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

Question

我制作了一个 android 项目，它将启动一个加速度计传感器，并将传感器 x、y、z 数据存储在一个文件中。我在方法start 中添加了代码行start.setEnabled(false) 和stop.setEnabled(true)，此后我的代码在start 崩溃。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) 

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：

package com.example.zhenga1.photojewel;
import android.app.Activity;
import android.content.Context;
import android.hardware.Sensor;
import android.hardware.SensorEvent;

import java.lang.Boolean;
import java.io.File;
import android.hardware.SensorEventListener;
import android.hardware.SensorManager;
import android.os.Bundle;
import android.os.SystemClock;
import android.view.View;
import android.widget.Toast;
import android.widget.Button;
import android.widget.TextView;
import java.util.TimerTask;
import java.util.Timer;
import java.io.FileWriter;
import java.io.IOException;
import java.util.Arrays;
public class Main3Activity extends Activity implements SensorEventListener{
    private Sensor Accel;
    static private SensorManager Sensor;
    public float[] linear_acceleration;
    private float maxdeltax, maxdeltay, maxdeltaz;
    public float[] gravity;
    private Boolean bool = Boolean.TRUE;
    public float[] prevvalue;
    private float deltax, deltay, deltaz;
    private FileWriter prnt;
    private Timer timer;
    private TimerTask timerTask;
    private File fold, file;
    private Button start, stop;
    private TextView curx,cury,curz;
    private int count, curd;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main3);
        count = 0;
        initializetimer();
        System.out.println("This is the clock time in Mills"+SystemClock.uptimeMillis());
        linear_acceleration = new float[3];
        start = (Button)findViewById(R.id.button1);
        stop = (Button)findViewById(R.id.button2);
        maxdeltax = 0f;
        maxdeltay = 0f;
        maxdeltaz = 0f;
        gravity = new float[3];
        fold = new File("sdcard/vibration");
        if(!fold.exists()) {
            fold.mkdir();
        }
        file = new File("sdcard/vibration/data.txt");
        int v=0;
        if(!file.exists())
        {
            try {
                file.createNewFile();
            } catch (IOException e) {
                e.printStackTrace();
            }
            curd = 0;
        }
        else {
            while (file.exists()) {
                v++;
                file = new File("sdcard/vibration/data" + v + ".txt");
                curd = v;
            }
            int d = v-1;
            file = new File("sdcard/vibration/data"+d+".txt");
            if(file.length()>300)
            {
                file = new File("sdcard/vibration/data"+d+".txt");
                curd = d;
            }
            try {
                file.createNewFile();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        prevvalue = new float[3];
        Arrays.fill(prevvalue,0);
        Sensor = (SensorManager) getSystemService(Context.SENSOR_SERVICE);
        Accel = Sensor.getDefaultSensor(android.hardware.Sensor.TYPE_ACCELEROMETER);
        curx = (TextView)findViewById(R.id.textView);
        cury = (TextView)findViewById(R.id.textView2);
        curz = (TextView)findViewById(R.id.textView3);
        displayCurrentValues(0,0,0);

        try {
            prnt = new FileWriter(file, Boolean.TRUE);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
    private void initializetimer()
    {
        timerTask = new TimerTask() {
            @Override
            public void run() {
                saveCurVals(maxdeltax,maxdeltay,maxdeltaz);
                maxdeltax = 0f;
                maxdeltay = 0f;
                maxdeltaz = 0f;
            }
        };
    }
    public void start(View view)
    {
        stop.setEnabled(true);
        Sensor.registerListener(this, Accel, SensorManager.SENSOR_DELAY_NORMAL);
        timer = new Timer();
        timer.schedule(timerTask, 1000, 1000);
        start.setEnabled(false);
    }
    public void end(View view)
    {
        Sensor.unregisterListener(this);
        displayCurrentValues(0, 0, 0);
        try {
            prnt.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
        timer.cancel();
        stop.setEnabled(false);
        start.setEnabled(true);
    }

    @Override
    public void onSensorChanged(SensorEvent event) {
        deltax = Math.abs(event.values[0]-prevvalue[0]);
        deltay = Math.abs(event.values[1]-prevvalue[1]);
        deltaz = Math.abs(event.values[2]-prevvalue[2]);

        findMaxValues(deltax,deltay,deltax);
        if(Math.abs(deltax)<1)
        {
            deltax=0;
        }
        if(Math.abs(deltay)<1)
        {
            deltay=0;
        }
        if(Math.abs(deltaz)<1)
        {
            deltaz=0;
        }

        displayCurrentValues(deltax,deltay,deltaz);
        prevvalue[0] = event.values[0];
        prevvalue[1] = event.values[1];
        prevvalue[2] = event.values[2];


    }
    private void findMaxValues(float x, float y, float z)
    {
        if(maxdeltax < x)
        {
            maxdeltax = x;
        }
        if(maxdeltay < y)
        {
            maxdeltay = y;
        }
        if(maxdeltaz < z)
        {
            maxdeltaz = z;
        }
    }
    private void displayCurrentValues(float x, float y, float z)
    {
        curx.setText("x:"+Float.toString(x));
        cury.setText("y:"+Float.toString(y));
        curz.setText("z:"+Float.toString(z));
    }
    private void saveCurVals(float x, float y, float z)
    {
        count++;
        try
        {
            prnt.write(Float.toString(x) + " " + Float.toString(y) + " " + Float.toString(z) + "\n");
            prnt.flush();
        }catch (IOException e)
        {
            e.printStackTrace();
        }
        if(file.length()>300)
        {
            redefineFile();
        }
    }
    private void redefineFile()
    {
        int bigd = curd + 1;
        file = new File("sdcard/vibration/data"+bigd+".txt");
        curd = bigd;
        try {
            file.createNewFile();
            prnt = new FileWriter(file,Boolean.TRUE);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
    public void back(View view)
    {
        finish();
        try {
            prnt.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
    @Override
    public void onAccuracyChanged(Sensor sensor, int accuracy) {
        if(accuracy == SensorManager.SENSOR_STATUS_ACCURACY_HIGH)
        {
            Toast.makeText(getApplicationContext(),"GOOD QUALITY and ACCURACY SENSOR",Toast.LENGTH_LONG).show();
        }
    }

}

我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。 谢谢你

Answer 1

在您的布局文件中，您的开始按钮的 ID 为 R.id.button，而在您的活动类中，您使用 ID R.id.button1 找到该视图。 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);

您需要在两个位置设置相同的 ID。

Answer 2

即使你初始化了那些不指向你的活动布局按钮的按钮，我也会在Android Studio 中发生同样的情况