Java Android Studio中单击侦听器中的意图引发错误
大家好,我正试图在一个点击监听器中将屏幕从MainActivity类更改为UserLogin类,下面是我的代码Java Android Studio中单击侦听器中的意图引发错误,java,android,android-studio,android-intent,Java,Android,Android Studio,Android Intent,大家好,我正试图在一个点击监听器中将屏幕从MainActivity类更改为UserLogin类,下面是我的代码 package com.example.user.appproject; import android.app.ProgressDialog; import android.content.Intent; import android.os.Bundle; import android.support.v7.app.AppCompatActivity; import android.
package com.example.user.appproject;
import android.app.ProgressDialog;
import android.content.Intent;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import com.android.volley.AuthFailureError;
import com.android.volley.Request;
import com.android.volley.RequestQueue;
import com.android.volley.Response;
import com.android.volley.VolleyError;
import com.android.volley.toolbox.StringRequest;
import com.android.volley.toolbox.Volley;
import java.util.HashMap;
import java.util.Map;
public class MainActivity extends AppCompatActivity {
ProgressDialog progressDoalog;
EditText firstname, lastname, age,email;
Button insert, show;
RequestQueue requestQueue;
String insertUrl = "http://192.168.1.11/insertRecord.php";
String showUrl = "http://192.168.1.11/showStudents.php";
TextView result;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
firstname = (EditText) findViewById(R.id.edtFirstname);
lastname = (EditText) findViewById(R.id.edtLastname);
age = (EditText) findViewById(R.id.edtAge);
insert = (Button) findViewById(R.id.insert);
email=(EditText) findViewById(R.id.edtEmail);
requestQueue = Volley.newRequestQueue(getApplicationContext());
insert.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
StringRequest request = new StringRequest(Request.Method.POST, insertUrl, new Response.Listener<String>() {
@Override
public void onResponse(String response) {
System.out.println(response.toString());
}
}, new Response.ErrorListener() {
@Override
public void onErrorResponse(VolleyError error) {
}
}) {
@Override
protected Map<String, String> getParams() throws AuthFailureError {
Map<String,String> parameters = new HashMap<String, String>();
parameters.put("firstname",firstname.getText().toString());
parameters.put("lastname",lastname.getText().toString());
parameters.put("email",email.getText().toString());
parameters.put("age",age.getText().toString());
return parameters;
}
};
requestQueue.add(request);
Intent intent = new Intent(MainActivity.this,UserLogin.class);
startActivity(intent);
}
});
}
}
我不明白空对象引用可能在哪里,就好像我取出了意图代码一切正常一样,我的userLogin类在清单文件中定义了。
下面是下面代码的xml代码
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
android:id="@+id/main">
<EditText
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:inputType="textPersonName"
android:text="firstname"
android:ems="10"
android:id="@+id/edtFirstname"
android:layout_alignParentTop="true"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true"
android:layout_alignParentRight="true"
android:layout_alignParentEnd="true" />
<EditText
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:inputType="textPersonName"
android:text="lastname"
android:ems="10"
android:id="@+id/edtLastname"
android:layout_below="@+id/edtFirstname"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true"
android:layout_alignParentRight="true"
android:layout_alignParentEnd="true" />
<EditText
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:inputType="textPersonName"
android:text="email"
android:ems="10"
android:id="@+id/edtEmail"
android:layout_below="@+id/edtLastname"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true"
android:layout_alignParentRight="true"
android:layout_alignParentEnd="true" />
<EditText
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:inputType="textPersonName"
android:text="age"
android:ems="10"
android:id="@+id/edtAge"
android:layout_below="@+id/edtEmail"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true"
android:layout_alignParentRight="true"
android:layout_alignParentEnd="true" />
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="INSERT STUDENT"
android:id="@+id/insert"
android:layout_marginBottom="138dp"
android:layout_alignParentBottom="true"
android:layout_centerHorizontal="true" />
</RelativeLayout>
任何帮助都将不胜感激
用户登录的主要代码:
import android.app.ProgressDialog;
import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.text.TextUtils;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;
import com.android.volley.Request;
import com.android.volley.RequestQueue;
import com.android.volley.Response;
import com.android.volley.VolleyError;
import com.android.volley.toolbox.StringRequest;
import com.android.volley.toolbox.Volley;
import java.util.HashMap;
import java.util.Map;
public class UserLogin extends AppCompatActivity {
// Creating EditText.
EditText Email, Password;
// Creating button;
Button LoginButton;
// Creating Volley RequestQueue.
RequestQueue requestQueue;
// Create string variable to hold the EditText Value.
String EmailHolder, PasswordHolder;
// Creating Progress dialog.
ProgressDialog progressDialog;
// Storing server url into String variable.
String HttpUrl = "https://192.168.1.11/userLogin.php";
Boolean CheckEditText;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
// Assigning ID's to EditText.
Email = (EditText) findViewById(R.id.editText_Email);
Password = (EditText) findViewById(R.id.editText_Password);
// Assigning ID's to Button.
LoginButton = (Button) findViewById(R.id.button_login);
// Creating Volley newRequestQueue .
requestQueue = Volley.newRequestQueue(UserLogin.this);
// Assigning Activity this to progress dialog.
progressDialog = new ProgressDialog(UserLogin.this);
// Adding click listener to button.
LoginButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
CheckEditTextIsEmptyOrNot();
if (CheckEditText) {
UserLogin();
} else {
Toast.makeText(UserLogin.this, "Please fill all form fields.", Toast.LENGTH_LONG).show();
}
}
});
}
// Creating user login function.
public void UserLogin() {
// Showing progress dialog at user registration time.
progressDialog.setMessage("Please Wait");
progressDialog.show();
// Creating string request with post method.
StringRequest stringRequest = new StringRequest(Request.Method.POST, HttpUrl,
new Response.Listener<String>() {
@Override
public void onResponse(String ServerResponse) {
// Hiding the progress dialog after all task complete.
progressDialog.dismiss();
// Matching server responce message to our text.
if(ServerResponse.equalsIgnoreCase("Data Matched")) {
// If response matched then show the toast.
Toast.makeText(UserLogin.this, "Logged In Successfully", Toast.LENGTH_LONG).show();
// Finish the current Login activity.
finish();
}
else {
// Showing Echo Response Message Coming From Server.
Toast.makeText(UserLogin.this, ServerResponse, Toast.LENGTH_LONG).show();
}
}
},
new Response.ErrorListener() {
@Override
public void onErrorResponse(VolleyError volleyError) {
// Hiding the progress dialog after all task complete.
progressDialog.dismiss();
// Showing error message if something goes wrong.
Toast.makeText(UserLogin.this, volleyError.toString(), Toast.LENGTH_LONG).show();
}
}) {
@Override
protected Map<String, String> getParams() {
// Creating Map String Params.
Map<String, String> params = new HashMap<String, String>();
// Adding All values to Params.
// The firs argument should be same sa your MySQL database table columns.
params.put("User_Email", EmailHolder);
params.put("User_Password", PasswordHolder);
return params;
}
};
// Creating RequestQueue.
RequestQueue requestQueue = Volley.newRequestQueue(UserLogin.this);
// Adding the StringRequest object into requestQueue.
requestQueue.add(stringRequest);
}
public void CheckEditTextIsEmptyOrNot() {
// Getting values from EditText.
EmailHolder = Email.getText().toString().trim();
PasswordHolder = Password.getText().toString().trim();
// Checking whether EditText value is empty or not.
if (TextUtils.isEmpty(EmailHolder) || TextUtils.isEmpty(PasswordHolder)) {
// If any of EditText is empty then set variable value as False.
CheckEditText = false;
} else {
// If any of EditText is filled then set variable value as True.
CheckEditText = true;
}
}
}
导入android.app.ProgressDialog;
导入android.content.Intent;
导入android.support.v7.app.AppActivity;
导入android.os.Bundle;
导入android.text.TextUtils;
导入android.view.view;
导入android.widget.Button;
导入android.widget.EditText;
导入android.widget.Toast;
导入com.android.volley.Request;
导入com.android.volley.RequestQueue;
导入com.android.volley.Response;
导入com.android.volley.VolleyError;
导入com.android.volley.toolbox.StringRequest;
导入com.android.volley.toolbox.volley;
导入java.util.HashMap;
导入java.util.Map;
公共类UserLogin扩展了AppCompatActivity{
//创建编辑文本。
编辑文本电子邮件、密码;
//创建按钮;
按钮登录按钮;
//创建截击请求队列。
请求队列请求队列;
//创建字符串变量以保存EditText值。
字符串持有者,密码持有者;
//创建进度对话框。
进行对话进行对话;
//将服务器url存储到字符串变量中。
字符串HttpUrl=”https://192.168.1.11/userLogin.php";
布尔校验文本;
@凌驾
创建时受保护的void(Bundle savedInstanceState){
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
//将ID分配给EditText。
Email=(EditText)findviewbyd(R.id.EditText\u Email);
密码=(EditText)findViewById(R.id.EditText\u密码);
//为按钮分配ID。
LoginButton=(按钮)findViewById(R.id.Button\u登录);
//创建截击newRequestQueue。
requestQueue=Volley.newRequestQueue(UserLogin.this);
//将此活动分配给“进度”对话框。
progressDialog=新建progressDialog(UserLogin.this);
//添加click listener到按钮。
LoginButton.setOnClickListener(新视图.OnClickListener(){
@凌驾
公共void onClick(视图){
CheckEditTextIsEmptyOrNot();
如果(检查编辑文本){
UserLogin();
}否则{
Toast.makeText(UserLogin.this,“请填写所有表单字段”,Toast.LENGTH_LONG.show();
}
}
});
}
//创建用户登录功能。
public void UserLogin(){
//在用户注册时显示进度对话框。
progressDialog.setMessage(“请稍候”);
progressDialog.show();
//使用post方法创建字符串请求。
StringRequest StringRequest=新的StringRequest(Request.Method.POST,HttpUrl,
新的Response.Listener(){
@凌驾
公共void onResponse(字符串ServerResponse){
//在所有任务完成后隐藏进度对话框。
progressDialog.disclose();
//将服务器响应消息与文本匹配。
if(ServerResponse.equalsIgnoreCase(“数据匹配”)){
//如果回答一致,则展示祝酒词。
Toast.makeText(UserLogin.this,“成功登录”,Toast.LENGTH_LONG.show();
//完成当前登录活动。
完成();
}
否则{
//显示来自服务器的回显响应消息。
Toast.makeText(UserLogin.this、ServerResponse、Toast.LENGTH_LONG.show();
}
}
},
新的Response.ErrorListener(){
@凌驾
公共错误响应(截击错误截击错误){
//在所有任务完成后隐藏进度对话框。
progressDialog.disclose();
//如果出现错误,则显示错误消息。
Toast.makeText(UserLogin.this,volleyError.toString(),Toast.LENGTH_LONG.show();
}
}) {
@凌驾
受保护的映射getParams(){
//正在创建映射字符串参数。
Map params=新的HashMap();
//将所有值添加到参数。
//第一个参数应该与MySQL数据库表列相同。
参数put(“用户电子邮件”,EmailHolder);
参数put(“用户密码”,密码持有者);
返回参数;
}
};
//正在创建请求队列。
RequestQueue RequestQueue=Volley.newRequestQueue(UserLogin.this);
//将StringRequest对象添加到requestQueue中。
添加(stringRequest);
}
公共无效CheckEditTextIsEmptyOrNot(){
//从EditText获取值。
EmailHolder=Email.getText().toString().trim();
PasswordHolder=Password.getText().toString().trim();
//检查EditText值是否为空。
if(TextUtils.isEmpty(EmailHolder)| | TextUtils.isEmpty(PasswordHolder)){
//如果任何EditText为空,则将变量值设置为False。
CheckEditText=false;
}否则{
//如果任何EditText已填充,则将变量值设置为True。
检查编辑文本=
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
android:id="@+id/main">
<EditText
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:inputType="textPersonName"
android:text="firstname"
android:ems="10"
android:id="@+id/edtFirstname"
android:layout_alignParentTop="true"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true"
android:layout_alignParentRight="true"
android:layout_alignParentEnd="true" />
<EditText
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:inputType="textPersonName"
android:text="lastname"
android:ems="10"
android:id="@+id/edtLastname"
android:layout_below="@+id/edtFirstname"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true"
android:layout_alignParentRight="true"
android:layout_alignParentEnd="true" />
<EditText
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:inputType="textPersonName"
android:text="email"
android:ems="10"
android:id="@+id/edtEmail"
android:layout_below="@+id/edtLastname"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true"
android:layout_alignParentRight="true"
android:layout_alignParentEnd="true" />
<EditText
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:inputType="textPersonName"
android:text="age"
android:ems="10"
android:id="@+id/edtAge"
android:layout_below="@+id/edtEmail"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true"
android:layout_alignParentRight="true"
android:layout_alignParentEnd="true" />
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="INSERT STUDENT"
android:id="@+id/insert"
android:layout_marginBottom="138dp"
android:layout_alignParentBottom="true"
android:layout_centerHorizontal="true" />
</RelativeLayout>
import android.app.ProgressDialog;
import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.text.TextUtils;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;
import com.android.volley.Request;
import com.android.volley.RequestQueue;
import com.android.volley.Response;
import com.android.volley.VolleyError;
import com.android.volley.toolbox.StringRequest;
import com.android.volley.toolbox.Volley;
import java.util.HashMap;
import java.util.Map;
public class UserLogin extends AppCompatActivity {
// Creating EditText.
EditText Email, Password;
// Creating button;
Button LoginButton;
// Creating Volley RequestQueue.
RequestQueue requestQueue;
// Create string variable to hold the EditText Value.
String EmailHolder, PasswordHolder;
// Creating Progress dialog.
ProgressDialog progressDialog;
// Storing server url into String variable.
String HttpUrl = "https://192.168.1.11/userLogin.php";
Boolean CheckEditText;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
// Assigning ID's to EditText.
Email = (EditText) findViewById(R.id.editText_Email);
Password = (EditText) findViewById(R.id.editText_Password);
// Assigning ID's to Button.
LoginButton = (Button) findViewById(R.id.button_login);
// Creating Volley newRequestQueue .
requestQueue = Volley.newRequestQueue(UserLogin.this);
// Assigning Activity this to progress dialog.
progressDialog = new ProgressDialog(UserLogin.this);
// Adding click listener to button.
LoginButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
CheckEditTextIsEmptyOrNot();
if (CheckEditText) {
UserLogin();
} else {
Toast.makeText(UserLogin.this, "Please fill all form fields.", Toast.LENGTH_LONG).show();
}
}
});
}
// Creating user login function.
public void UserLogin() {
// Showing progress dialog at user registration time.
progressDialog.setMessage("Please Wait");
progressDialog.show();
// Creating string request with post method.
StringRequest stringRequest = new StringRequest(Request.Method.POST, HttpUrl,
new Response.Listener<String>() {
@Override
public void onResponse(String ServerResponse) {
// Hiding the progress dialog after all task complete.
progressDialog.dismiss();
// Matching server responce message to our text.
if(ServerResponse.equalsIgnoreCase("Data Matched")) {
// If response matched then show the toast.
Toast.makeText(UserLogin.this, "Logged In Successfully", Toast.LENGTH_LONG).show();
// Finish the current Login activity.
finish();
}
else {
// Showing Echo Response Message Coming From Server.
Toast.makeText(UserLogin.this, ServerResponse, Toast.LENGTH_LONG).show();
}
}
},
new Response.ErrorListener() {
@Override
public void onErrorResponse(VolleyError volleyError) {
// Hiding the progress dialog after all task complete.
progressDialog.dismiss();
// Showing error message if something goes wrong.
Toast.makeText(UserLogin.this, volleyError.toString(), Toast.LENGTH_LONG).show();
}
}) {
@Override
protected Map<String, String> getParams() {
// Creating Map String Params.
Map<String, String> params = new HashMap<String, String>();
// Adding All values to Params.
// The firs argument should be same sa your MySQL database table columns.
params.put("User_Email", EmailHolder);
params.put("User_Password", PasswordHolder);
return params;
}
};
// Creating RequestQueue.
RequestQueue requestQueue = Volley.newRequestQueue(UserLogin.this);
// Adding the StringRequest object into requestQueue.
requestQueue.add(stringRequest);
}
public void CheckEditTextIsEmptyOrNot() {
// Getting values from EditText.
EmailHolder = Email.getText().toString().trim();
PasswordHolder = Password.getText().toString().trim();
// Checking whether EditText value is empty or not.
if (TextUtils.isEmpty(EmailHolder) || TextUtils.isEmpty(PasswordHolder)) {
// If any of EditText is empty then set variable value as False.
CheckEditText = false;
} else {
// If any of EditText is filled then set variable value as True.
CheckEditText = true;
}
}
}
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_margin="15dp"
tools:context="com.example.user.appproject.UserLogin">
<TextView
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:id="@+id/textView"
android:textSize="20dp"
android:textStyle="bold"
android:text="Volley User Login System"
android:gravity="center"
android:layout_marginTop="20dp"/>
<EditText
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:hint="Enter Your Email"
android:gravity="center"
android:id="@+id/editText_Email"
android:layout_below="@+id/textView"
android:layout_marginTop="20dp"/>
<EditText
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:hint="Enter Your Password"
android:gravity="center"
android:id="@+id/editText_Password"
android:inputType="textPassword"
android:layout_below="@+id/editText_Email"
android:layout_marginTop="20dp"/>
<Button
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="CLICK HERE TO LOGIN"
android:id="@+id/button_login"
android:layout_below="@id/editText_Password"
android:layout_marginTop="20dp"/>
</RelativeLayout>