android - 加速度计应用程序编码帮助？

Question

我正在编写一个应用程序来显示 Android 中加速度计在 X、Y 和 Z 方向上的值。我是 Android 菜鸟，所以请多多包涵。这是我的代码，它非常简单，但我收到一个空指针异常，我不确定我的代码有什么问题。谢谢!

package com.*****.accelo;

import android.app.Activity;

import android.content.Context;

import android.hardware.Sensor;

import android.hardware.SensorEvent;

import android.hardware.SensorEventListener;

import android.hardware.SensorManager;

import android.os.Bundle;

import android.widget.TextView;



public class AcceloActivity extends Activity implements SensorEventListener{



TextView textViewX, textViewY, textViewZ, textViewError;

StringBuilder builderx = new StringBuilder();
StringBuilder buildery = new StringBuilder();
StringBuilder builderz = new StringBuilder();




public void onCreate(Bundle savedInstanceState){

    super.onCreate(savedInstanceState);

    textViewError = (TextView) findViewById(R.id.textViewError);
    textViewX = (TextView) findViewById(R.id.textViewX);
    textViewY = (TextView) findViewById(R.id.textViewY);
    textViewX = (TextView) findViewById(R.id.textViewZ);




    SensorManager manager = (SensorManager) getSystemService(Context.SENSOR_SERVICE);

    Sensor accelerometer = manager.getDefaultSensor(Sensor.TYPE_ACCELEROMETER);

        if(!manager.registerListener(this, accelerometer,  
SensorManager.SENSOR_DELAY_UI)){
        setContentView(textViewError);

        }
}

public void onAccuracyChanged(Sensor sensor, int accuracy) {



}



public void onSensorChanged(SensorEvent event) {

    builderx.setLength(0);
    buildery.setLength(0);
    builderz.setLength(0);

    builderx.append("X " + event.values[0]);
    buildery.append("Y"+  event.values[1] );
    builderz.append("Z " + event.values[2]);

    textViewX.setText(builderx.toString());
    textViewY.setText(buildery.toString());
    textViewZ.setText(builderz.toString());

}



}

来自 logcat:

10-24 19:52:43.574: ERROR/AndroidRuntime(711): java.lang.RuntimeException: Unable to   
start activity ComponentInfo{com.amrit.accelo/com.amrit.accelo.AcceloActivity}: 
java.lang.NullPointerException
10-24 19:52:43.574: ERROR/AndroidRuntime(711):     at
android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1647)
10-24 19:52:43.574: ERROR/AndroidRuntime(711):     at 
android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1663)
10-24 19:52:43.574: ERROR/AndroidRuntime(711):     at  
android.app.ActivityThread.access$1500(ActivityThread.java:117)
10-24 19:52:43.574: ERROR/AndroidRuntime(711):     at     
android.app.ActivityThread$H.handleMessage(ActivityThread.java:931)
10-24 19:52:43.574: ERROR/AndroidRuntime(711):     at     
android.os.Handler.dispatchMessage(Handler.java:99)
10-24 19:52:43.574: ERROR/AndroidRuntime(711):     at 
android.os.Looper.loop(Looper.java:123)
10-24 19:52:43.574: ERROR/AndroidRuntime(711):     at   
android.app.ActivityThread.main(ActivityThread.java:3683)
10-24 19:52:43.574: ERROR/AndroidRuntime(711):     at      
java.lang.reflect.Method.invokeNative(Native Method)
10-24 19:52:43.574: ERROR/AndroidRuntime(711):     at    
java.lang.reflect.Method.invoke(Method.java:507)
10-24 19:52:43.574: ERROR/AndroidRuntime(711):     at   
com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
10-24 19:52:43.574: ERROR/AndroidRuntime(711):     at   
com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
10-24 19:52:43.574: ERROR/AndroidRuntime(711):     at   
dalvik.system.NativeStart.main(Native Method)
10-24 19:52:43.574: ERROR/AndroidRuntime(711): Caused by: java.lang.NullPointerException      
10-24 19:52:43.574: ERROR/AndroidRuntime(711):     at   
com.amrit.accelo.AcceloActivity.onCreate(AcceloActivity.java:50)
10-24 19:52:43.574: ERROR/AndroidRuntime(711):     at     
android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
10-24 19:52:43.574: ERROR/AndroidRuntime(711):     at   
android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1611)

谢谢!

Answer 1

您从第 50 行收到此错误:

textViewError.setText("错误，无法注册传感器监听器");

所以你的 textViewError 变量在这里是空的。您将需要创建一个 XML 布局，使用 setContentView，然后将 TextView 添加到您的 XML 布局，然后使用 findViewById 将您的 TextView 分配给它。 This is probably a good place to start .

编辑:

明确一点，您需要在调用 findViewById 之前设置内容 View 。

public void onCreate(Bundle savedInstanceState){

    super.onCreate(savedInstanceState);

    setContentView(R.layout.yourlayout);

    textViewError = (TextView) findViewById(R.id.textViewError);
    textViewX = (TextView) findViewById(R.id.textViewX);
    textViewY = (TextView) findViewById(R.id.textViewY);
    textViewX = (TextView) findViewById(R.id.textViewZ);
    ...

这里重要的是，您必须在 res/layout/ 下有一个名为 yourlayout.xml 的 xml 布局文件，其中包含您正在加载的 View 。