Android Studio两个按钮Java代码错误_Java_Android

Android Studio两个按钮Java代码错误

java android

Android Studio两个按钮Java代码错误,java,android,Java,Android,下面是概要文件活动的java代码。我只做了大约30天，很多事情仍然让我困惑当我运行模拟器时，它会打开，然后在第一个按钮后崩溃它应该将用户发送到第二个活动运行Logcat时，它挂在下面页面的第26行，表示它讨厌我的监听器中的按钮2。帮助 Logcat文件如下： import android.content.Intent; import android.support.v7.app.AppCompatActivity; import android.os.Bundle; import and

下面是概要文件活动的java代码。我只做了大约30天，很多事情仍然让我困惑

当我运行模拟器时，它会打开，然后在第一个按钮后崩溃它应该将用户发送到第二个活动

运行Logcat时，它挂在下面页面的第26行，表示它讨厌我的监听器中的按钮2。帮助

Logcat文件如下：

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

public class ProfileActivity extends AppCompatActivity {

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

        // Button Click Goes to Main Activity
        Button button1 = (Button) findViewById(R.id.start_over);
        button1.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                back();
            }
        });
        // Button Click Goes To Third Activity
        Button button2 = (Button) findViewById(R.id.forward);
        button2.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                forward();
            }
        });
    }

    private void back() {
        Intent intent = new Intent(this, MainActivity.class);
        startActivity(intent);

    }

    private void forward() {
        Intent intent = new Intent(this, ThirdActivity.class);
        startActivity(intent);

    }
}

MainActivity.XML如下：

FATAL EXCEPTION: main
                                                                Process: com.defy, PID: 2481
                                                                java.lang.RuntimeException: Unable to start activity ComponentInfo{com.defy/com.defy.ProfileActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
                                                                    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2665)
                                                                    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2726)
                                                                    at android.app.ActivityThread.-wrap12(ActivityThread.java)
                                                                    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1477)
                                                                    at android.os.Handler.dispatchMessage(Handler.java:102)
                                                                    at android.os.Looper.loop(Looper.java:154)
                                                                    at android.app.ActivityThread.main(ActivityThread.java:6119)
                                                                    at java.lang.reflect.Method.invoke(Native Method)
                                                                    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
                                                                    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)
                                                                 Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
                                                                    at com.defy.ProfileActivity.onCreate(ProfileActivity.java:26)
                                                                    at android.app.Activity.performCreate(Activity.java:6679)
                                                                    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1118)
                                                                    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2618)
                                                                    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2726) 
                                                                    at android.app.ActivityThread.-wrap12(ActivityThread.java) 
                                                                    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1477) 
                                                                    at android.os.Handler.dispatchMessage(Handler.java:102) 
                                                                    at android.os.Looper.loop(Looper.java:154) 
                                                                    at android.app.ActivityThread.main(ActivityThread.java:6119) 
                                                                    at java.lang.reflect.Method.invoke(Native Method)

<application
    android:allowBackup="true"
    android:icon="@mipmap/ic_launcher"
    android:label="@string/app_name"
    android:roundIcon="@mipmap/ic_launcher_round"
    android:supportsRtl="true"
    android:theme="@style/AppTheme">
    <activity android:name=".MainActivity">
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />

            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>
    <activity android:name=".ProfileActivity" />
    <activity android:name=".ThirdActivity"></activity>
</application>

最后是下面的清单文件：

    package com.defy.trailmaster;

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

public class MainActivity extends AppCompatActivity {

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

        //Button Click Goes To Profile Activity
        Button button = (Button) findViewById(R.id.start_hiking);
        button.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View view) {
                hike();
            }
        });
    }

    private void hike() {

        Intent intent = new Intent(this, ProfileActivity.class);
        startActivity(intent);
    }
}

配置文件活动XML如下：

FATAL EXCEPTION: main
                                                                Process: com.defy, PID: 2481
                                                                java.lang.RuntimeException: Unable to start activity ComponentInfo{com.defy/com.defy.ProfileActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
                                                                    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2665)
                                                                    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2726)
                                                                    at android.app.ActivityThread.-wrap12(ActivityThread.java)
                                                                    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1477)
                                                                    at android.os.Handler.dispatchMessage(Handler.java:102)
                                                                    at android.os.Looper.loop(Looper.java:154)
                                                                    at android.app.ActivityThread.main(ActivityThread.java:6119)
                                                                    at java.lang.reflect.Method.invoke(Native Method)
                                                                    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
                                                                    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)
                                                                 Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
                                                                    at com.defy.ProfileActivity.onCreate(ProfileActivity.java:26)
                                                                    at android.app.Activity.performCreate(Activity.java:6679)
                                                                    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1118)
                                                                    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2618)
                                                                    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2726) 
                                                                    at android.app.ActivityThread.-wrap12(ActivityThread.java) 
                                                                    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1477) 
                                                                    at android.os.Handler.dispatchMessage(Handler.java:102) 
                                                                    at android.os.Looper.loop(Looper.java:154) 
                                                                    at android.app.ActivityThread.main(ActivityThread.java:6119) 
                                                                    at java.lang.reflect.Method.invoke(Native Method)

<application
    android:allowBackup="true"
    android:icon="@mipmap/ic_launcher"
    android:label="@string/app_name"
    android:roundIcon="@mipmap/ic_launcher_round"
    android:supportsRtl="true"
    android:theme="@style/AppTheme">
    <activity android:name=".MainActivity">
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />

            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>
    <activity android:name=".ProfileActivity" />
    <activity android:name=".ThirdActivity"></activity>
</application>

它很可能由于R.id.forward而崩溃，按钮2为空。看起来您要么将按钮id命名为其他名称，要么错过了它

发布ProfileActivity的XML，这是您的问题。按钮2现在应该指徒步旅行

    <?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:id="@+id/activity_profile"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="com.defy.trailmaster.ProfileActivity">

    <ImageView
        android:id="@+id/background"
        android:layout_width="0dp"
        android:layout_height="0dp"
        android:contentDescription="@string/app_name"
        android:scaleType="centerCrop"
        android:src="@drawable/background"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintHorizontal_bias="0.0"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="1.0" />

    <Button
        android:id="@+id/start_over"
        android:layout_width="95dp"
        android:layout_height="35dp"
        android:background="#000000"
        android:text="@string/app_back"
        android:textColor="#FDFEFE"
        android:textStyle="bold"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintHorizontal_bias="0.145"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.966" />

    <Button
        android:id="@+id/hike_now"
        android:layout_width="95dp"
        android:layout_height="35dp"
        android:background="#000000"
        android:text="@string/app_hike"
        android:textColor="#FDFEFE"
        android:textStyle="bold"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintHorizontal_bias="0.868"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.966" />

    <ImageView
        android:id="@+id/tent"
        android:layout_width="121dp"
        android:layout_height="96dp"
        android:contentDescription="@string/app_name"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintHorizontal_bias="0.06"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.26"
        app:srcCompat="@drawable/tent" />

    <ImageView
        android:id="@+id/left_hiker"
        android:layout_width="92dp"
        android:layout_height="90dp"
        android:layout_marginBottom="0dp"
        android:layout_marginStart="42dp"
        android:layout_marginLeft="42dp"
        android:layout_marginRight="8dp"
        android:layout_marginEnd="8dp"
        android:contentDescription="@string/app_name"
        app:layout_constraintBottom_toTopOf="@+id/start_over"
        app:layout_constraintHorizontal_bias="0.0"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toLeftOf="@+id/hiker_right"
        app:srcCompat="@drawable/hiker_left" />

    <ImageView
        android:id="@+id/hiker_right"
        android:layout_width="92dp"
        android:layout_height="90dp"
        android:layout_marginBottom="8dp"
        android:layout_marginLeft="8dp"
        android:layout_marginRight="37dp"
        android:layout_marginTop="8dp"
        android:contentDescription="@string/app_name"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintHorizontal_bias="0.991"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.889"
        app:srcCompat="@drawable/hiker_right"
        tools:ignore="MissingConstraints,RtlHardcoded" />

</android.support.constraint.ConstraintLayout>

请将活动的布局xml添加到问题中。请同时发布xml。发布manifistpost日志输出。26号线在哪？Logcat是added@Stack_Master没问题！我最近开始为android开发，一开始也让我很沮丧。

    <?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:id="@+id/activity_profile"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="com.defy.trailmaster.ProfileActivity">

    <ImageView
        android:id="@+id/background"
        android:layout_width="0dp"
        android:layout_height="0dp"
        android:contentDescription="@string/app_name"
        android:scaleType="centerCrop"
        android:src="@drawable/background"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintHorizontal_bias="0.0"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="1.0" />

    <Button
        android:id="@+id/start_over"
        android:layout_width="95dp"
        android:layout_height="35dp"
        android:background="#000000"
        android:text="@string/app_back"
        android:textColor="#FDFEFE"
        android:textStyle="bold"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintHorizontal_bias="0.145"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.966" />

    <Button
        android:id="@+id/hike_now"
        android:layout_width="95dp"
        android:layout_height="35dp"
        android:background="#000000"
        android:text="@string/app_hike"
        android:textColor="#FDFEFE"
        android:textStyle="bold"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintHorizontal_bias="0.868"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.966" />

    <ImageView
        android:id="@+id/tent"
        android:layout_width="121dp"
        android:layout_height="96dp"
        android:contentDescription="@string/app_name"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintHorizontal_bias="0.06"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.26"
        app:srcCompat="@drawable/tent" />

    <ImageView
        android:id="@+id/left_hiker"
        android:layout_width="92dp"
        android:layout_height="90dp"
        android:layout_marginBottom="0dp"
        android:layout_marginStart="42dp"
        android:layout_marginLeft="42dp"
        android:layout_marginRight="8dp"
        android:layout_marginEnd="8dp"
        android:contentDescription="@string/app_name"
        app:layout_constraintBottom_toTopOf="@+id/start_over"
        app:layout_constraintHorizontal_bias="0.0"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toLeftOf="@+id/hiker_right"
        app:srcCompat="@drawable/hiker_left" />

    <ImageView
        android:id="@+id/hiker_right"
        android:layout_width="92dp"
        android:layout_height="90dp"
        android:layout_marginBottom="8dp"
        android:layout_marginLeft="8dp"
        android:layout_marginRight="37dp"
        android:layout_marginTop="8dp"
        android:contentDescription="@string/app_name"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintHorizontal_bias="0.991"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.889"
        app:srcCompat="@drawable/hiker_right"
        tools:ignore="MissingConstraints,RtlHardcoded" />

</android.support.constraint.ConstraintLayout>

 Final Button button2 = (Button) findViewById(R.id.hike_now);