加速度計應用程序編碼幫助？

Question

我正在編寫一個應用程序，以在X，Y和Z方向顯示Android中的加速度計值。我是Android小白菜，請耐心等待。這裏是我的代碼，它很簡單，但我收到一個空指針異常，我不知道我的代碼有什麼問題。謝謝！

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()); 

} 



} 

從logcat的：

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) 

謝謝！

Answer 1

您是從線50收到此錯誤：

textViewError.setText("Error, could not register sensor listener");

所以你textViewError變量爲空在這裏。您將需要創建一個XML佈局，使用setContentView，然後將TextView添加到您的XML佈局，然後將其與findViewById一起分配給您的TextView。 This is probably a good place to start。

編輯：

只是要清楚，你需要調用findViewById之前設置的內容視圖。

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); 
    ... 

這裏重要的是，你必須有一個名爲yourlayout.xmlres/layout/下一個XML佈局文件，其中包含要載入的意見。