android - 处理 "cannot find symbol class"错误

Question

我正在向Big Nerd Ranch学习，代码和书上的一样 错误发生在 CrimeActivity 类中，我在其中调用 new CrimeFragment()。 我已经导入了支持库，但它仍然存在。还有其他方法可以处理 fragment 吗？

提前谢谢您!!

CrimeActivity 类 -->

package com.example.shivam.criminalintent;

import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentActivity;
import android.support.v4.app.FragmentManager;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

public class CrimeActivity extends FragmentActivity {

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_crime);

        FragmentManager fm = getSupportFragmentManager();
        Fragment fragment = fm.findFragmentById(R.id.fragment_container);
        if (fragment == null) {
            fragment = new CrimeFragment();  // error
            fm.beginTransaction()
                    .add(R.id.fragment_container, fragment)
                    .commit();
        }
    }

}

CrimeFragment 类-->

import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.text.Editable;
import android.text.TextWatcher;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.EditText;

import com.example.shivam.criminalintent.R;

public class CrimeFragment extends Fragment {
     private Crime mCrime;
     private EditText mTitleField;

         @Override
         public  void  onCreate(Bundle saveInstanceState){
         super.onCreate(saveInstanceState);
         mCrime = new Crime();
     }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState){
        View v = inflater.inflate(R.layout.fragment_crime,container,false);
        mTitleField = (EditText) v.findViewById(R.id.crime_title);
        mTitleField.addTextChangedListener(new TextWatcher() {
            @Override
            public void beforeTextChanged(CharSequence charSequence, int i, int i1, int i2) {

            }

            @Override
            public void onTextChanged(CharSequence charSequence, int i, int i1, int i2) {
                mCrime.setTitle(charSequence.toString());
            }

            @Override
            public void afterTextChanged(Editable editable) {

            }
        });
        return v;
    }
}

Answer 1

您正在通过 id 查找 fragment ，该 id 应该是您的 fragment 布局 id，而不是容器 id。

Fragment fragment = fm.findFragmentById(R.id.fragment_container);

替换为:

Fragment fragment = fm.findFragmentById(R.id.your_fragment_id);