Android单Activity下视图切换的返回功能实现问题

我在Android Studio中用Java开发一款日历应用，支持事件的保存、展示与编辑，包含月视图、周视图、日视图等界面。最初采用多Activity架构时，返回键可以正常实现页面回退；后来因为需求调整改为单Activity架构，通过setMonthView()、setWeek()、setDaily()等方法切换视图，但点击返回键无法回到上一个视图（比如从周视图返回月视图或日视图）。默认的onBackPressed()仅用于回退Activity，满足不了当前需求，求解决方案。

相关代码片段 #

导航菜单选择逻辑

@Override
public boolean onNavigationItemSelected(@NonNull MenuItem item) {

    switch (item.getItemId()) {
        case R.id.menuSchedule:
            setAllEvents();
            drawerLayout.closeDrawer(GravityCompat.START);

            break;
        case R.id.daysView:
            setDaily();
            drawerLayout.closeDrawer(GravityCompat.START);

            break;

        case R.id.weekView:

            setWeek();
            drawerLayout.closeDrawer(GravityCompat.START);


            break;

        case R.id.monthView:
            setMonthView();
            drawerLayout.closeDrawer(GravityCompat.START);


            break;
        case R.id.refreshItem:
            finish();
            startActivity(getIntent());
            break;
        case R.id.syncItem:
            break;

        default:
            onNavigationItemSelected(item);
    }


    return true;
}

视图切换方法示例（以月视图为例）

private void setMonthView() {
    monthYearText.setText(monthYearFromDate(CalendarUtils.selectedDate));
    ArrayList<LocalDate> daysInMonth = daysInMonthArray();


    CalendarAdapter calendarAdapter = new CalendarAdapter(daysInMonth, this, getApplicationContext());
    RecyclerView.LayoutManager layoutManager = new GridLayoutManager(getApplicationContext(), 7);


    calendarRecyclerView.setLayoutManager(layoutManager);

    calendarRecyclerView.setAdapter(calendarAdapter);
    ViewGroup.LayoutParams params = calendarRecyclerView.getLayoutParams();
    params.height=1500;
    calendarRecyclerView.setLayoutParams(params);

    monthListView.setVisibility(View.GONE);
    monthYearText.setVisibility(View.VISIBLE);
    daysOfWeekDaily.setVisibility(View.GONE);
    daysOfWeek.setVisibility(View.VISIBLE);
    prevMonth.setVisibility(View.VISIBLE);
    nextMonth.setVisibility(View.VISIBLE);
    calendarRecyclerView.setVisibility(View.VISIBLE);
    nestedScrollView.setVisibility(View.VISIBLE);


}

解决方案 #

通过栈结构记录视图切换历史，重写返回键逻辑实现视图回退，具体实现如下：

首先初始化一个栈（建议在Activity的onCreate中声明），在视图切换时将当前视图类型压入栈；重写onBackPressed()方法时，从栈中弹出当前视图，根据栈顶的历史视图类型切换回对应界面，当栈为空时再执行默认的Activity回退逻辑。

修改后的完整代码：

// 初始化栈，记录视图切换历史
private LinkedList<String> stack = new LinkedList<>();

public void onMyBackPressed() {
    // 弹出当前视图类型
    stack.removeFirst();
    // 获取上一个视图类型
    String previousViewType = stack.peekFirst();
    if (previousViewType == null) {
        // 无历史视图，执行默认Activity回退
        super.onBackPressed();
        return;
    }
    // 根据历史视图类型切换对应界面
    if (previousViewType.equals("daily")) {
        setDaily();
    } else if (previousViewType.equals("week")) {
        setWeek();
    } else if (previousViewType.equals("all")) {
        setAllEvents();
    } else if (previousViewType.equals("month")) {
        setMonthView();
    }
}

@Override
public void onBackPressed() {
    onMyBackPressed();
}

@Override
public boolean onNavigationItemSelected(@NonNull MenuItem item) {

    switch (item.getItemId()) {
        case R.id.menuSchedule:
            setAllEvents();
            stack.addFirst("all");
            drawerLayout.closeDrawer(GravityCompat.START);
            break;
        case R.id.daysView:
            setDaily();
            stack.addFirst("daily");
            drawerLayout.closeDrawer(GravityCompat.START);
            break;
        case R.id.weekView:
            setWeek();
            stack.addFirst("week");
            drawerLayout.closeDrawer(GravityCompat.START);
            break;
        case R.id.monthView:
            setMonthView();
            stack.addFirst("month");
            drawerLayout.closeDrawer(GravityCompat.START);
            break;
        case R.id.refreshItem:
            finish();
            startActivity(getIntent());
            break;
        case R.id.syncItem:
            break;
        default:
            onNavigationItemSelected(item);
    }
    return true;
}

内容的提问来源于stack exchange，提问作者Chris Damianidis