Question

我制作了一个启动加速计传感器的android项目，并将传感器x，y，z数据存储在一个文件中。我在方法start.setEnabled(false)中添加了代码行stop.setEnabled(true)和start，从那以后我的代码在start崩溃了。错误如下：



E/AndroidRuntime: FATAL EXCEPTION: main
                  Process: com.example.zhenga1.photojewel, PID: 27298
                  java.lang.IllegalStateException: Could not execute method for android:onClick
                      at android.view.View$DeclaredOnClickListener.onClick(View.java:4507)
                      at android.view.View.performClick(View.java:5267)
                      at android.view.View$PerformClick.run(View.java:21540)
                      at android.os.Handler.handleCallback(Handler.java:815)
                      at android.os.Handler.dispatchMessage(Handler.java:104)
                      at android.os.Looper.loop(Looper.java:207)
                      at android.app.ActivityThread.main(ActivityThread.java:5710)
                      at java.lang.reflect.Method.invoke(Native Method)
                      at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:900)
                      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:761)
                   Caused by: java.lang.reflect.InvocationTargetException
                      at java.lang.reflect.Method.invoke(Native Method)
                      at android.view.View$DeclaredOnClickListener.onClick(View.java:4502)
                      at android.view.View.performClick(View.java:5267) 
                      at android.view.View$PerformClick.run(View.java:21540) 
                      at android.os.Handler.handleCallback(Handler.java:815) 
                      at android.os.Handler.dispatchMessage(Handler.java:104) 
                      at android.os.Looper.loop(Looper.java:207) 
                      at android.app.ActivityThread.main(ActivityThread.java:5710) 
                      at java.lang.reflect.Method.invoke(Native Method) 
                      at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:900) 
                      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:761) 
                   Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setEnabled(boolean)' on a null object reference
                      at com.example.zhenga1.photojewel.Main3Activity.start(Main3Activity.java:120)
                      at java.lang.reflect.Method.invoke(Native Method) 
                      at android.view.View$DeclaredOnClickListener.onClick(View.java:4502) 
                      at android.view.View.performClick(View.java:5267) 
                      at android.view.View$PerformClick.run(View.java:21540) 
                      at android.os.Handler.handleCallback(Handler.java:815) 
                      at android.os.Handler.dispatchMessage(Handler.java:104) 
                      at android.os.Looper.loop(Looper.java:207) 
                      at android.app.ActivityThread.main(ActivityThread.java:5710) 
                      at java.lang.reflect.Method.invoke(Native Method)

E/AndroidRuntime: FATAL EXCEPTION: main Process: com.example.zhenga1.photojewel, PID: 27298 java.lang.IllegalStateException: Could not execute method for android:onClick at android.view.View$DeclaredOnClickListener.onClick(View.java:4507) at android.view.View.performClick(View.java:5267) at android.view.View$PerformClick.run(View.java:21540) at android.os.Handler.handleCallback(Handler.java:815) at android.os.Handler.dispatchMessage(Handler.java:104) at android.os.Looper.loop(Looper.java:207) at android.app.ActivityThread.main(ActivityThread.java:5710) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:900) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:761) Caused by: java.lang.reflect.InvocationTargetException at java.lang.reflect.Method.invoke(Native Method) at android.view.View$DeclaredOnClickListener.onClick(View.java:4502) at android.view.View.performClick(View.java:5267) at android.view.View$PerformClick.run(View.java:21540) at android.os.Handler.handleCallback(Handler.java:815) at android.os.Handler.dispatchMessage(Handler.java:104) at android.os.Looper.loop(Looper.java:207) at android.app.ActivityThread.main(ActivityThread.java:5710) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:900) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:761) Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setEnabled(boolean)' on a null object reference at com.example.zhenga1.photojewel.Main3Activity.start(Main3Activity.java:120) at java.lang.reflect.Method.invoke(Native Method) at android.view.View$DeclaredOnClickListener.onClick(View.java:4502) at android.view.View.performClick(View.java:5267) at android.view.View$PerformClick.run(View.java:21540) at android.os.Handler.handleCallback(Handler.java:815) at android.os.Handler.dispatchMessage(Handler.java:104) at android.os.Looper.loop(Looper.java:207) at android.app.ActivityThread.main(ActivityThread.java:5710) at java.lang.reflect.Method.invoke(Native Method) 更新：这是我的.xml主布局文件：

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="16dp"
    android:paddingLeft="16dp"
    android:paddingRight="16dp"
    android:paddingTop="16dp"
    tools:context="com.example.zhenga1.photojewel.MainActivity">

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Start Accelerometer"
        android:id="@+id/button"
        android:onClick="start"
        android:layout_marginTop="300dp"
        android:layout_marginStart="0dp"
        android:layout_marginLeft="0dp"
        android:textStyle="normal"
        android:textSize="6pt"/>
    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="End Accelerometer"
        android:onClick="end"
        android:id="@+id/button2"
        android:layout_alignParentRight="true"
        android:layout_marginTop="300dp"
        android:textStyle="normal"
        android:textSize="6pt"/>

    <ImageView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/imageView2"
        android:layout_marginTop="200dp"
        android:layout_marginLeft="150dp"
        android:src="@mipmap/vibrator_pic"/>

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textAppearance="?android:attr/textAppearanceMedium"
        android:text="Medium Text"
        android:id="@+id/textView"
        android:layout_alignParentBottom="true"
        android:layout_marginTop="600dp"
        android:layout_marginLeft="0dp"
        android:layout_marginStart="0dp"/>

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textAppearance="?android:attr/textAppearanceMedium"
        android:text="Medium Text"
        android:id="@+id/textView2"
        android:layout_alignParentBottom="true"
        android:layout_centerHorizontal="true"/>

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textAppearance="?android:attr/textAppearanceMedium"
        android:text="Medium Text"
        android:id="@+id/textView3"
        android:layout_alignParentBottom="true"
        android:layout_marginTop="600dp"
        android:layout_alignParentRight="true"/>

    <ImageButton
        android:layout_width="30dp"
        android:layout_height="30dp"
        android:id="@+id/imageButton2"
        android:layout_alignParentLeft="true"
        android:onClick="back"
        android:layout_alignParentTop="true"
        android:src="@mipmap/back_button"/>
</RelativeLayout>

这是我的java代码：

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="16dp"
    android:paddingLeft="16dp"
    android:paddingRight="16dp"
    android:paddingTop="16dp"
    tools:context="com.example.zhenga1.photojewel.MainActivity">

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Start Accelerometer"
        android:id="@+id/button"
        android:onClick="start"
        android:layout_marginTop="300dp"
        android:layout_marginStart="0dp"
        android:layout_marginLeft="0dp"
        android:textStyle="normal"
        android:textSize="6pt"/>
    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="End Accelerometer"
        android:onClick="end"
        android:id="@+id/button2"
        android:layout_alignParentRight="true"
        android:layout_marginTop="300dp"
        android:textStyle="normal"
        android:textSize="6pt"/>

    <ImageView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/imageView2"
        android:layout_marginTop="200dp"
        android:layout_marginLeft="150dp"
        android:src="@mipmap/vibrator_pic"/>

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textAppearance="?android:attr/textAppearanceMedium"
        android:text="Medium Text"
        android:id="@+id/textView"
        android:layout_alignParentBottom="true"
        android:layout_marginTop="600dp"
        android:layout_marginLeft="0dp"
        android:layout_marginStart="0dp"/>

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textAppearance="?android:attr/textAppearanceMedium"
        android:text="Medium Text"
        android:id="@+id/textView2"
        android:layout_alignParentBottom="true"
        android:layout_centerHorizontal="true"/>

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textAppearance="?android:attr/textAppearanceMedium"
        android:text="Medium Text"
        android:id="@+id/textView3"
        android:layout_alignParentBottom="true"
        android:layout_marginTop="600dp"
        android:layout_alignParentRight="true"/>

    <ImageButton
        android:layout_width="30dp"
        android:layout_height="30dp"
        android:id="@+id/imageButton2"
        android:layout_alignParentLeft="true"
        android:onClick="back"
        android:layout_alignParentTop="true"
        android:src="@mipmap/back_button"/>
</RelativeLayout>

我已经研究了一些类似的错误，但它们都处理未正确初始化的按钮，这不是我的情况。请帮我。谢谢

Answer 1

在您的布局文件中，您的开始按钮的标识为R.id.button，在您的活动类中，您正在使用标识R.id.button1查找该视图。你的布局：

<Button
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="Start Accelerometer"
    android:id="@+id/button"  <--- HERE
    android:onClick="start"
    android:layout_marginTop="300dp"
    android:layout_marginStart="0dp"
    android:layout_marginLeft="0dp"
    android:textStyle="normal"
    android:textSize="6pt"/>

活动：

 start = (Button)findViewById(R.id.button1);

您需要在这两个地方设置相同的ID 。

Answer 2

即使您初始化了那些没有指向您的活动布局按钮的按钮，它也会在Android Studio

中发生。

代码错误：java.lang.IllegalStateException：无法执行android的方法：onClick

2 个答案: