Android导航抽屉片段

Question

I am working on an Android application that implements a NavigationDrawer.

The NavigationDrawer works fine, so do the fragments transitions but I can't access the Fragment's elements.

Here there is my drawer onItemClick() listener's code:

ConfigureFragment configure = new ConfigureFragment();
Button bt;
InFragment in = new InFragment();
OutFragment out = new OutFragment();
ConditioningFragment cond = new ConditioningFragment();
private String lft = null;
@Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
    selectItem(position);
    android.app.FragmentManager fragmentManager = getFragmentManager();
    FragmentTransaction transaction = fragmentManager.beginTransaction();
    switch(position){
        case 0:
            if(lft == null){
            transaction.replace(R.id.mainContent,configure,"ConfigureFragment");
            transaction.commit();
            lft = "ConfigureFragment";
            }else{
                transaction.replace(fragmentManager.findFragmentByTag(lft).getId(),configure,"ConfigureFragment");
                transaction.commit();
                lft = "ConfigureFragment";
            }
        bt = (Button)configure.getView().findViewById(R.id.configure_bt); //throws NullPointerException
        break;
        case 1:
            if(lft == null){
                transaction.replace(R.id.mainContent,in,"InFragment");
                transaction.commit();
                lft = "InFragment";
            }else{
                transaction.replace(fragmentManager.findFragmentByTag(lft).getId(),in,"InFragment");
                transaction.commit();
                lft = "InFragment";
            }
            break;
        case 2:
            if(lft == null){
                transaction.replace(R.id.mainContent,out,"OutFragment");
                transaction.commit();
                lft = "OutFragment";
            }else{
                transaction.replace(fragmentManager.findFragmentByTag(lft).getId(),out,"OutFragment");
                transaction.commit();
                lft = "OutFragment";
            }
            break;
    }
    drawerLayout.closeDrawer(Gravity.LEFT);
}

Answer 1

String variables don't work with operators like, == . You need to use:

stringVariableOne.equals(stringVariableTwo);

In order to check if the value of one String variable( stringVariableOne , in this case) is equal to another String variable or null ( stringVariableTwo , in this case).

Example:

lft.equals(null);