java - 无法从Activity获取值到Fragment，NullPointerException

Question

所以我已经为此工作了几天，但我不断收到 NullPointerException。我有一个 MainActivity、一个 OutputActivity 和一个 OutputFragment。我需要将 MainActivity 中的 editText 中的数据获取到 OutputFragment 中。我可以有意地将其从 MainActivity 获取到 OutputActivity 并将值打印到 logcat，但我无法将其从 OutputActivity 获取到 OutputFragment。

我尝试过:
-使用 bundle 将其从 MainActivity 发送到 OutputFragment
-使用Intent发送到OutputActivity，然后使用Intent发送到OutputFragment
-使用Intent将其发送到OutputActivity，然后使用bundle将其发送到OutputFragment

我一直在 Stack Overflow、Google、观看视频等方面进行搜索。

每次我尝试检索 OutputFragment 中的值时，都会收到 NullPointerException。我是一名大学生，我根本不明白我做错了什么。一切看起来都不错，但我不断遇到异常(exception)。当我尝试不同的东西时，我注释掉了一堆行，所以我为可读性道歉，我认为更多的信息总比更少的信息好，所以我留下了它们。 (整个OutputActivity目前基本都被注释掉了)

有人可以帮助我并告诉我这个愚蠢的错误吗？

谢谢

主要 Activity

package com.murach.josephsmithsemesterproject;

import androidx.annotation.Nullable;
import androidx.appcompat.app.AppCompatActivity;

import android.content.Intent;
import android.os.Bundle;
import android.os.PersistableBundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;

public class MainActivity extends AppCompatActivity {


//Initialize variables
EditText benchPressEditText;
EditText squatEditText;
EditText overheadPressEditText;
EditText deadliftEditText;
Button calculateBtn;



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

    // Get references to the widgets
    benchPressEditText = (EditText) findViewById(R.id.benchPressEditText);
    squatEditText = (EditText) findViewById(R.id.squatEditText);
    overheadPressEditText = (EditText) findViewById(R.id.overheadPressEditText);
    deadliftEditText = (EditText) findViewById(R.id.deadliftEditText);
    calculateBtn = (Button) findViewById(R.id.calculateBtn);



    calculateBtn.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            sendData();
            openOutputActivity();
        }
    });


}



private void openOutputActivity() {
    Intent intent = new Intent(getApplicationContext(), OutputActivity.class);
    startActivity(intent);
}

private void sendData() {
    //Get values from edit text
   String oneRepBench = benchPressEditText.getText().toString();

    OutputFragment outputFragment = new OutputFragment();
    Bundle bundle = new Bundle();
    bundle.putString("oneRepBench",oneRepBench);
    Log.v("Data", oneRepBench);

   //set fragment class arguments

   //outputFragment.setArguments(bundle);

    //Intent intent = new Intent(getApplicationContext(), OutputActivity.class);
    //intent.putExtra("oneRepBench", oneRepBench);
    //startActivity(intent);





}

}

输出 Activity

package com.murach.josephsmithsemesterproject;

import androidx.appcompat.app.AppCompatActivity;

import android.content.Intent;
import android.os.Bundle;
import android.util.Log;

public class OutputActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    //Set the view for the activities XML
    setContentView(R.layout.activity_output);

    //Bundle bundle = getArguments();
    //Log.v("getString", bundle.getString("oneRepBench", "No value"));
    //String oneRepBench = bundle.getString("oneRepBench");

    //Intent intent = getIntent();
    //String oneRepBench = intent.getStringExtra("oneRepBench");
    //Log.v("Data now", oneRepBench);

    //Intent outputIntent = new Intent(getApplicationContext(), OutputFragment.class);
    //intent.putExtra("oneRepbench", oneRepBench);
    //startActivity(intent);

    //Bundle bundle = new Bundle();
    //bundle.putString("oneRepBench", oneRepBench);

    //OutputFragment outputFragment = new OutputFragment();
    //outputFragment.setArguments(bundle);


}

}

输出 fragment

 package com.murach.josephsmithsemesterproject;

    import android.content.Intent;
    import android.os.Bundle;
    import android.util.Log;
    import android.view.LayoutInflater;
    import android.view.View;
    import android.view.ViewGroup;
    import android.widget.EditText;
    import android.widget.TextView;

    import androidx.annotation.NonNull;
    import androidx.annotation.Nullable;
    import androidx.fragment.app.Fragment;

    import org.w3c.dom.Text;

    import java.util.Objects;

    public class OutputFragment extends Fragment {

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

        //Bundle bundle = getArguments();
        //Log.v("getString", bundle.getString("oneRepBench", "No value"));
        //String oneRepBench = bundle.getString("oneRepBench");

        //TextView oneRepBenchText = (TextView) view.findViewById(R.id.oneRepBench);
        //oneRepBenchText.setText(oneRepBench);
        //Intent intent = getActivity().getIntent();
        //String oneRepBench = intent.getStringExtra("oneRepBench");
    }*/

    @Override
    public View onCreateView(LayoutInflater inflater,ViewGroup container, Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.fragment_output, container, false);

        //assert getArguments() != null;
        //String oneRepBench = getArguments().getString("oneRepBench");
        //Intent intent = getActivity().getIntent();
        //String oneRepBench = intent.getStringExtra("oneRepBench");
        //Log.v("Data now", oneRepBench);

        String text;
        text = this.getArguments().getString("oneRepBench");
        //Returns NullPointerException

        return view;
    }

}

Answer 1

尝试使用此代码将数据从 Activity 传递到 fragment

在Activity中添加fragment

   Bundle bundle = new Bundle();
   bundle.putString("edttext", "value");
     // set Fragmentclass Arguments
    Fragmentclass fragobj = new Fragmentclass();
    fragobj.setArguments(bundle);
    FragmentManager manager = getFragmentManager();
    FragmentTransaction transaction = manager.beginTransaction();
    transaction.add(R.id.container,fragobj,YOUR_FRAGMENT_STRING_TAG);
    transaction.addToBackStack(null);
    transaction.commit();

在 fragment 中

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
        Bundle savedInstanceState) {
     Bundle bundle= getArguments();
      if(bundle!=null){
         String strtext = bundle.getString("value"); 
       }

    return inflater.inflate(R.layout.fragment, container, false);
}