android-studio - java.lang.RuntimeException:无法启动事件ComponentInfo和调用Android Studio中的另一个事件

Question

我是Android开发的新手，试图创建一个简单的注册应用程序，但是每次单击“在此处注册TextView”时，应用程序都会崩溃。除此之外，我对登录按钮进行了编码以尝试调用另一个 Activity ，但是单击该按钮后它没有响应。我非常努力地发现错误，但是我不确定在编码中错过了什么。

这是主要 Activity

package com.fyp4201.universityguide;

import android.content.Intent;
import android.os.Bundle;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.View;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.TabHost;

public class MainActivity extends AppCompatActivity {
TabHost tabHost;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);

    TabHost host = (TabHost) findViewById(R.id.tabHost);
    host.setup();

    //Tab 1
    TabHost.TabSpec spec = host.newTabSpec("tab1");
    spec.setContent(R.id.tab1);
    spec.setIndicator("Home");
    host.addTab(spec);

    //Tab 2
    spec = host.newTabSpec("tab2");
    spec.setContent(R.id.tab2);
    spec.setIndicator("Search Courses");
    host.addTab(spec);

    //Tab 3
    spec = host.newTabSpec("tab3");
    spec.setContent(R.id.tab3);
    spec.setIndicator("Search University");
    host.addTab(spec);

    //Tab4
    spec = host.newTabSpec("tab4");
    spec.setContent(R.id.tab4);
    spec.setIndicator("Compare Universities");
    host.addTab(spec);

    //Tab5
    spec = host.newTabSpec("tab5");
    spec.setContent(R.id.tab5);
    spec.setIndicator("Ranking of Universities");
    host.addTab(spec);


    FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
    fab.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
                    .setAction("Action", null).show();
        }
    });

}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.menu_main, menu);
    return true;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // Handle action bar item clicks here. The action bar will
    // automatically handle clicks on the Home/Up button, so long
    // as you specify a parent activity in AndroidManifest.xml.
   switch( item.getItemId()){

    //noinspection SimplifiableIfStatement
       case R.id.action_settings: {
        return true;
    }
       case R.id.action_login:{
       Intent intent= new Intent(getApplicationContext(),LoginActivity.class);
       startActivity(intent);
   }
       default:
    return super.onOptionsItemSelected(item);
}
}}

这是登录 Activity 的代码

package com.fyp4201.universityguide;

import android.content.Intent;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;

import android.view.View;
import android.widget.Button;
import android.widget.TextView;

public class LoginActivity extends AppCompatActivity {

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_login2);
    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);

    TextView regis = (TextView) findViewById(R.id.register);
    Button login = (Button) findViewById(R.id.login);

login.setOnClickListener(new View.OnClickListener() {

    @Override
    public void onClick(View v) {
        Intent intent = new Intent(getApplicationContext(), Homeafterlogin.class);
        LoginActivity.this.startActivity(intent);
    }
});


regis.setOnClickListener(new View.OnClickListener() {

    @Override
    public void onClick(View v) {
        Intent intent = new Intent(LoginActivity.this, Register.class);
        LoginActivity.this.startActivity(intent);
    }
});

}}

这是注册 Activity 的代码

package com.fyp4201.universityguide;

import android.os.Bundle;

import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.View;
import android.widget.EditText;
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.JsonObjectRequest;
import com.android.volley.toolbox.StringRequest;
import com.android.volley.toolbox.Volley;
import android.widget.Toast;
import java.util.HashMap;
import java.util.Map;

public class Register extends AppCompatActivity {
private static final String REGISTER_URL = "http://jrfyp4201.site88.net/volleyRegister.php";
public static final String KEY_USERNAME = "username";
public static final String KEY_NAME = "name";
public static final String KEY_PASSWORD = "password";
public static final String KEY_EMAIL = "email";
public static final String KEY_CONTACTNO = "contactno";

private EditText etname,etuname,etpass,etconpass,etemail,etcontactno;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_register);
    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);

     etname= (EditText) findViewById(R.id.name);
     etuname= (EditText) findViewById(R.id.uname);
     etpass= (EditText) findViewById(R.id.pass);
     etconpass= (EditText) findViewById(R.id.conpass);
     etemail= (EditText) findViewById(R.id.email);
    etcontactno= (EditText) findViewById(R.id.contactno);
}

public void onRegisterbtnClick(View view ){
   registerUser();
}


public void registerUser(){
    final String username = etuname.getText().toString().trim();
    final String password = etpass.getText().toString().trim();
    final String name = etname.getText().toString().trim();
    final String email = etemail.getText().toString().trim();
    final String contactno = etcontactno.toString().trim();

    StringRequest stringRequest = new StringRequest(Request.Method.POST, REGISTER_URL,
            new Response.Listener<String>() {
                @Override
                public void onResponse(String response) {
                    Toast.makeText(Register.this,response,Toast.LENGTH_LONG).show();
                }
            },
            new Response.ErrorListener() {
                @Override
                public void onErrorResponse(VolleyError error) {
                    Toast.makeText(Register.this,error.toString(),Toast.LENGTH_LONG).show();
                }
            }){
        @Override
        protected Map<String,String> getParams(){
            Map<String,String> params = new HashMap<String, String>();
            params.put(KEY_USERNAME,username);
            params.put(KEY_PASSWORD,password);
            params.put(KEY_NAME, name);
            params.put(KEY_EMAIL, email);
            params.put(KEY_CONTACTNO, contactno);

            return params;
        }

    };

    RequestQueue requestQueue = Volley.newRequestQueue(this);
    requestQueue.add(stringRequest);
}
}

这是logcat错误文件

   Process: com.fyp4201.universityguide, PID: 20646
                                                                         java.lang.RuntimeException: Unable to start activity ComponentInfo{com.fyp4201.universityguide/com.fyp4201.universityguide.Register}: java.lang.NullPointerException
                                                                             at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2264)
                                                                             at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2313)
                                                                             at android.app.ActivityThread.access$1100(ActivityThread.java:141)
                                                                             at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1238)
                                                                             at android.os.Handler.dispatchMessage(Handler.java:102)
                                                                             at android.os.Looper.loop(Looper.java:136)
                                                                             at android.app.ActivityThread.main(ActivityThread.java:5333)
                                                                             at java.lang.reflect.Method.invokeNative(Native Method)
                                                                             at java.lang.reflect.Method.invoke(Method.java:515)
                                                                             at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:895)
                                                                             at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:711)
                                                                             at dalvik.system.NativeStart.main(Native Method)
                                                                          Caused by: java.lang.NullPointerException
                                                                             at com.fyp4201.universityguide.Register.onCreate(Register.java:20)
                                                                             at android.app.Activity.performCreate(Activity.java:5340)
                                                                             at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
                                                                             at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2228)
                                                                             at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2313) 
                                                                             at android.app.ActivityThread.access$1100(ActivityThread.java:141) 
                                                                             at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1238) 
                                                                             at android.os.Handler.dispatchMessage(Handler.java:102) 
                                                                             at android.os.Looper.loop(Looper.java:136) 
                                                                             at android.app.ActivityThread.main(ActivityThread.java:5333) 
                                                                             at java.lang.reflect.Method.invokeNative(Native Method) 
                                                                             at java.lang.reflect.Method.invoke(Method.java:515) 
                                                                             at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:895) 
                                                                             at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:711) 
                                                                             at dalvik.system.NativeStart.main(Native Method) 

注册 Activity 的XML文件

<?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"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
app:layout_behavior="@string/appbar_scrolling_view_behavior"
tools:context="com.fyp4201.universityguide.Register"
tools:showIn="@layout/activity_register">

<LinearLayout
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:layout_alignParentTop="true"
    android:layout_alignParentStart="true">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Name :"
        android:id="@+id/textView2" />

    <EditText
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:inputType="textPersonName"
        android:ems="10"
        android:id="@+id/editname"
         />

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Username :"
        android:id="@+id/textView3" />

    <EditText
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:id="@+id/edituname"
        />

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Password :"
        android:id="@+id/textView4" />

    <EditText
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:inputType="textPassword"
        android:ems="10"
        android:id="@+id/editpass"
        />

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Confirm Password :"
        android:id="@+id/textView7" />

    <EditText
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:inputType="textPassword"
        android:ems="10"
        android:id="@+id/editconpass"
       />

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="E-mail address :"
        android:id="@+id/textView5" />

    <EditText
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:inputType="textEmailAddress"
        android:ems="10"
        android:id="@+id/editemail"
       />

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Contact Number :"
        android:id="@+id/textView6" />

    <EditText
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:inputType="phone"
        android:ems="10"
        android:id="@+id/editcontactno"
       />

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Register"
        android:id="@+id/registerbtn"
        android:layout_gravity="center_horizontal"
        android:onClick="onRegisterbtnClick" />
</LinearLayout>

登录 Activity 的XML文件

<?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"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
app:layout_behavior="@string/appbar_scrolling_view_behavior"
tools:context="com.fyp4201.universityguide.LoginActivity"
tools:showIn="@layout/activity_login2">

<LinearLayout
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:layout_alignParentTop="true"
    android:layout_alignParentStart="true">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Username"
        android:id="@+id/textView1" />

    <EditText
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:id="@+id/loginuname" />

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Password"
        android:id="@+id/textView" />

    <EditText
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:inputType="textPassword"
        android:ems="10"
        android:id="@+id/loginpass" />

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Login"
        android:id="@+id/login"
        android:layout_gravity="center_horizontal"
        android:clickable="true"
        android:focusableInTouchMode="false"
        android:onClick="onLoginClick" />

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textAppearance="?android:attr/textAppearanceMedium"
        android:text="Register Here!"
        android:id="@+id/register"
        android:layout_gravity="center_horizontal"
        android:textColor="@color/accent_material_light"
        android:clickable="true"
        android:onClick="onRegisterClick" />

</LinearLayout>

请告诉我我错过了什么。谢谢。

Answer 1

检查xml文件中的所有ID，并在Java中更正其名称。
似乎您引用的是与此 Activity 无关的另一个xml文件的id，就像您可能在注册 Activity 中引用了登录xml文件的用户名字段一样，反之亦然