Question

好的，我试图让我的应用程序做的是以下内容。

打开时，显示一个开始按钮。
按下该按钮时，两个服务启动，一个用于加速计，一个用于GPS，按钮变为停止按钮。
服务将继续运行，直到按下停止按钮，关闭监听器并停止服务。
按下停止按钮后，应用程序会显示应用程序在收集数据时执行的一些计算。

要了解的重要事实：

所有计算工作
问题在我更改视图后开始，最初只有一个视图显示按钮和所有计算，因为它们实时更新。
然后我将应用更改为3次观看。每个按钮一个，结果一个。在我这样做之后，应用程序停止了工作。然而！！！！我可能已经做了一些更改而没有在我改变视图之前检查它们是否有效，但我一直试图弄清楚问题是什么，以至于我无法正确记住事件的确切顺序。

这是我当前的onCreate方法：

public void onCreate(Bundle savedInstanceState) {

    super.onCreate(savedInstanceState);
    setContentView(R.layout.start);

    setGPS();
    context = this;

    Button startButton = (Button) findViewById(R.id.startbutton);
    Button stopButton = (Button) findViewById(R.id.stopbutton);

    Log.d("NULL POINTER", "NULL POINTER");
    startButton.setOnClickListener(new View.OnClickListener() {
        public void onClick(View v) {
            Log.d("NULL POINTER", "NULL POINTER");
            //setContentView(R.layout.stop);
            startService();

        }
    });

    stopButton.setOnClickListener(new View.OnClickListener() {
        public void onClick(View v) {

            //setContentView(R.layout.results);
            stopService();

        }
    });

好的，在此代码中，您将看到两个Log.d打印件，上面写着“NULL POINTER”。当我运行我的代码时，第一个显示但第二个不显示，显然意味着中间的代码导致程序崩溃，这会显示在日志中：

06-15 12:30:25.176: DEBUG/AndroidRuntime(1037): >>>>>>>>>>>>>> AndroidRuntime START <<<<<<<<<<<<<<
06-15 12:30:25.185: DEBUG/AndroidRuntime(1037): CheckJNI is ON
06-15 12:30:25.537: DEBUG/AndroidRuntime(1037): --- registering native functions ---
06-15 12:30:25.806: DEBUG/ddm-heap(1037): Got feature list request
06-15 12:30:26.147: INFO/ActivityManager(52): Starting activity: Intent {act=android.intent.action.MAIN cat=[android.intent.category.LAUNCHER] flg=0x10000000 cmp=Hartford.gps/.GPSMain }
06-15 12:30:26.177: INFO/ActivityManager(52): Start proc Hartford.gps for activity Hartford.gps/.GPSMain: pid=1043 uid=10030 gids={}
06-15 12:30:26.196: DEBUG/AndroidRuntime(1037): Shutting down VM
06-15 12:30:26.196: DEBUG/dalvikvm(1037): DestroyJavaVM waiting for non-daemon threads to exit
06-15 12:30:26.196: DEBUG/dalvikvm(1037): DestroyJavaVM shutting VM down
06-15 12:30:26.196: DEBUG/dalvikvm(1037): HeapWorker thread shutting down
06-15 12:30:26.207: DEBUG/dalvikvm(1037): HeapWorker thread has shut down
06-15 12:30:26.207: DEBUG/jdwp(1037): JDWP shutting down net...
06-15 12:30:26.226: INFO/dalvikvm(1037): Debugger has detached; object registry had 1 entries
06-15 12:30:26.226: DEBUG/dalvikvm(1037): VM cleaning up
06-15 12:30:26.246: ERROR/AndroidRuntime(1037): ERROR: thread attach failed
06-15 12:30:26.317: DEBUG/dalvikvm(1037): LinearAlloc 0x0 used 638596 of 5242880 (12%)
06-15 12:30:26.456: DEBUG/ddm-heap(1043): Got feature list request
06-15 12:30:26.906: DEBUG/NULL POINTER(1043): NULL POINTER
06-15 12:30:26.916: DEBUG/AndroidRuntime(1043): Shutting down VM
06-15 12:30:26.916: WARN/dalvikvm(1043): threadid=3: thread exiting with uncaught exception (group=0x4001b188)
06-15 12:30:26.916: ERROR/AndroidRuntime(1043): Uncaught handler: thread main exiting due to uncaught exception
06-15 12:30:26.926: ERROR/AndroidRuntime(1043): java.lang.RuntimeException: Unable to start activity ComponentInfo{Hartford.gps/Hartford.gps.GPSMain}: java.lang.NullPointerException
06-15 12:30:26.926: ERROR/AndroidRuntime(1043):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2496)
06-15 12:30:26.926: ERROR/AndroidRuntime(1043):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2512)
06-15 12:30:26.926: ERROR/AndroidRuntime(1043):     at android.app.ActivityThread.access$2200(ActivityThread.java:119)
06-15 12:30:26.926: ERROR/AndroidRuntime(1043):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1863)
06-15 12:30:26.926: ERROR/AndroidRuntime(1043):     at android.os.Handler.dispatchMessage(Handler.java:99)
06-15 12:30:26.926: ERROR/AndroidRuntime(1043):     at android.os.Looper.loop(Looper.java:123)
06-15 12:30:26.926: ERROR/AndroidRuntime(1043):     at android.app.ActivityThread.main(ActivityThread.java:4363)
06-15 12:30:26.926: ERROR/AndroidRuntime(1043):     at java.lang.reflect.Method.invokeNative(Native Method)
06-15 12:30:26.926: ERROR/AndroidRuntime(1043):     at java.lang.reflect.Method.invoke(Method.java:521)
06-15 12:30:26.926: ERROR/AndroidRuntime(1043):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:860)
06-15 12:30:26.926: ERROR/AndroidRuntime(1043):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618)
06-15 12:30:26.926: ERROR/AndroidRuntime(1043):     at dalvik.system.NativeStart.main(Native Method)
06-15 12:30:26.926: ERROR/AndroidRuntime(1043): Caused by: java.lang.NullPointerException
06-15 12:30:26.926: ERROR/AndroidRuntime(1043):     at Hartford.gps.GPSMain.onCreate(GPSMain.java:70)
06-15 12:30:26.926: ERROR/AndroidRuntime(1043):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
06-15 12:30:26.926: ERROR/AndroidRuntime(1043):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2459)
06-15 12:30:26.926: ERROR/AndroidRuntime(1043):     ... 11 more

我在我的智慧结束时试图让它发挥作用！我已经尝试了所有我能想到的东西，但我认为在这个阶段我有视觉，只需要另一组眼睛来看它。

如果需要，我可以发布更多代码

任何人都可以提供任何帮助都很棒！

@ Mark

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    >
    <Button
        android:id="@+id/startbutton"
        android:layout_width="100px" 
        android:layout_height="100px" 
        android:text="Start"
        android:layout_centerInParent="true"
    />

</LinearLayout>

@ Egor和Mah

这里是标有

import java.text.DecimalFormat;
import java.text.NumberFormat;

import android.app.Activity;
import android.content.Context;
import android.content.Intent;
import android.os.Bundle;
import android.os.PowerManager;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
import android.widget.Toast;

public class GPSMain extends Activity   {

PowerManager powerManager;
PowerManager.WakeLock wL;

//text views to display latitude and longitude
static TextView latituteField;
static TextView longitudeField;
static TextView kmphSpeedField;
static TextView avgKmphField;
static TextView topKmphField;
static TextView accText;

//objects to store positional information
protected static double lat;
protected static double lon;

//objects to store values for current and average speed
protected static double kmphSpeed;
protected static double avgKmph;
protected static double totalKmph;
protected static double topKmph=0;

static String a, b, c;

private Context context;

//counter that is incremented every time a new position is received, used to calculate average speed
static int counter = 0;

/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {

    super.onCreate(savedInstanceState);
    setContentView(R.layout.start);

    setGPS();
    context = this;

    Button startButton = (Button) findViewById(R.id.startbutton);
    Button stopButton = (Button) findViewById(R.id.stopbutton);

    Log.d("NULL POINTER", "NULL POINTER");
    startButton.setOnClickListener(new View.OnClickListener() {
        public void onClick(View v) {
            Log.d("NULL POINTER", "NULL POINTER");
            //setContentView(R.layout.stop);
            startService();

        }
    });

70      stopButton.setOnClickListener(new View.OnClickListener() {
        public void onClick(View v) {

            //setContentView(R.layout.results);
            stopService();

        }
    });

    latituteField = (TextView) findViewById(R.id.lat);
    longitudeField = (TextView) findViewById(R.id.lon);     
    kmphSpeedField = (TextView) findViewById(R.id.kmph);
    avgKmphField = (TextView) findViewById(R.id.avgkmph);
    topKmphField = (TextView) findViewById(R.id.topkmph);
    accText = (TextView) findViewById(R.id.acctext);

}

void setGPS(){
    powerManager = (PowerManager)getSystemService(Context.POWER_SERVICE);
    wL = powerManager.newWakeLock(PowerManager.SCREEN_BRIGHT_WAKE_LOCK,"My Tag");

}

static String roundTwoDecimalFloat(float a){

    String formattedNum;
    NumberFormat nf = new DecimalFormat();
    nf.setMaximumFractionDigits(2);
    nf.setMinimumFractionDigits(2);
    formattedNum = nf.format(a);
    return formattedNum;
}

void startService(){

    wL.acquire();
    Log.d("DEBUG", "start");
    startService(new Intent(this, AccelerometerReader.class));
    Toast.makeText(context, "Accessing Accelerometer", Toast.LENGTH_LONG).show();
    //startService(new Intent(this, Calculations.class));
    //Toast.makeText(context, "Acquiring GPS Locations", Toast.LENGTH_LONG).show();

}

void stopService(){

    wL.release();
    Calculations.locationManager.removeUpdates(Calculations.locationListener);
    stopService(new Intent(this, AccelerometerReader.class));
    Toast.makeText(context, "Terminating Accelerometer", Toast.LENGTH_LONG).show();
    //stopService(new Intent(this, Calculations.class));
    //Toast.makeText(context, "Terminating Connection", Toast.LENGTH_LONG).show();

}

static void update(){

    latituteField.setText("Current Latitude: "+String.valueOf(lat));
    longitudeField.setText("Current Longitude: "+String.valueOf(lon));
    kmphSpeedField.setText("Cuttent Speed (kmph): "+String.valueOf(kmphSpeed));
    avgKmphField.setText("Average Speed (kmph): "+String.valueOf(avgKmph));
    topKmphField.setText("Top Speed (kmph): "+String.valueOf(topKmph));
    accText.setText("Accelerometer Values: "+" x: " + a + " y: " + b + " z: " + c);

}

}

Answer 1

你断言两个Log语句证明它们之间发生了错误。 onClick（）代码将在稍后执行。

导致错误的最可能原因是startButton或stopButton为空，并且您的findViewById次查找中的一个或两个都失败了。尝试在日志语句中转储它们，或者在调试器下运行它们并检查它们以查看哪个为空。

编辑：看到你的XML文件，现在问题很明显了。您正在膨胀start.xml，其中包含R.id.startbutton的定义。但它不包含R.id.stopbutton的定义。因此，Button stopButton = (Button) findViewById(R.id.stopbutton);将stopButton设置为null，因为它在您的布局中不存在。然后尝试将OnClickListener添加到此null对象，这会导致您的NPE。

onSetClickListener的空指针异常

1 个答案: