java - 从 Activity 更改 viewpager 中的 textView 值

Question

我在我的应用程序中使用选项卡 View ...

我的代码...

public class ComboGraph extends AppCompatActivity {


Toolbar toolbar;
private TabLayout tabLayout;
private ViewPager viewPager;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_combo_graph);
    toolbar = (Toolbar) findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);
    viewPager = (ViewPager) findViewById(R.id.viewpager);
    setupViewPager(viewPager);

    tabLayout = (TabLayout) findViewById(R.id.tabs);
    tabLayout.setupWithViewPager(viewPager);

    Button next = (Button) findViewById(R.id.button8);
    final TextView textView = (TextView) findViewById(R.id.textView22);
    next.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            textView.setText(textView.getText().toString() + "a");
    ExpensesGraph expensesGraph=(ExpensesGraph)getSupportFragmentManager().findFragmentById(R.id.fragment1);
            expensesGraph.textView.setText("Hello");


        }
    });


}

private void setupViewPager(ViewPager viewPager) {
    ViewPagerAdapter adapter = new ViewPagerAdapter(getSupportFragmentManager());
    adapter.addFragment(new ExpensesGraph(), "Expenses");
    adapter.addFragment(new IncomeGraph(), "Income");
    viewPager.setAdapter(adapter);
}

class ViewPagerAdapter extends FragmentPagerAdapter {
    private final List<Fragment> mFragmentList = new ArrayList<>();
    private final List<String> mFragmentTitleList = new ArrayList<>();

    public ViewPagerAdapter(FragmentManager manager) {
        super(manager);
    }

    @Override
    public Fragment getItem(int position) {
        return mFragmentList.get(position);
    }

    @Override
    public int getCount() {
        return mFragmentList.size();
    }

    public void addFragment(Fragment fragment, String title) {
        mFragmentList.add(fragment);
        mFragmentTitleList.add(title);
    }

    @Override
    public CharSequence getPageTitle(int position) {
        return mFragmentTitleList.get(position);
    }
}

}

ExpenseGraph.java

public class ExpensesGraph extends Fragment {


TextView textView;


@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    // Inflate the layout for this fragment
    View view = inflater.inflate(R.layout.fragment_epenses_graph, container, false);
    textView = (TextView) view.findViewById(R.id.textview_fragment);
    return view;
}




}

错误日志

java.lang.NullPointerException: Attempt to read from field 'android.widget.TextView com.pocketdiary.ExpensesGraph.textView' on a null object reference at com.gloesolutions.pocketdiary.ComboGraph$1.onClick(ComboGraph.java:44)

我需要通过单击combograph按钮来更改expensgraph Activity 值中的 TextView 。我尝试的每种方法都会出现空点错误。我该如何解决这个问题？

Answer 1

为 ExpensesGraph 和 IncomeGraph 创建一个 BaseFragment，如下所示

  public abstract class BaseFragment extends Fragment {
       public abstract void updateComponent();
  }

在 Activity 按钮中单击

Button next = (Button) findViewById(R.id.button8);
final TextView textView = (TextView) findViewById(R.id.textView22);
next.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View v) {
       (BaseFragment)viewPageAdaptor.getItem(0)).updateComponent();
    }
});

在 ExpensesGraph 和 IncomeGraph fragment 内，您需要相应地更新 TextView。如果您希望在所有 fragment 中使用相同的回调，请使其在循环内。

fragment 内部

public class ExpensesGraph extends BaseFragment {

TextView textView;

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    // Inflate the layout for this fragment
    View view = inflater.inflate(R.layout.fragment_epenses_graph, container, false);
    textView = (TextView) view.findViewById(R.id.textview_fragment);
    return view;
}

public void updateComponent(){
   if(textView != null){
      textView.setText("Update your text Here")
   }
}}