从片段android启动活动时出错

Question

我的 MainActivity 中有 3 个片段，我想从 MainActivity 中的片段之一切换到 Activity2，但我的尝试总是失败。当我按下第三个片段中的“确定”按钮将我连接到 Activity2 时，我的应用程序崩溃了。我正在编写在一个教程中找到的代码。先感谢您！

public class ProfileFragment extends Fragment implements View.OnClickListener {

    private TextView tv_name,tv_email,tv_message;
    private SharedPreferences pref;
    private AppCompatButton btn_change_password,btn_logout, btn_ok;
    private EditText et_old_password,et_new_password;
    private AlertDialog dialog;
    private ProgressBar progress;


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

        View view = inflater.inflate(R.layout.fragment_profile,container,false);
        initViews(view);
        return view;

    }

    @Override
    public void onViewCreated(View view, Bundle savedInstanceState) {

        pref = getActivity().getPreferences(0);
        tv_name.setText("Здравей, "+pref.getString(Constants.NAME,"")+"!");
        tv_email.setText(pref.getString(Constants.EMAIL,""));
        btn_ok=(AppCompatButton)view.findViewById(R.id.btn_ok);
        btn_ok.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent intent=new Intent(getActivity(),activity2.class);
                startActivity(intent);
            }
        });



    }

    private void initViews(View view){

        tv_name = (TextView)view.findViewById(R.id.tv_name);
        tv_email = (TextView)view.findViewById(R.id.tv_email);
        btn_change_password = (AppCompatButton)view.findViewById(R.id.btn_chg_password);
        btn_logout = (AppCompatButton)view.findViewById(R.id.btn_logout);
        btn_ok=(AppCompatButton)view.findViewById(R.id.btn_ok);
        btn_change_password.setOnClickListener(this);
        btn_logout.setOnClickListener(this);


    }


    @Override
    public void onClick(View v) {
        switch (v.getId()){

            case R.id.btn_chg_password:
                showDialog(); //I deleted this method from the code, it doesnt have a lot in common with my question
                break;
            case R.id.btn_logout:
                logout();
                break;
}

    private void logout() {
        SharedPreferences.Editor editor = pref.edit();
        editor.putBoolean(Constants.IS_LOGGED_IN,false);
        editor.putString(Constants.EMAIL,"");
        editor.putString(Constants.NAME,"");
        editor.putString(Constants.UNIQUE_ID,"");
        editor.apply();
        goToLogin();
    }

    private void goToLogin(){

        Fragment login = new LoginFragment();
        FragmentTransaction ft = getFragmentManager().beginTransaction();
        ft.replace(R.id.fragment_frame,login);
        ft.commit();
    }


}

Answer 1

在 startActivity() 之前添加 getActivity 作为上下文 还要添加 NewTask 标志。

Intent intent = new Intent(getActivity(), activity2.class);
intent.addflags(intent.flag_activity_new_task);
getActivity().startActivity(intent);

Answer 2

您无法在片段中调用方法goToLogin()，您需要在包含此片段的活动中调用，因为您的片段不包含布局fragment_frame，它在您的活动中。

如果您想在片段中调用此方法，请将方法 goToLogin() 移动到 yourActivity 并像这样在片段中调用：

if(getActivity() instanceOf yourActivity) {
       ((youActivity) getActivity()).goToLogin();
}

Answer 3

该错误可能是因为您没有在 AndroidManifest.xml 中注册 Activity2。

但是要从 Fragment 到 Activity 进行通信，您应该使用 MainActivity 作为它的入口。虽然它看起来有点矫枉过正，但它会减轻您未来更大项目的维护。

您可以为此使用界面。

在您的 ProfileFragment 中定义并创建一个接口：

public class ProfileFragment extends Fragment implements View.OnClickListener {

    OnProfileListener mCallback;

    // Container Activity must implement this interface
    public interface OnProfileListener {
        public void onProfileButtonOkClicked();
    }

    @Override
    public void onAttach(Activity activity) {
        super.onAttach(activity);

        // This makes sure that the container activity has implemented
        // the callback interface. If not, it throws an exception
        try {
            mCallback = (OnProfileListener) activity;
        } catch (ClassCastException e) {
            throw new ClassCastException(activity.toString()
                    + " must implement OnProfileListener");
        }
    }

    ...
    ...
}

然后在你的按钮点击方法中调用接口：

@Override
public void onViewCreated(View view, Bundle savedInstanceState) {
    ...
    btn_ok=(AppCompatButton)view.findViewById(R.id.btn_ok);
    btn_ok.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            mCallback.onProfileButtonOkClicked();
        }
    });
    ...
}

最后，您需要实现 MainActivity 的接口：

public static class MainActivity extends Activity
        implements ProfileFragment.OnProfileListener{
    ...

    // When button ok in ProfileFragment clicked, this method will be called.
    public void onProfileButtonOkClicked() {
        // we can call the Activity here now.
        Intent intent=new Intent(this, activity2.class);
        startActivity(intent);
    }
}

更多详情，请阅读Communicating with Other Fragments

---

更新

对于 API 级别 >= 23 中已弃用的 onAttach()，您可以改用以下代码：

@Override
public void onAttach(Context context) {
    super.onAttach(context);
    if (context instanceof OnProfileListener) {
        mCallback = (OnProfileListener) context;
    } else {
        throw new RuntimeException(context.toString()
                + " must implement OnProfileListener");
    }
}