java在片段中被压回运行主活动中的函数

Question

我有一个调用片段的活动，如下所示：

主要活动中的导航抽屉：

@SuppressWarnings("StatementWithEmptyBody")
@Override
public boolean onNavigationItemSelected(MenuItem item) {
    // Handle navigation view item clicks here.
    int id = item.getItemId();
    安卓.app.FragmentManager fragmentManager = getFragmentManager();

    if(id == R.id.nav_jobs_layout){
        fragmentManager.beginTransaction()
                .replace(R.id.content_frame, new JobsFragment())
                .addToBackStack("Jobs")
                .commit();
    }else if(id == R.id.nav_shipments_out){
        fragmentManager.beginTransaction()
                .replace(R.id.content_frame, new ShipmentsOutFragment())
                .addToBackStack("ShipmentsOut")
                .commit();
    }else if(id == R.id.logout){
        SharedPreferences preferences = getSharedPreferences("MyPreferences", Context.MODE_PRIVATE);
        Authentication auth = new Authentication(preferences);
        auth.logout();

        Intent intent = new Intent(MainActivity.this, LoginActivity.class);
        startActivity(intent);
    }
}

当我点击发货时，它会打开我的发货片段，在那里我有一个发货列表供用户选择。根据选择，我打开另一个片段，它将显示在那里。这是在这里完成的：

ShipmentFragment：

listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
    @Override
    public void onItemClick(AdapterView<?> parent, View view, int position, long id) {

        Shipment shipment = shipments.get(position);

        安卓.app.FragmentManager fragmentManager = getFragmentManager();

        ShipmentsOutDetailsFragment newFragment = new ShipmentsOutDetailsFragment();

        newFragment.shipment = shipment;

        fragmentManager.beginTransaction()
                .replace(R.id.content_frame, newFragment)
                .addToBackStack("Shipments")
                .commit();
    }
});

在下一个片段中，我将显示所选装运的详细信息。当您单击该片段时，问题就出现了。就像每次我重新加载基本装运时加载第一个片段一样

单击“上一步”时，似乎会运行onBackPressed函数，如图所示，该函数位于主活动中。我怎样才能阻止它运行？是否有一个覆盖我可以放进任何一个片段

这是主活动中的恼人的onBackPressed，我不想在我点击第二个片段时运行它，但在第一个片段上运行

@Override
public void onBackPressed() {
    DrawerLayout drawer = findViewById(R.id.drawer_layout);

    Log.v("BackPressed", "This function has been run");

    if (drawer.isDrawerOpen(GravityCompat.START)) {
        drawer.closeDrawer(GravityCompat.START);
    } else {
        super.onBackPressed();

        this.finish();
    }
}

Answer 1

尝试如下

    @Override
    public void onBackPressed() {
        DrawerLayout drawer = findViewById(R.id.drawer_layout);
        if (drawer.isDrawerOpen(GravityCompat.START)) {
            drawer.closeDrawer(GravityCompat.START);
        } else {
            int count = getFragmentManager().getBackStackEntryCount();
            if (count == 0) {
                super.onBackPressed(); //this method just will be called when there is none more fragments
            } else getFragmentManager().popBackStack();
        }
    }

Answer 2

您可以声明两个feild：

 final static int JOBS_FRAGMENT = 0;
 final static int SHIPMENTS_OUT_FRAGMENT = 1;

另一个variable可以保存当前的fragment显示：

 public int currentFragmentShown = JOBS_FRAGMENT; // Or add the fragment shown by default on the start of the activity

然后在每次更改fragment时更改currentFragmentShwon的值：

    if(id == R.id.nav_jobs_layout){
        fragmentManager.beginTransaction()
                .replace(R.id.content_frame, new JobsFragment())
                .addToBackStack("Jobs")
                .commit();
        currentFragmentShown = JOBS_FRAGMENT;
    }else if(id == R.id.nav_shipments_out){
        fragmentManager.beginTransaction()
                .replace(R.id.content_frame, new ShipmentsOutFragment())
                .addToBackStack("ShipmentsOut")
                .commit();
        currentFragmentShown = SHIPMENTS_OUT_FRAGMENT;
    }

然后在ideonBackPressed()函数中，您可以执行以下操作：

@Override
public void onBackPressed() {

 if (currentFragmentShown == JOBS_FRAGMENT) {
        //Do whatever you want to do when jobs fragment is shown
    } else {
        //Do whatever you want to do when shippement out fragment fragment is shown
    }
}

这也许不是最好的解决方案，但我希望这能有所帮助