需要帮助让 Toast 出现在标签片段上

Question

当 EditText 为空时，我试图让 Toast 出现在选项卡式片段中。

这是我的 MainActivity 的 onCreate：

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        SectionsPagerAdapter sectionsPagerAdapter = new SectionsPagerAdapter(this, getSupportFragmentManager());
        ViewPager viewPager = findViewById(R.id.view_pager);
        viewPager.setAdapter(sectionsPagerAdapter);
        TabLayout tabs = findViewById(R.id.tabs);
        tabs.setupWithViewPager(viewPager);        
    }
}

我的选项卡式片段可以正常使用此代码：

public class SignupFragment extends Fragment {

    @Nullable
    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        return inflater.inflate(R.layout.fragment_signup, container, false);
    }
}

但是在像这样创建 Toast 时它不起作用：

public class SignupFragment extends Fragment {

    EditText textFillCheck;
    Button submitCheck;

    @Nullable
    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {

        submitCheck = (Button) submitCheck.findViewById(R.id.signupBtn);
        textFillCheck = (EditText) textFillCheck.findViewById(R.id.signupFirstName);
        submitCheck.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {

                if (TextUtils.isEmpty(textFillCheck.getText().toString())) {
                    Intent intent = new Intent(getActivity(), SignupFragment.class);
                    startActivity(intent);
                    Toast.makeText(getActivity(), "Please fill in all fields", Toast.LENGTH_SHORT).show();
                }
                else{Toast.makeText(getActivity(), textFillCheck.getText().toString(), Toast.LENGTH_LONG).show();
                }
            }
        });

        return inflater.inflate(R.layout.fragment_signup, container, false);
    }
}

Answer 1

您没有访问片段布局的视图，因此您在onCreateView() 中返回的布局没有附加您的逻辑。您应该将 Fragment 设置为如下所示：

public class SignupFragment extends Fragment {

    EditText textFillCheck;
    Button submitCheck;

    @Nullable
    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState){

        // Store a reference to your Fragment's inflated layout
        View root = inflater.inflate(R.layout.fragment_signup, container, false);
        
        // Use the reference to access your Fragment's views
        submitCheck = (Button) root.findViewById(R.id.signupBtn);
        textFillCheck = (EditText) root.findViewById(R.id.signupFirstName);
        
        submitCheck.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {

                if(TextUtils.isEmpty(textFillCheck.getText().toString())) {
                    Toast.makeText(getActivity(), "Please fill in all fields", Toast.LENGTH_SHORT).show();
                }else{
                    Toast.makeText(getActivity(), textFillCheck.getText().toString(), Toast.LENGTH_LONG).show();
                }
            }
        });

        // Return the inflated layout
        return root;
    }
}

Answer 2

我很惊讶为什么你的代码没有像 VIEW DOES NOT EXIST 或 NULL POINTER EXCEPTION 这样的错误，因为

首先，您在显示 Toast 之前更改活动，其次您在视图初始化后膨胀布局并且没有正确获取上下文，正确的方法是使用 OnViewCreated() 像这样

@Override
public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
    super.onViewCreated(view, savedInstanceState);

    submitCheck = (Button) view.findViewById(R.id.signupBtn);

    textFillCheck = (EditText) view.findViewById(R.id.signupFirstName);

    submitCheck.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View view) {

        if (TextUtils.isEmpty(textFillCheck.getText().toString())) {

            Toast.makeText(getActivity(), "Please fill in all fields", 
            Toast.LENGTH_SHORT).show();

            Intent intent = new Intent(getActivity(), SignupFragment.class);
            startActivity(intent);
        }
        else{
         Toast.makeText(getActivity(), textFillCheck.getText().toString(), 
         Toast.LENGTH_LONG).show();
        }
    }
});
  }