java - 如何在 fragment 中设置内容 View

Question

我使用了 android studio 附带的标准 fragment ，因为我认为它会简化我的事情，因为我仍在学习 java。但里面的代码太多了，我已经迷路了，不知道事情是如何工作的了。 Activity 我似乎了解基础知识，但经过一些研究， Activity 和 fragment 之间存在很大差异

我正在尝试应用我在 fragment Activity 中学到的相同原则，但这似乎不可能。它说我应该用充气机覆盖 oncreateview 但我似乎不理解背后的概念，为什么我不能使用简单的 setcontentview 并从 imageview 和 textedit 中检索内容？有解决方法还是避免 fragment 对我来说更好？

    package com.venomdev.safestorage;

import android.app.Activity;
import android.content.Context;
import android.net.Uri;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.ImageView;


/**
 * A simple {@link Fragment} subclass.
 * Activities that contain this fragment must implement the
 * {@link EncryptFiles.OnFragmentInteractionListener} interface
 * to handle interaction events.
 * Use the {@link EncryptFiles#newInstance} factory method to
 * create an instance of this fragment.
 *
 */
public class EncryptFiles extends Fragment {
    // TODO: Rename parameter arguments, choose names that match
    // the fragment initialization parameters, e.g. ARG_ITEM_NUMBER
    ImageView UploadFile;
    Button bUpload;
    private static final String ARG_PARAM1 = "param1";
    private static final String ARG_PARAM2 = "param2";

    // TODO: Rename and change types of parameters
    private String mParam1;
    private String mParam2;

    private OnFragmentInteractionListener mListener;

    /**
     * Use this factory method to create a new instance of
     * this fragment using the provided parameters.
     *
     * @param param1 Parameter 1.
     * @param param2 Parameter 2.
     * @return A new instance of fragment EncryptFiles.
     */
    // TODO: Rename and change types and number of parameters
    public static EncryptFiles newInstance(String param1, String param2) {
        EncryptFiles fragment = new EncryptFiles();
        Bundle args = new Bundle();
        args.putString(ARG_PARAM1, param1);
        args.putString(ARG_PARAM2, param2);
        fragment.setArguments(args);
        return fragment;
    }
    public EncryptFiles() {
        // Required empty public constructor
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.UploadFile);

        UploadFile = (ImageView) findViewById(R.id.UploadFile);


        if (getArguments() != null) {
            mParam1 = getArguments().getString(ARG_PARAM1);
            mParam2 = getArguments().getString(ARG_PARAM2);
        }
    }



    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        return inflater.inflate(R.layout.fragment_encrypt_files, container, false);
    }

    // TODO: Rename method, update argument and hook method into UI event
    public void onButtonPressed(Uri uri) {
        if (mListener != null) {
            mListener.onFragmentInteraction(uri);
        }
    }

    @Override
    public void onAttach(Activity activity) {
        super.onAttach(activity);
        if (activity instanceof OnFragmentInteractionListener) {
            mListener = (OnFragmentInteractionListener) activity;
        } else {
            throw new RuntimeException(activity.toString()
                    + " must implement OnFragmentInteractionListener");
        }
    }

    @Override
    public void onDetach() {
        super.onDetach();
        mListener = null;
    }

    /**
     * This interface must be implemented by activities that contain this
     * fragment to allow an interaction in this fragment to be communicated
     * to the activity and potentially other fragments contained in that
     * activity.
     * <p>
     * See the Android Training lesson <a href=
     * "http://developer.android.com/training/basics/fragments/communicating.html"
     * >Communicating with Other Fragments</a> for more information.
     */
    public interface OnFragmentInteractionListener {
        // TODO: Update argument type and name
        void onFragmentInteraction(Uri uri);
    }
}

Answer 1

因为Fragment位于Activity内部，不能脱离Activity使用。您不能使用 Fragment 作为 Activity 的完全替代，但您可以使用 Fragment 作为 Activity 的一部分，也可以在另一个 Activity 中重用。

您需要调用onCreateView()，因为系统会在 fragment 第一次绘制其用户界面时调用此函数。要为 fragment 绘制 UI，您必须从此方法返回一个 View ，该 View 是 fragment 布局的根。如果 fragment 不提供 UI，则可以返回 null。

要进一步了解 Fragment，您应该阅读 official documentation