Question

LOGCAT Erorr

java.lang.NullPointerException：尝试调用虚方法   'null上的java.lang.String a.thebook.m_Model.new_book1.getnamebook（）'   对象参考

in java Class

package a.thebook;

import android.content.Intent;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.widget.EditText;
import a.thebook.m_Model.new_book1;
....


public class my_book  extends AppCompatActivity {




    private new_book1 model;
    private EditText  bookname1;



    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.my_book_activity);


        EditText bookname1 = (EditText) findViewById(R.id.editTextbookname2);
         bookname1.setText(model.getbookname());
...



}

从firebase数据库获取值。 new_book1

package a.thebook.m_Model;


import java.util.Objects;


public class new_book1 {


    public String author;
    public String bookname;

    public new_book1() {
    }
    public new_book1(String bookname ,String author) {
        this.bookname = bookname;
        this.author = author;

    }
    public String getauthor(int author) {

        return this.author;
    }
    public String getbookname() {

        return this.bookname;
    }

}

Answer 1

您尚未初始化model变量。因此，您收到null object错误。

初始化您的new_book1变量，您的代码将正常工作

希望这会有所帮助：）

Answer 2

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.my_book_activity);
    model = new new_book1("abc","xyz");

    EditText bookname1 = (EditText) findViewById(R.id.editTextbookname2);
     bookname1.setText(model.getbookname());

}

这会对你有帮助。

Answer 3

使用：

private new_book1 model = new new_book1("myBook", "myself");

我不能在EditText中setText

3 个答案: