按钮不会工作

我已经添加了一个按钮，从我的第二个活动和第三，但它会提供一个错误，当它被点击。这是第一个活动的Java文件。按钮不会工作

package com.example.ephraimcohen.prestwichlanguageschool; 

import android.content.Intent; 
import android.provider.AlarmClock; 
import android.support.v7.app.AppCompatActivity; 
import android.os.Bundle; 
import android.view.View; 
import android.widget.EditText; 

import static android.provider.AlarmClock.EXTRA_MESSAGE; 

public class MainActivity extends AppCompatActivity { 
    public static final String EXTRA_MESSAGE = AlarmClock.EXTRA_MESSAGE ; 

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

    /** Called when the user taps the Send button */ 
    public void sendMessage(View view) { 
     Intent intent = new Intent(this, languageselection.class); 
     EditText editText = (EditText) findViewById(R.id.editText); 
     String message = editText.getText().toString(); 
     intent.putExtra(EXTRA_MESSAGE, message); 
     startActivity(intent); 
    } 
}

这里是第二的Java文件

package com.example.ephraimcohen.prestwichlanguageschool; 

import android.app.Activity; 
import android.content.Intent; 
import android.support.v7.app.AppCompatActivity; 
import android.os.Bundle; 
import android.view.View; 
import android.widget.Button; 
import android.widget.EditText; 
import android.widget.TextView; 

import static android.provider.AlarmClock.EXTRA_MESSAGE; 
import static android.support.v4.app.NotificationCompat.EXTRA_MESSAGES; 

public class languageselection extends AppCompatActivity { 


    public static final String EXTRA_MESSAGE ="extra_message"; 

    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 

     setContentView(R.layout.activity_languageselection); 

     // Get the Intent that started this activity and extract the string 
     Intent intent = getIntent(); 
     String message = intent.getStringExtra(MainActivity.EXTRA_MESSAGE); 

     // Capture the layout's TextView and set the string as its text 
     TextView textView = findViewById(R.id.textView); 
     textView.setText(message); 
    } 

    /** Called when the user taps the Send button */ 
    public void sendMessage(View view) { 
     Intent intent = new Intent(this, languageselection.class); 
     EditText editText = (EditText) findViewById(R.id.editText); 
     String message = editText.getText().toString(); 
     intent.putExtra(EXTRA_MESSAGE, message); 
     startActivity(intent); 
    } 
}

这里是第三的Java文件。

package com.example.ephraimcohen.prestwichlanguageschool; 

     import android.app.Notification; 
     import android.content.Intent; 
     import android.support.v7.app.AppCompatActivity; 
     import android.os.Bundle; 
     import android.view.View; 
     import android.widget.TextView; 

     import java.util.Locale; 

public class catagoryitalian extends AppCompatActivity { 

    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 

     setContentView(R.layout.activity_catagoryitalian); 

     // Get the Intent that started this activity and extract the string 
     Intent intent = getIntent(); 
     String message = intent.getStringExtra(languageselection.EXTRA_MESSAGE); 

     // Capture the layout's TextView and set the string as its text 
     TextView textView = findViewById(R.id.textView); 
     textView.setText(message); 
    } 
}

我设法得到的第一页通过一个按钮连接到第二，但第二页不会让我去第三页。我已经把所有的代码，但它只是重新启动应用程序，当第二页上的按钮被按下。重新启动后，它会关闭应用程序。任何意见将非常感激。

二XML文件

<?xml version="1.0" encoding="utf-8"?> 
<android.support.constraint.ConstraintLayout 
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" 


    tools:context="com.example.ephraimcohen.prestwichlanguageschool.languageselection"> 

    <ImageView 
     android:id="@+id/imageView2" 
     android:layout_width="0dp" 
     android:layout_height="77dp" 
     app:layout_constraintEnd_toEndOf="parent" 
     app:layout_constraintStart_toEndOf="@+id/imageView3" 
     app:layout_constraintTop_toTopOf="parent" 
     app:srcCompat="@drawable/logo" 
android:contentDescription="@string/todo" /> 

    <ImageView 
     android:id="@+id/imageView3" 
     android:layout_width="wrap_content" 
     android:layout_height="wrap_content" 
     android:layout_marginEnd="265dp" 
     android:layout_marginStart="81dp" 
     android:layout_marginTop="2dp" 
     app:layout_constraintEnd_toStartOf="@+id/imageView2" 
     app:layout_constraintStart_toStartOf="parent" 
     app:layout_constraintTop_toBottomOf="@+id/textView" 
     app:srcCompat="@drawable/italianflag" android:contentDescription="@string/todo" 
     android:layout_marginRight="265dp" 
     android:layout_marginLeft="81dp" /> 

    <ImageView 
     android:id="@+id/imageView4" 
     android:layout_width="wrap_content" 
     android:layout_height="wrap_content" 
     app:layout_constraintBottom_toBottomOf="parent" 
     app:layout_constraintStart_toStartOf="@+id/imageView3" 
     app:layout_constraintTop_toTopOf="parent" 
     app:layout_constraintVertical_bias="0.857" 
     app:srcCompat="@drawable/polishflag" android:contentDescription="@string/todo" /> 

    <Button 
     android:id="@+id/button3" 
     android:layout_width="wrap_content" 
     android:layout_height="wrap_content" 
     android:layout_marginStart="34dp" 
     android:layout_marginTop="25dp" 
     android:text="@string/italian" 
     android:onClick="sendMessage" 
     app:layout_constraintStart_toEndOf="@+id/imageView3" 
     app:layout_constraintTop_toBottomOf="@+id/textView" 
     android:layout_marginLeft="34dp" /> 

    <Button 
     android:id="@+id/button4" 
     android:layout_width="wrap_content" 
     android:layout_height="wrap_content" 
     android:layout_marginBottom="22dp" 
     android:layout_marginStart="34dp" 
     android:text="@string/polish" 
     app:layout_constraintBottom_toBottomOf="@+id/imageView4" 
     app:layout_constraintStart_toEndOf="@+id/imageView4" 
     android:layout_marginLeft="34dp" /> 

    <TextView 
     android:id="@+id/textView" 
     android:layout_width="wrap_content" 
     android:layout_height="wrap_content" 
     android:layout_marginEnd="11dp" 
     android:layout_marginStart="106dp" 
     android:text="@string/choose_a_language" 
     android:textAppearance="@style/TextAppearance.AppCompat.Display2" 
     app:layout_constraintEnd_toStartOf="@+id/imageView2" 
     app:layout_constraintStart_toStartOf="parent" 
     app:layout_constraintTop_toTopOf="parent" 
     android:layout_marginRight="11dp" 
     android:layout_marginLeft="106dp" /> 
</android.support.constraint.ConstraintLayout>

堆栈跟踪

E/AndroidRuntime: FATAL EXCEPTION: main 
        Process: com.example.ephraimcohen.prestwichlanguageschool, PID: 30038 
        java.lang.IllegalStateException: Could not execute method for android:onClick 
         at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:293) 
         at android.view.View.performClick(View.java:5640) 
         at android.view.View$PerformClick.run(View.java:22455) 
         at android.os.Handler.handleCallback(Handler.java:751) 
         at android.os.Handler.dispatchMessage(Handler.java:95) 
         at android.os.Looper.loop(Looper.java:154) 
         at android.app.ActivityThread.main(ActivityThread.java:6165) 
         at java.lang.reflect.Method.invoke(Native Method) 
         at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:888) 
         at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:778) 
        Caused by: java.lang.reflect.InvocationTargetException 
         at java.lang.reflect.Method.invoke(Native Method) 
         at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:288) 
         at android.view.View.performClick(View.java:5640)  
         at android.view.View$PerformClick.run(View.java:22455)  
         at android.os.Handler.handleCallback(Handler.java:751)  
         at android.os.Handler.dispatchMessage(Handler.java:95)  
         at android.os.Looper.loop(Looper.java:154)  
         at android.app.ActivityThread.main(ActivityThread.java:6165)  
         at java.lang.reflect.Method.invoke(Native Method)  
         at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:888)  
         at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:778)  
        Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.text.Editable android.widget.EditText.getText()' on a null object reference 
         at com.example.ephraimcohen.prestwichlanguageschool.languageselection.sendMessage(languageselection.java:39) 
         at java.lang.reflect.Method.invoke(Native Method)  
         at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:288)  
         at android.view.View.performClick(View.java:5640)  
         at android.view.View$PerformClick.run(View.java:22455)  
         at android.os.Handler.handleCallback(Handler.java:751)  
         at android.os.Handler.dispatchMessage(Handler.java:95)  
         at android.os.Looper.loop(Looper.java:154)  
         at android.app.ActivityThread.main(ActivityThread.java:6165)  
         at java.lang.reflect.Method.invoke(Native Method)  
         at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:888)  
         at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:778)  
Application terminated.

来源

2017-12-27 Ephraim Cohen

写错误堆栈跟踪 – VolkanSahin45

请添加第2次活动的布局XML和异常记录。 – Christopher

从第二类languageselection调用第三类。 Intent intent = new Intent（this，catagoryitalian.class）; 顺便请发布您收到的错误。 – lib4

在类languageselection：

public void sendMessage(View view) { 
    Intent intent = new Intent(this, catagoryitalian.class); 
    ... 
}

要调用同一个活动，而不是第三个活动（如上）。

来源

2017-12-27 18:35:42

你的第三个活动的java类是catagoryitalian但在第二个活动的java类里面sendMessage方法，你在Intent

Intent intent = new Intent(this, languageselection.class);

更改它传递了错误的类名

Intent intent = new Intent(this, catagoryitalian.class);

来源

2017-12-27 18:36:41 Yousaf

我改变了这一点，应用程序仍然无法工作 –

这将是另一个问题。为了获得帮助，你需要发布堆栈跟踪。 – Yousaf

你是怎么做到的 –

按钮不会工作

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