrayAdapter<String>(MainActivity.this, android.R.layout.simple_list_item_1, testString));
        }
        //Toast.makeText(MainActivity.this,fileNames[0], Toast.LENGTH_SHORT).show();
        @Override
        public void onDrawerClosed(View view){
            super.onDrawerClosed(view);

        }

    };
    drawer.setDrawerListener(toggle);
    toggle.syncState();

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

引用的<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:app="http://schemas.android.com/apk/res-auto" android:orientation="vertical" android:layout_width="match_parent" android:layout_height="match_parent"> <android.support.design.widget.AppBarLayout android:layout_width="match_parent" android:layout_height="wrap_content" android:theme="@style/AppTheme.AppBarOverlay"> <android.support.v7.widget.Toolbar android:id="@+id/toolbar" android:layout_width="match_parent" android:layout_height="?attr/actionBarSize" android:background="?attr/colorPrimary" app:popupTheme="@style/AppTheme.PopupOverlay" /> </android.support.design.widget.AppBarLayout> <android.support.v4.widget.DrawerLayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:app="http://schemas.android.com/apk/res-auto" xmlns:tools="http://schemas.android.com/tools" android:id="@+id/drawer_layout" android:layout_width="match_parent" android:layout_height="match_parent" android:fitsSystemWindows="true" tools:openDrawer="start"> <include layout="@layout/app_bar_main" android:layout_width="match_parent" android:layout_height="match_parent" /> <android.support.design.widget.NavigationView android:id="@+id/nav_view" android:layout_width="wrap_content" android:layout_height="match_parent" android:layout_gravity="start" android:fitsSystemWindows="true" app:headerLayout="@layout/nav_header_main" app:menu="@menu/activity_main_drawer" /> </android.support.v4.widget.DrawerLayout>菜单如下所示

activity_main_drawer

所以我试图将适配器设置为带有id＆＃34; file_list＆＃34;的ListView。但是我收到了一个对该ListView的nullPointerException。任何人都可以告诉我，我做错了什么？提前谢谢！

Android - 设置适配器的NullPointerException

0 个答案: