我的logcat说它位于我的Register.java中
更具体地说，它说“原因：java.lang.NullPointerException：尝试在com.example上的空对象引用上调用虚拟方法'void android.widget.Button.setOnClickListener（android.view.View $ OnClickListener）”。 quizgame.Register.onCreate（Register.java:32）“
我已附上以下代码。 （第32行是：bRegister.setOnClickListener（this）;
我不知道我想念的是什么。我在单击按钮之前和之后都运行过此代码，效果很好，所以我不明白为什么它不会通过。
package com.example.quizgame;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;
import androidx.appcompat.app.AppCompatActivity;
public class Register extends AppCompatActivity implements View.OnClickListener {
Button bRegister;
EditText etFirstName, etLastName, etDateOfBirth, etEmail, etUsername, etPassword;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_register);
etFirstName = findViewById(R.id.etFirstName);
etLastName = findViewById(R.id.etLastName);
etDateOfBirth = findViewById(R.id.etDateOfBirth);
etEmail = findViewById(R.id.etEmail);
etUsername = findViewById(R.id.etUsername);
etPassword = findViewById(R.id.etPassword);
bRegister = findViewById(R.id.bRegister);
bRegister.setOnClickListener(this);
// below will tell user the edittext fields are empty if nothing is entered
if (etFirstName.length() == 0) {
etFirstName.setError("Enter First Name");
}
if (etLastName.length() == 0) {
etLastName.setError("Enter Last Name");
}
if (etDateOfBirth.length() == 0) {
etDateOfBirth.setError("Enter DOB");
}
if (etUsername.length() == 0) {
etUsername.setError("Enter your username");
}
if (etPassword.length() == 0) {
etPassword.setError("Enter your Password");
}
if (etEmail.length() == 0) {
etEmail.setError("Enter your Email, make sure its in proper format [email protected]");
}
}
@Override
//below FirstName and LastName needs to be more than 3 characters in order for registration button to work
public void onClick(View v) {
String FirstName = etFirstName.getText().toString();
if (FirstName.isEmpty() || FirstName.length() < 3) {
etFirstName.setError("First name can not be less than 3 characters and no more than 30");
} else {
etFirstName.setError(null);
}
{
String LastName = etLastName.getText().toString();
if (LastName.isEmpty() || LastName.length() < 3) {
etLastName.setError("Last Name can not be less than 3 characters and no more than 30");
} else {
etLastName.setError(null);
}
}
//clicking Register button will bring you back to the Login page
switch (v.getId()) {
case R.id.bRegister:
if (etFirstName.length() == 0 && etLastName.length() == 0) {
Toast.makeText(getApplicationContext(), "All Fields Must Be Filled", Toast.LENGTH_SHORT).show();
} else {
startActivity(new Intent(this, MainActivity.class));
break;
}
}
}
}
确定在定义视图侦听器的xml中有此名称吗：
android:onClick="buttonOnClick"
如果没有，请将其添加到xml文件的bRegister视图中。希望这会有所帮助：）