Fragmentからユーザ情報画面への遷移処理について説明します。
ユーザ情報画面では、UIの美しさを高めるためにアバター画像を円形に切り抜く実装を行いました。

円形画像表示用のカスタムビュー「RoundImageView」の実装：

package com.example.fuxing.widget;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.PorterDuff;
import android.graphics.PorterDuffXfermode;
import android.graphics.RectF;
import android.util.AttributeSet;

import androidx.appcompat.widget.AppCompatImageView;

public class RoundImageView extends AppCompatImageView {

    public RoundImageView(Context context, AttributeSet attrs) {
        super(context, attrs);
        init();
    }

    public RoundImageView(Context context) {
        super(context);
        init();
    }

    private final RectF roundRect = new RectF();
    private float rect_adius = 90;
    private final Paint maskPaint = new Paint();
    private final Paint zonePaint = new Paint();

    private void init() {
        maskPaint.setAntiAlias(true);
        maskPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC_IN));
        maskPaint.setFilterBitmap(true);
        zonePaint.setAntiAlias(true);
        zonePaint.setColor(Color.WHITE);
        zonePaint.setFilterBitmap(true);
        float density = getResources().getDisplayMetrics().density;
        rect_adius = rect_adius * density;
    }

    public void setRectAdius(float adius) {
        rect_adius = adius;
        invalidate();
    }

    @Override
    protected void onLayout(boolean changed, int left, int top, int right,
                            int bottom) {
        super.onLayout(changed, left, top, right, bottom);
        int w = getWidth();
        int h = getHeight();
        roundRect.set(0, 0, w, h);
    }

    @Override
    public void draw(Canvas canvas) {
        canvas.saveLayer(roundRect, zonePaint, Canvas.ALL_SAVE_FLAG);
        canvas.drawRoundRect(roundRect, rect_adius, rect_adius, zonePaint);
        canvas.saveLayer(roundRect, maskPaint, Canvas.ALL_SAVE_FLAG);
        super.draw(canvas);
        canvas.restore();
    }

}

アイテムグループを表現するカスタムビュー「ItemGroup.java」：

package com.example.fuxing.widget;

import android.content.Context;
import android.content.Intent;
import android.content.res.TypedArray;
import android.util.AttributeSet;
import android.view.LayoutInflater;
import android.view.View;
import android.widget.Button;
import android.widget.FrameLayout;
import android.widget.ImageView;
import android.widget.LinearLayout;
import android.widget.TextView;

import androidx.annotation.AttrRes;
import androidx.annotation.NonNull;
import androidx.annotation.Nullable;

import com.example.fuxing.Fragment_3;
import com.example.fuxing.MainActivity;
import com.example.fuxing.R;
import com.example.fuxing.UserActivity;

public class ItemGroup extends FrameLayout {

    private LinearLayout itemGroupLayout;
    private TextView titleTv;
    private TextView contentEdt;
    private ImageView jtRightIv;

    public TextView getContentEdt() {
        return contentEdt;
    }

    public ItemGroup(@NonNull Context context) {
        super(context);
        initView(context);
    }

    public ItemGroup(@NonNull Context context, @Nullable AttributeSet attrs) {
        super(context, attrs);
        initView(context);
        initAttrs(context, attrs);
    }

    public ItemGroup(@NonNull Context context, @Nullable AttributeSet attrs, @AttrRes int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        initView(context);
        initAttrs(context, attrs);
    }

    private void initView(Context context) {
        View view = LayoutInflater.from(context).inflate(R.layout.activity_item_group, null);
        itemGroupLayout = (LinearLayout) view.findViewById(R.id.item_group_layout);
        titleTv = (TextView) view.findViewById(R.id.title_tv);
        contentEdt = (TextView) view.findViewById(R.id.content_edt);
        jtRightIv = (ImageView) view.findViewById(R.id.jt_right_iv);
        addView(view);
    }

    private void initAttrs(Context context, AttributeSet attrs) {
        int defaultTitleColor = context.getResources().getColor(R.color.gray3);
        int defaultEdtColor = context.getResources().getColor(R.color.black);
        int defaultHintColor = context.getResources().getColor(R.color.gray3);

        TypedArray typedArray = context.obtainStyledAttributes(attrs, R.styleable.ItemGroup);
        String title = typedArray.getString(R.styleable.ItemGroup_title);
        float paddingLeft = typedArray.getDimension(R.styleable.ItemGroup_paddingLeft, 15);
        float paddingRight = typedArray.getDimension(R.styleable.ItemGroup_paddingRight, 15);
        float paddingTop = typedArray.getDimension(R.styleable.ItemGroup_paddingTop, 5);
        float paddingBottom = typedArray.getDimension(R.styleable.ItemGroup_paddingTop, 5);
        float titleSize = typedArray.getDimension(R.styleable.ItemGroup_title_size, 15);
        int titleColor = typedArray.getColor(R.styleable.ItemGroup_title_color, defaultTitleColor);
        String content = typedArray.getString(R.styleable.ItemGroup_edt_content);
        float contentSize = typedArray.getDimension(R.styleable.ItemGroup_edt_text_size, 13);
        int contentColor = typedArray.getColor(R.styleable.ItemGroup_edt_text_color, defaultEdtColor);
        String hintContent = typedArray.getString(R.styleable.ItemGroup_edt_hint_content);
        int hintColor = typedArray.getColor(R.styleable.ItemGroup_edt_hint_text_color, defaultHintColor);
        boolean isEditable = typedArray.getBoolean(R.styleable.ItemGroup_isEditable, true);
        boolean showJtIcon = typedArray.getBoolean(R.styleable.ItemGroup_jt_visible, true);
        typedArray.recycle();

        itemGroupLayout.setPadding((int) paddingLeft, (int) paddingTop, (int) paddingRight, (int) paddingBottom);
        titleTv.setText(title);
        titleTv.setTextSize(titleSize);
        titleTv.setTextColor(titleColor);

        contentEdt.setText(content);
        contentEdt.setTextSize(contentSize);
        contentEdt.setTextColor(contentColor);
        contentEdt.setHint(hintContent);
        contentEdt.setHintTextColor(hintColor);
        jtRightIv.setVisibility(showJtIcon ? View.VISIBLE : View.GONE);
    }
}

タイトルバーのカスタムビュー「TitleLayout.java」：

package com.example.fuxing.widget;

import android.app.Activity;
import android.content.Context;
import android.content.Intent;
import android.util.AttributeSet;
import android.view.LayoutInflater;
import android.view.View;
import android.widget.ImageView;
import android.widget.LinearLayout;
import android.widget.TextView;

import com.example.fuxing.LoginActivity;
import com.example.fuxing.R;
import com.example.fuxing.RegisterActivity;

public class TitleLayout extends LinearLayout {
    private ImageView iv_backward;
    private TextView tv_title, tv_forward;

    public TitleLayout(Context context, AttributeSet attrs) {
        super(context, attrs);
        LinearLayout bar_title = (LinearLayout) LayoutInflater.from(context).inflate(R.layout.activity_title, this);
        iv_backward = (ImageView) bar_title.findViewById(R.id.iv_backward);
        tv_title = (TextView) bar_title.findViewById(R.id.tv_title);
        tv_forward = (TextView) bar_title.findViewById(R.id.tv_forward);

        iv_backward.setOnClickListener(new OnClickListener() {
            @Override
            public void onClick(View v) {
                ((Activity) getContext()).finish();
            }
        });
    }
}

上記の3つのファイルはすべて「widget」パッケージに格納されています。