java按钮不起作用
我在第二个活动和第三个活动中添加了一个按钮,但单击时会出现错误。 这里是第一个活动Java文件
package com.example.ephraimcohen.prestwichlanguageschool;
import 安卓.content.Intent;
import 安卓.provider.AlarmClock;
import 安卓.support.v7.app.AppCompatActivity;
import 安卓.os.Bundle;
import 安卓.view.View;
import 安卓.widget.EditText;
import static 安卓.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);
}
}
这是第二个Java文件
package com.example.ephraimcohen.prestwichlanguageschool;
import 安卓.app.Activity;
import 安卓.content.Intent;
import 安卓.support.v7.app.AppCompatActivity;
import 安卓.os.Bundle;
import 安卓.view.View;
import 安卓.widget.Button;
import 安卓.widget.EditText;
import 安卓.widget.TextView;
import static 安卓.provider.AlarmClock.EXTRA_MESSAGE;
import static 安卓.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);
}
}
这是第三个Java文件
package com.example.ephraimcohen.prestwichlanguageschool;
import 安卓.app.Notification;
import 安卓.content.Intent;
import 安卓.support.v7.app.AppCompatActivity;
import 安卓.os.Bundle;
import 安卓.view.View;
import 安卓.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);
}
}
我已经设法通过按钮将第一页连接到第二页,但第二页不允许我转到第三页。我已经把所有的代码放进去了,但当按下第二页的按钮时,它只是重新启动应用程序。重新启动后,它将关闭应用程序。 任何建议都将不胜感激
第二个XML文件
<?xml version="1.0" encoding="utf-8"?>
<安卓.support.constraint.ConstraintLayout
xmlns:安卓="http://schemas.安卓.com/apk/res/安卓"
xmlns:app="http://schemas.安卓.com/apk/res-auto"
xmlns:tools="http://schemas.安卓.com/tools"
安卓:layout_width="match_parent"
安卓:layout_height="match_parent"
tools:context="com.example.ephraimcohen.prestwichlanguageschool.languageselection">
<ImageView
安卓:id="@+id/imageView2"
安卓:layout_width="0dp"
安卓:layout_height="77dp"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toEndOf="@+id/imageView3"
app:layout_constraintTop_toTopOf="parent"
app:srcCompat="@drawable/logo"
安卓:contentDescription="@string/todo" />
<ImageView
安卓:id="@+id/imageView3"
安卓:layout_width="wrap_content"
安卓:layout_height="wrap_content"
安卓:layout_marginEnd="265dp"
安卓:layout_marginStart="81dp"
安卓:layout_marginTop="2dp"
app:layout_constraintEnd_toStartOf="@+id/imageView2"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@+id/textView"
app:srcCompat="@drawable/italianflag" 安卓:contentDescription="@string/todo"
安卓:layout_marginRight="265dp"
安卓:layout_marginLeft="81dp" />
<ImageView
安卓:id="@+id/imageView4"
安卓:layout_width="wrap_content"
安卓: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" 安卓:contentDescription="@string/todo" />
<Button
安卓:id="@+id/button3"
安卓:layout_width="wrap_content"
安卓:layout_height="wrap_content"
安卓:layout_marginStart="34dp"
安卓:layout_marginTop="25dp"
安卓:text="@string/italian"
安卓:onClick="sendMessage"
app:layout_constraintStart_toEndOf="@+id/imageView3"
app:layout_constraintTop_toBottomOf="@+id/textView"
安卓:layout_marginLeft="34dp" />
<Button
安卓:id="@+id/button4"
安卓:layout_width="wrap_content"
安卓:layout_height="wrap_content"
安卓:layout_marginBottom="22dp"
安卓:layout_marginStart="34dp"
安卓:text="@string/polish"
app:layout_constraintBottom_toBottomOf="@+id/imageView4"
app:layout_constraintStart_toEndOf="@+id/imageView4"
安卓:layout_marginLeft="34dp" />
<TextView
安卓:id="@+id/textView"
安卓:layout_width="wrap_content"
安卓:layout_height="wrap_content"
安卓:layout_marginEnd="11dp"
安卓:layout_marginStart="106dp"
安卓:text="@string/choose_a_language"
安卓:textAppearance="@style/TextAppearance.AppCompat.Display2"
app:layout_constraintEnd_toStartOf="@+id/imageView2"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
安卓:layout_marginRight="11dp"
安卓:layout_marginLeft="106dp" />
</安卓.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 安卓:onClick
at 安卓.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:293)
at 安卓.view.View.performClick(View.java:5640)
at 安卓.view.View$PerformClick.run(View.java:22455)
at 安卓.os.Handler.handleCallback(Handler.java:751)
at 安卓.os.Handler.dispatchMessage(Handler.java:95)
at 安卓.os.Looper.loop(Looper.java:154)
at 安卓.app.ActivityThread.main(ActivityThread.java:6165)
at java.lang.reflect.Method.invoke(Native Method)
at com.安卓.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:888)
at com.安卓.internal.os.ZygoteInit.main(ZygoteInit.java:778)
Caused by: java.lang.reflect.InvocationTargetException
at java.lang.reflect.Method.invoke(Native Method)
at 安卓.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:288)
at 安卓.view.View.performClick(View.java:5640)
at 安卓.view.View$PerformClick.run(View.java:22455)
at 安卓.os.Handler.handleCallback(Handler.java:751)
at 安卓.os.Handler.dispatchMessage(Handler.java:95)
at 安卓.os.Looper.loop(Looper.java:154)
at 安卓.app.ActivityThread.main(ActivityThread.java:6165)
at java.lang.reflect.Method.invoke(Native Method)
at com.安卓.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:888)
at com.安卓.internal.os.ZygoteInit.main(ZygoteInit.java:778)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method '安卓.text.Editable 安卓.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 安卓.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:288)
at 安卓.view.View.performClick(View.java:5640)
at 安卓.view.View$PerformClick.run(View.java:22455)
at 安卓.os.Handler.handleCallback(Handler.java:751)
at 安卓.os.Handler.dispatchMessage(Handler.java:95)
at 安卓.os.Looper.loop(Looper.java:154)
at 安卓.app.ActivityThread.main(ActivityThread.java:6165)
at java.lang.reflect.Method.invoke(Native Method)
at com.安卓.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:888)
at com.安卓.internal.os.ZygoteInit.main(ZygoteInit.java:778)
Application terminated.
# 1 楼答案
在
languageselection
类中:您正在调用相同的活动,而不是第三个活动(如上所述)
# 2 楼答案
第三个活动的java类是
catagoryitalian
,但在第二个活动的java类中的sendMessage
方法中,您在Intent
中传递了错误的类名换成