使用 actionBar.setTitle(); 时应用程序崩溃；

Question

我有一个多列表视图，我从 Sqlite 中获取所有数据到每个列表视图

现在我想将第二个列表视图操作栏名称更改为第一个列表视图select离子标题名称

当我 select 任何一个项目（标题名称）使用意图将其传递给下一个 activity 并且我设置了操作栏但我的应用程序崩溃了这是代码

我的第一个列表视图代码

protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        listView= (ListView) findViewById(R.id.listView);
  dbHelper = new SqlLiteDbHelper(this);
        try {
            dbHelper.openDataBase();
        } catch (SQLException e) {
            e.printStackTrace();
        }
        sqLiteDatabase = dbHelper.getReadableDatabase();
        cursor = dbHelper.gettitles(sqLiteDatabase);
        String[] from = new String[]{dbHelper.TITLE};
        int[] to = new int[]{R.id.title};
        SimpleCursorAdapter adapter = new SimpleCursorAdapter(this, R.layout.title_row, cursor, from, to);
        adapter.notifyDataSetChanged();
        listView.setAdapter(adapter);
        listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
                cursor = (Cursor) (listView.getItemAtPosition(position));
                String selectedItem = cursor.getString(0);
                Intent intent = new Intent(MainActivity.this, SubcategoryActivity.class);
                intent.putExtra("selectedItem", selectedItem);
                startActivity(intent);

我的第二个列表视图代码

protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.subcategory_activity);

        ActionBar actionBar=getActionBar();
 listView2= (ListView) findViewById(R.id.listView2);
        Intent intent= getIntent();
        final String selectedData = intent.getStringExtra("selectedItem");
        actionBar.setTitle(selectedData);
        dbHelper = new SqlLiteDbHelper(this);
        try {
            dbHelper.openDataBase();
        } catch (SQLException e) {
            e.printStackTrace();
        }

        sqLiteDatabase=dbHelper.getReadableDatabase();
        cursor=dbHelper.getsubcategory(sqLiteDatabase,selectedData);
        String[] from = new String[] { dbHelper.SUBCATEGORY };
        int[] to = new int[] {R.id.subcategory };
        SimpleCursorAdapter adapter = new SimpleCursorAdapter(this,R.layout.subcategory_row,cursor,from,to);
        adapter.notifyDataSetChanged();
        listView2.setAdapter(adapter);

Logcat

java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.ky.sidd/com.example.ky.sidd.SubcategoryActivity}: java.lang.NullPointerException
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2255)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2309)
            at android.app.ActivityThread.access0(ActivityThread.java:157)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1289)
            at android.os.Handler.dispatchMessage(Handler.java:99)
            at android.os.Looper.loop(Looper.java:176)
            at android.app.ActivityThread.main(ActivityThread.java:5317)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:511)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1102)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:869)
            at dalvik.system.NativeStart.main(Native Method)
     Caused by: java.lang.NullPointerException
            at com.example.ky.sidd.SubcategoryActivity.onCreate(SubcategoryActivity.java:60)
            at android.app.Activity.performCreate(Activity.java:5326)
            at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1097)
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2218)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2309)
            at android.app.ActivityThread.access0(ActivityThread.java:157)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1289)
            at android.os.Handler.dispatchMessage(Handler.java:99)
            at android.os.Looper.loop(Looper.java:176)
            at android.app.ActivityThread.main(ActivityThread.java:5317)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:511)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1102)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:869)
            at dalvik.system.NativeStart.main(Native Method)

Answer 1

搜索 getActionbar.setTitle("") 或 getSupportActionbar.setTitle("");

Answer 2

Actionbar actionbar = getActionbar();

or

Actionbar actionbar = getSupportActionBar();

actionbar.setTitle("your title goes here.");

Answer 3

getActionBar().setTitle(Html.fromHtml("<font color='#ff0000'>ActionBartitle Name </font>"));

如果您正在使用 ActionBar 的支持库，请将 getActionBar() 更改为 getSupportActionBar()。

Answer 4

首先检查你的 selectedData 字符串和 action-bar 是否为空，因为你有空指针异常

您可以使用工具栏。并将工具栏设置为操作栏。在工具栏中添加textview。

    setSupportActionBar(mToolbar);
textView.settext("your list name");

供参考 link

使用 actionBar.setTitle(); 时应用程序崩溃；

App Crash When using actionBar.setTitle();

android

title

android-actionbar

android-sqlite