java - 无法解析每个 Activity 的符号 'R'

Question

这个问题已经有答案了:

"cannot resolve symbol R" in Android Studio (101 个回答)

已关闭 6 年前。

我制作了一个小应用程序，其操作可以调用两个 fragment 。即使 android studio 标记每个 findViewById(R.id.Example) 读取，这也绝对可以正常工作，这显然意味着有问题。只有“R”标记为红色。但我不明白出了什么问题？特别是当应用程序运行正常并且编译没有给出任何错误时。

这是主要 Activity :

package silverbeach.meintieralter;

import android.app.Fragment;
import android.app.FragmentTransaction;
import android.os.Bundle;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.support.v4.app.FragmentActivity;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.View;
import android.view.Menu;
import android.view.MenuItem;

public class MainActivity extends AppCompatActivity {

    private FragmentOne fragmentOne;
    private FragmentTwo fragmentTwo;



    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);



        //Fragmente ankündigen
        fragmentOne = (FragmentOne) Fragment.instantiate(this, FragmentOne.class.getName(),null);
        fragmentTwo = (FragmentTwo) Fragment.instantiate(this, FragmentTwo.class.getName(),null);


        //Fragment 1 wird STANDARTMÄSSIG eingeblendet und ausgeführt
        FragmentTransaction fragmentTransaction = getFragmentManager().beginTransaction();
        fragmentTransaction.add(R.id.flFragmentContainer, fragmentOne);
        fragmentTransaction.commit();



    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.menu_main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {

        switch (item.getItemId()){
            case R.id.action_one:{
                FragmentTransaction fragmentTransaction = getFragmentManager().beginTransaction();
                fragmentTransaction.replace(R.id.flFragmentContainer, fragmentOne);
                fragmentTransaction.commit();
                break;
            }
            case R.id.action_two:{
                FragmentTransaction fragmentTransaction = getFragmentManager().beginTransaction();
                fragmentTransaction.replace(R.id.flFragmentContainer, fragmentTwo);
                fragmentTransaction.commit();
                break;
            }
            default:{

            }
        }

        return super.onOptionsItemSelected(item);
    }
}

这是其中一个 fragment :

package silverbeach.meintieralter;

import android.app.Fragment;
import android.content.Context;
import android.os.Bundle;
import android.os.Vibrator;
import android.support.annotation.Nullable;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Spinner;
import android.widget.TextView;
import android.view.View.OnClickListener;

import static android.content.Context.VIBRATOR_SERVICE;


public class FragmentOne extends Fragment {

    private TextView out;
    private EditText alter;
    private Spinner s;
    private Button button;
    private FloatingActionButton fab;



    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);




    }

    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {

        View layout = inflater.inflate(R.layout.fragment_one, null);

        out = (TextView) layout.findViewById(R.id.out);
        alter = (EditText) layout.findViewById(R.id.altereingabe);
        s = (Spinner) layout.findViewById(R.id.spinner);
        button = (Button) layout.findViewById(R.id.button);
        fab = (FloatingActionButton) layout.findViewById(R.id.fab);



        FloatingActionButton fab = (FloatingActionButton) layout.findViewById(R.id.fab);
        fab.setOnClickListener(new View.OnClickListener()
        {
                                      @Override
                                      public void onClick(View v) {




                                          String text = s.getSelectedItem().toString();
                                          int newage = 404;
                                          double doublenewage = 4.04;
                                          double doubleage;
                                          int intage;
                                          doubleage = Double.parseDouble(alter.getText().toString());
                                          intage = (int) doubleage;

                                          switch (text) {
                                              case "Katze": {
                                                  switch (intage) {

                                                      default:
                                                          Snackbar.make(v, "Leider schon tot.", Snackbar.LENGTH_LONG).show();
                                                          out.setText("Leider schon tot.");
                                                          break;


                                                  }
                                                  if (intage <= 119)
                                                      Snackbar.make(v, "Du bist eine " + Integer.toString(newage) + " Jahre alte Katze.", Snackbar.LENGTH_LONG).show();

                                                  else {
                                                      double deadagecat;
                                                      deadagecat = intage * 0.283;
                                                      long dc = Math.round(deadagecat);
                                                      Snackbar.make(v, "Du bist höchstwahrscheinlich schon tot, aber theoretisch wärst du eine " + dc + "-Jährige Katze.", Snackbar.LENGTH_LONG).show();


                                                  }


                                              }break;
                                              case "Pferd": {
                                                  doublenewage = intage / 3.1;
                                                  long longpferdage = Math.round(doublenewage);
                                                  newage = (int) longpferdage;

                                                  if (newage < 31)
                                                      Snackbar.make(v, "Du bist ein " + Integer.toString(newage) + " Jahre altes Pferd", Snackbar.LENGTH_LONG).show();

                                                  else
                                                      Snackbar.make(v, "Du bist höchstwahrscheinlich schon tot, aber theoretisch wärst du ein " + newage + "-Jähriges Pferd.", Snackbar.LENGTH_LONG).show();

                                              }break;
                                              case "Hund": {
                                                  newage = intage / 7;
                                                  if (newage < 15)
                                                      Snackbar.make(v, "Du bist ein " + Integer.toString(newage) + " Jahre alter Hund.", Snackbar.LENGTH_LONG).show();

                                                  else
                                                      Snackbar.make(v, "Du bist höchstwahrscheinlich schon tot, aber theoretisch wärst du ein " + newage + "-Jähriger Hund.", Snackbar.LENGTH_LONG).show();


                                              }break;
                                              case "Meerschweinchen": {
                                                  newage = intage / 12;
                                                  if (newage < 8)

                                                      //out.setText("Du bist ein " + Integer.toString(newage) + " Jahre altes Meerie.");
                                                      Snackbar.make(v, "Du bist ein "+Integer.toString(newage)+" Jahre altes Meerie.", Snackbar.LENGTH_LONG).show();






                                                  else{
                                                  Snackbar.make(v, "Du bist höchstwahrscheinlich schon tot, aber theoretisch wärst du ein " + newage + "-Jähriges Meerie.", Snackbar.LENGTH_LONG).show();}


                                              }break;


                                          }



                                      }


                                  });
        // tvText1 = (TextView) layout.findViewById(R.id.tvFragmentOne);





        return layout;
    }





    @Override
    public void onActivityCreated(Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);

        //tvText1.setText("Ok View 1 wurde geändert.");

    }
}

Answer 1

您只需重建并清理您的项目即可。这只是 IDE 本身的构建问题。对其进行构建、清理，然后就可以开始了。希望这有帮助