java - 如何从 Activity 2的按钮更改 Activity 1的actionBar标题

Question

我正在尝试在activity2(设置页面)中创建一个按钮，当单击该按钮时，activity1(MainActivity)的标题将更改为我设置的内容。我一直在尝试使用接口(interface)来执行该功能，但它给了我一个空指针异常错误。

主要 Activity

@Override
    public void changeActionBarTitle(String editText){
        actionTitle = editText;
        setTitle(actionTitle);
    };

界面

public interface ActionBarInterface {
    void changeActionBarTitle(String editText);
}

设置页面( Activity 2)

public class SettingsPage extends AppCompatActivity {
    ActionBarInterface actionBarInterface;
    Button editCompanyNameButton;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_settings_page);
        setTitle("Settings");

        editCompanyNameButton = findViewById(R.id.editCompanyNameButton);
        editCompanyNameButton.setOnClickListener(new View.OnClickListener(){
            @Override
            public void onClick(View view){
                actionBarInterface.changeActionBarTitle("test");
            }
        });
    }
}

谢谢。

Answer 1

您可以在不使用界面的情况下尝试此代码

主要 Activity :

    @Override
protected void onResume() {
    setTitle(Main2Activity.title);
    super.onResume();
}

Activity 2:

public class SettingsPage extends AppCompatActivity {
Button editCompanyNameButton;
static String title;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main2);
    setTitle("Settings");

    editCompanyNameButton = findViewById(R.id.editCompanyNameButton);
    editCompanyNameButton.setOnClickListener(new View.OnClickListener(){
        @Override
        public void onClick(View view){
            title = "test";
        }
    });
}

}