"java.lang.NullPointerException。试图在一个空对象上调用虚拟方法'android.text.Editable android.widget.EditText.getText()'..."

Question

我做了一个代码来添加剩余的天数，但它显示一些关闭我的代码是错误的，我是新的Android Studio。

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我还上传了logcat错误，请点击这里。

日志猫

[AddRemainDaysActivity.java]

import android.content.Intent;
import android.os.Bundle;
import android.text.TextUtils;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ListView;
import android.widget.TextView;
import android.widget.Toast;

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

import com.google.firebase.database.DatabaseReference;
import com.google.firebase.database.FirebaseDatabase;

public class AddRemainDaysActivity extends AppCompatActivity {

    TextView textviewAsgName;
    EditText editTextRemaindDays;
    Button buttonAdd;

    ListView listViewRemainDays;

    DatabaseReference databaseRemainDays;

    @Override
    protected void onCreate(Bundle saveInstanceState) {
        super.onCreate(saveInstanceState);
        setContentView(R.layout.add_remain_days);

        textviewAsgName = (TextView) findViewById(R.id.textViewAsgName);
        editTextRemaindDays = (EditText) findViewById(R.id.editTextRemaindDays);
        buttonAdd = (Button) findViewById(R.id.buttonAdd);

        listViewRemainDays = (ListView) findViewById(R.id.listViewRemainDays);

        Intent intent = getIntent();

        String id = intent.getStringExtra(MainActivity.ASSIGNMENT_ID);
        String topic = intent.getStringExtra(MainActivity.ASSIGNMENT_TOPIC);

        textviewAsgName.setText(topic);

        databaseRemainDays = FirebaseDatabase.getInstance().getReference("remainDays").child(id);

        buttonAdd.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                saveremainDays();
            }
        });

        }
    private void saveremainDays(){
        String remainDaysname = editTextRemaindDays.getText().toString().trim();

        if(!TextUtils.isEmpty(remainDaysname)) {
            String id = databaseRemainDays.push().getKey();

            remainDays RemainDays = new remainDays(id, remainDaysname);

            databaseRemainDays.child(id).setValue(RemainDays);

            Toast.makeText(this,"Remain days added :)", Toast.LENGTH_LONG).show();
        }else{
            Toast.makeText(this, "You must insert remaining days to proceed!", Toast.LENGTH_LONG).show();
        }
    }
}````

[retainDays.java]

包 com.example.as3;

public class remainDays {

private String remainDaysID;
private String remainDaysname;

public remainDays() {

}

public remainDays(String remainDaysID, String remainDaysname) {
    this.remainDaysID = remainDaysID;
    this.remainDaysname = remainDaysname;
}

public String getRemainDaysID() {
    return remainDaysID;
}

public String getRemainDaysname() {
    return remainDaysname;
}

}````

这是XML文件。

[add_remain_days_xml]

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/Activity_add_remaindays"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context=".AddRemainDaysActivity">

    <TextView
        android:id="@+id/textViewAsgName"
        android:textAppearance="@style/TextAppearance.AppCompat.Large"
        android:textAlignment="center"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:gravity="center" />

    <EditText
        android:id="@+id/editTextRemainDays"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:ems="10"
        android:hint="Enter remaining days"
        android:inputType="textPersonName"
        android:layout_marginTop="20dp"/>

    <Button
        android:id="@+id/buttonAdd"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginTop="22dp"
        android:text="Add" />

    <TextView
        android:id="@+id/textView"
        android:textAppearance="@style/TextAppearance.AppCompat.Large"
        android:textAlignment="center"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:gravity="center"
        android:text="Assignment"/>

    <ListView
        android:id="@+id/listViewRemainDays"
        android:layout_width="match_parent"
        android:layout_height="match_parent"/>

</LinearLayout>````

Answer 1

你的 editTextRemaindDays 视图没有被初始化，这就是为什么它抛出NullPointerException的原因。当我看到你的导入时，你没有像这样导入你的资源文件。

import youPackage.R;

请检查你是否正确访问了 editTextRemaindDays 恰如其分 editTextRemaindDays 你在xml文件中给出的任何东西，因为你没有附上你的xml，所以我看不到你给出的ID。