Java Android Studio应用程序在添加蓝牙连接代码后崩溃

我目前正在使用一个应用程序，通过蓝牙控制arduino。我为菜单等添加了一些活动。昨天，我添加了一个新的活动，用于将我的设备连接到蓝牙模块

甚至可以在一个活动中连接到设备，并在另一个活动中实际控制（发送信件）它吗

也就是说，每次我试图打开带有蓝牙代码的活动时，应用程序都会崩溃。其他每一项活动都可以顺利进行

我希望有人能帮忙

这是我的密码：

MainActivity.java（控制模块的活动）：

BT_Classic.java（连接到模块的活动）：

Crashlog：

2018-09-12 17:25:36.957 10178-10178/com.car.bluetooth.bluetoothcar 
E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.car.bluetooth.bluetoothcar, PID: 10178
java.lang.RuntimeException: Unable to start activity  


ComponentInfo{com.car.bluetooth.bluetoothcar/com.car.bluetooth.bluetoothcar.BT_Classic}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
        at 
    android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2830)
        at 
    android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2909)
        at android.app.ActivityThread.-wrap11(Unknown Source:0)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1606)
        at android.os.Handler.dispatchMessage(Handler.java:105)
        at android.os.Looper.loop(Looper.java:164)
        at android.app.ActivityThread.main(ActivityThread.java:6592)
        at java.lang.reflect.Method.invoke(Native Method)
        at 
    com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:769)
     Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
        at com.car.bluetooth.bluetoothcar.BT_Classic.onCreate(BT_Classic.java:78)
        at android.app.Activity.performCreate(Activity.java:6984)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1235)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2783)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2909) 
        at android.app.ActivityThread.-wrap11(Unknown Source:0) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1606) 
        at android.os.Handler.dispatchMessage(Handler.java:105) 
        at android.os.Looper.loop(Looper.java:164) 
        at android.app.ActivityThread.main(ActivityThread.java:6592) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:769) 

---

btonButton

和

btoffButton

未初始化且等于null

您应该使用

findViewById（）

初始化它们，就像使用pairedButton一样

btonButton = (Button) findViewById(R.id.put_here_btn_on_id);
btoffButton = (Button) findViewById(R.id.put_here_btn_off_id);

---

btonButton和btoffButton尚未初始化，然后您正在调用

setonClickListener

这会导致

NPE

内部

onCreate

如下初始化：

btonButton = (Button) findViewById(R.id.btonButton);
btoffButton = (Button) findViewById(R.id.btoffButton);

---

在崩溃时向我们显示错误的日志。。。此外，与您的问题无关，类的名称需要以大写字母开头。我告诉你这些是因为connectActivity和SettingsActivity我更新了帖子：）谢谢，这才是问题所在。我现在觉得自己很笨。

apply plugin: 'com.android.application'

android {
compileSdkVersion 28
defaultConfig {
    applicationId "com.car.bluetooth.bluetoothcar"
    minSdkVersion '16'
    targetSdkVersion 28
    versionCode 1
    versionName "1.0"
    testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
}
buildTypes {
    release {
        minifyEnabled false
        proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
    }
}
}

dependencies {
implementation fileTree(dir: 'libs', include: ['*.jar'])
implementation 'androidx.appcompat:appcompat:1.0.0-beta01'
implementation 'android.arch.navigation:navigation-fragment:1.0.0-alpha05'
implementation 'android.arch.navigation:navigation-ui:1.0.0-alpha05'
implementation 'androidx.constraintlayout:constraintlayout:1.1.2'
implementation 'com.google.android.material:material:1.0.0-beta01'
testImplementation 'junit:junit:4.12'
androidTestImplementation 'androidx.test:runner:1.1.0-alpha4'
androidTestImplementation 'androidx.test.espresso:espresso-core:3.1.0-alpha4'
}

2018-09-12 17:25:36.957 10178-10178/com.car.bluetooth.bluetoothcar 
E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.car.bluetooth.bluetoothcar, PID: 10178
java.lang.RuntimeException: Unable to start activity  


ComponentInfo{com.car.bluetooth.bluetoothcar/com.car.bluetooth.bluetoothcar.BT_Classic}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
        at 
    android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2830)
        at 
    android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2909)
        at android.app.ActivityThread.-wrap11(Unknown Source:0)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1606)
        at android.os.Handler.dispatchMessage(Handler.java:105)
        at android.os.Looper.loop(Looper.java:164)
        at android.app.ActivityThread.main(ActivityThread.java:6592)
        at java.lang.reflect.Method.invoke(Native Method)
        at 
    com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:769)
     Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
        at com.car.bluetooth.bluetoothcar.BT_Classic.onCreate(BT_Classic.java:78)
        at android.app.Activity.performCreate(Activity.java:6984)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1235)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2783)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2909) 
        at android.app.ActivityThread.-wrap11(Unknown Source:0) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1606) 
        at android.os.Handler.dispatchMessage(Handler.java:105) 
        at android.os.Looper.loop(Looper.java:164) 
        at android.app.ActivityThread.main(ActivityThread.java:6592) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:769) 

btonButton = (Button) findViewById(R.id.put_here_btn_on_id);
btoffButton = (Button) findViewById(R.id.put_here_btn_off_id);

btonButton = (Button) findViewById(R.id.btonButton);
btoffButton = (Button) findViewById(R.id.btoffButton);