不断返回nullpointer异常

Question

我目前正在学习明确的意图。并且我决定要有点创造力，并为三种活动创建明确的意图。 MainActivity，activity2和activity3。在activity1中，我希望能够填写名字和姓氏，然后在我单击提交时，全名将显示在activity2的第一个文本视图中。然后在activity2中有一个按钮，上面写着“单击此处输入出生日期”，然后将其带到activity3中，我应该在其中输入出生日期并点击Submit。点击提交时，出生日期将在全名textview之后的第二个textview中显示。

相反，它会继续停止并返回nullpointer异常

这是MainActivity中编写的代码：

   EditText etFirst, etSecond;
Button btnSubmit;

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

    etFirst=findViewById(R.id.etFirst);
    etSecond=findViewById(R.id.etSecond);
    btnSubmit=findViewById(R.id.btnSubmit);

    btnSubmit.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {

            if(etFirst.getText().toString().isEmpty())
            {
                Toast.makeText(MainActivity.this, "Enter First Name!", Toast.LENGTH_SHORT).show();
            }
            else if (etSecond.getText().toString().isEmpty())
            {
                Toast.makeText(MainActivity.this, "Enter Last Name!", Toast.LENGTH_SHORT).show();
            }
            else
            {
                Intent intent= new Intent(MainActivity.this, com.example.nameintent.Activity2.class);
                String first= etFirst.getText().toString().trim();
                String second=etSecond.getText().toString().trim();

                intent.putExtra("first", first);
                intent.putExtra("second",second);
                startActivity(intent);
                MainActivity.this.finish();


            }
        }
    });
}

这是活动2中的代码：

       TextView tvName, tvBirth;
Button btnAct3;
final int ACTIVITY3=3;


@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_2);

    tvName=findViewById(R.id.tvName);
    tvBirth=findViewById(R.id.tvBirth);
    btnAct3=findViewById(R.id.btnAct3);

    tvName.setVisibility(View.GONE);


    String first= getIntent().getStringExtra("first");
    String second= getIntent().getStringExtra("second");

    String full= first +" "+second;

    tvName.setText(full);
    tvName.setVisibility(View.VISIBLE);


    btnAct3.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {

            Intent intent=new Intent(Activity2.this, com.example.nameintent.Activity3.class);
            startActivityForResult(intent,ACTIVITY3);

        }
    });

}



@Override
protected void onActivityResult(int requestCode, int resultCode, @Nullable Intent data) {
    super.onActivityResult(requestCode, resultCode, data);


    if (requestCode==ACTIVITY3)
    {
        if(resultCode==RESULT_OK)
        {

            tvBirth.setText(data.getStringExtra("dob"));

        }
    }
    if (resultCode==RESULT_CANCELED)
    {
        String nDob="No Data Received!";
        tvBirth.setText(nDob);
        tvBirth.setVisibility(View.VISIBLE);
    }
}
}

这是我在Activity3中编写的代码：

         EditText etDob;
Button btnSubmit;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_3);

    etDob=findViewById(R.id.etDob);
    btnSubmit=findViewById(R.id.btnSubmit);

    btnSubmit.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {

            if (etDob.getText().toString().isEmpty())
            {
                Toast.makeText(Activity3.this, "Please Enter Date Of Birth!", Toast.LENGTH_SHORT).show();
            }
            else
            {
                Intent intent=new Intent(Activity3.this, com.example.nameintent.Activity2.class);
                String dob= etDob.getText().toString().trim();
                intent.putExtra("dob",dob);
                setResult(RESULT_OK);
                Activity3.this.finish();
            }
        }
    });

}

空点异常发生在

      tvBirth.setText(data.getStringExtra("dob")); in activity2