如何从活动转移到片段？

Question

单击应用栏上的三个按钮时，我必须在我的主要活动中包含三个片段。现在，问题是我想从第二个活动返回到我正在使用 Intent 的 mainActivity 上的特定片段，但在应用程序开始时意图为 null 并获得 nullpointer 异常和应用程序崩溃。

这里是 MainActivity.java

public class MainActivity extends AppCompatActivity {

private ActivityMainBinding binding;

FragmentTransaction fragmentTransaction;
HomeFragment homeFrag;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    binding = DataBindingUtil.setContentView(this,R.layout.activity_main);

    //--------Set and Get Tool Bar-------//
    setSupportActionBar(binding.appbar);
    getSupportActionBar().setTitle("");

    if(getIntent() !=null){
        String is = getIntent().getStringExtra("check");
        if(is.equals("1")){
            SearchFragment searchFrag = new SearchFragment();
            if(searchFrag != null){
                fragmentTransaction = getSupportFragmentManager().beginTransaction();
                fragmentTransaction.replace(R.id.fragmentContainer, searchFrag)
                        .addToBackStack(null).commit();
            }
        }
    }else{
        homeFrag = new HomeFragment();
        if(homeFrag!=null) {
            fragmentTransaction = getSupportFragmentManager().beginTransaction();
            fragmentTransaction.replace(R.id.fragmentContainer, homeFrag).commit();
        }
    }
}
public void MoveToSearchActivity(View view){
    SearchFragment searchFag = new SearchFragment();

    fragmentTransaction = getSupportFragmentManager().beginTransaction();
    fragmentTransaction.replace(R.id.fragmentContainer,searchFag).commit();
}

public void MoveToHomeActivity(View view){
    if(homeFrag!=null) {
        fragmentTransaction = getSupportFragmentManager().beginTransaction();
        fragmentTransaction.replace(R.id.fragmentContainer, homeFrag).commit();
    }
}

public void MoveToAlertFrag(View view){
    AlertFragment alertFragment = new AlertFragment();

    fragmentTransaction = getSupportFragmentManager().beginTransaction();
    fragmentTransaction.replace(R.id.fragmentContainer,alertFragment).commit();
}

这是我的 FilterActivity.java，我将从中返回片段：

public class FilterActivity extends AppCompatActivity{

private ActivityFilterBinding binding;

@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_filter);

    //--------------Get ToolBar-----------//
    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);
    getSupportActionBar().setTitle(" ");
    getSupportActionBar().setDisplayShowHomeEnabled(true);
    getSupportActionBar().setDisplayHomeAsUpEnabled(true);
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    switch (item.getItemId()){
        case android.R.id.home:
            Intent homeIntent = new Intent(FilterActivity.this, MainActivity.class);
            homeIntent.putExtra("check",1);
            startActivity(homeIntent);
            break;
        default:
            break;
    }
    return true;
}
}

谢谢。

Answer 1

在MainActivity 试试这个，

// Toolbar code
...

int is = -1;
if (getIntent() != null && getIntent().hasExtra("check")) {
    is = getIntent().getIntExtra("check", -1);
}
switch (is) {
    case 1:
        // load SearchFragment
        break;
    case 2:
        // load MoveToAlertFrag
        break;
    default:
        // load HomeFragment
        break;
}