从活动

Question

我在我的应用程序中使用了一个标签视图...

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：尝试从字段中读取＆＃39; android.widget.TextView com.pocketdiary.ExpensesGraph.textView＆＃39;在null对象引用上                                                                                      在com.gloesolutions.pocketdiary.ComboGraph $ 1.onClick（ComboGraph.java:44）

我需要从expensgraph按钮点击combograph活动值更改textview。我尝试的每个方法都得到零点错误。 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();
  }

在活动按钮Onclick

中

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 Fragments中，您需要相应地更新TextView。如果你想在所有片段中使用相同的回调使它在循环内。

片段内部

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")
   }
}}

Answer 2

您应该在mFragmentList.add(fragment);调用替换方法，因为您的片段中的onCreateView可能无法重新初始化

Answer 3

你可以在活动中创建两个方法getter和setter，例如。 public String getDataToPass（）{return requiredtext;}，public void setDataToPass（String requiredtext）{this.requiredtext = requiredtext;}，onClick in fragment按钮，将数据传递给activity方法，例如。 btn.onClick（）{getActivity（）。setDataToPass（“your text”）;}，最后在下一个片段上OnViewCreated：获取文本为String text = getActivity（）。getDataToPass（）;