如何修复无法启动活动 ComponentInfo.....：java.lang.NullPointerException [重复]

Posted 2023-04-14

【中文标题】如何修复无法启动活动 ComponentInfo.....：java.lang.NullPointerException [重复]

【英文标题】：how to fix Unable to start activity ComponentInfo.....: java.lang.NullPointerException [duplicate]如何修复无法启动活动 ComponentInfo.....：java.lang.NullPointerException [重复]

【发布时间】：2017-04-10 15:52:59

【问题描述】：

我是安卓新手。 它的应用程序指向朝拜的方向。实际上我有 3 个类：main、GPS servive 和 RoseGPS（旋转针）。从那个主要活动类我想调用其他类的函数。添加 RoseGPS 时出现错误。帮我解决它。

主活动

public class GPSMainActivity extends Activity implements SensorListener
//public class GPSMainActivity extends Activity
TextView textView1,textView2,textView3,textView4;
AppService appService;
Context context;
double latMasjid, lonMasjid;
public  static double degree;
private RelativeLayout direcCantainer;
SensorManager sensorManager;
static final int sensor=SensorManager.SENSOR_ORIENTATION;
private RoseGPS rose;


@Override
protected void onCreate(Bundle savedInstanceState) 
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_gpsmain);
    textView1=(TextView) findViewById(R.id.tvAddress);
    textView2=(TextView) findViewById(R.id.tvDegree);
    textView3=(TextView)findViewById(R.id.tvLat);
    textView4=(TextView) findViewById(R.id.tvLong);
    appService=new AppService(GPSMainActivity.this);

    Location gpsLocation = appService.getLocation();
    if (gpsLocation != null) 
        latMasjid=gpsLocation.getLatitude();
        lonMasjid = gpsLocation.getLongitude();
        String resultLat = "Latitude: " + gpsLocation.getLatitude() +
                " Longitude: " + gpsLocation.getLongitude();
        textView4.setText(resultLat);
     else 
        textView3.setText("gagal");
    
    degree=bearing(latMasjid,lonMasjid,21.42243,39.82624);
    textView2.setText(String.format("%.2f", degree)+(char)0x00B0);

    direcCantainer=(RelativeLayout)findViewById(R.id.cantainer_layout);
    rose = new RoseGPS(context);
    direcCantainer.addView(rose);
    rose.invalidate();
    sensorManager=(SensorManager)getSystemService(context.SENSOR_SERVICE);       
  

protected double bearing(double startLat, double startLng, double endLat, double endLng)
    double longitude1 = startLng;
    double longitude2 = endLng;
    double latitude1 = Math.toRadians(startLat);
    double latitude2 = Math.toRadians(endLat);
    double longDiff= Math.toRadians(longitude2 - longitude1);
    double y= Math.sin(longDiff)* Math.cos(latitude2);
    double x= Math.cos(latitude1)* Math.sin(latitude2)- Math.sin(latitude1)* Math.cos(latitude2)* Math.cos(longDiff);

    return (Math.toDegrees(Math.atan2(y, x))+360)%360;


public void onSensorChanged(int sensor, float[] values)
    if(sensor != GPSMainActivity.sensor)
        return;
    int orientation = (int)values[0];
    rose.setDirections(orientation, orientation);


public void onAccuracyChanged(int sensor, int accuracy)

玫瑰GPS

public class RoseGPS extends View

GPSMainActivity fragment1GPSMainActivity = new GPSMainActivity();

private float directionNorth=0;
private float directionQibla=0;
private TextView bearingNorth, bearingQibla;
private String bearingNorthString, bearingQiblaString;
private DecimalFormat df = new DecimalFormat("0.000");
private Bitmap compassBackground, compassNeedle;
private Matrix rotateNeedle=new Matrix();
private int width=240;
private int height=240;
private float centre_x=width*0.5f;
private float centre_y=height*0.5f;

public RoseGPS(Context context)
    super(context);
    initCompassView();


public RoseGPS(Context context, AttributeSet attrs, int defStyle)
    super(context,attrs,defStyle);
    initCompassView();


public RoseGPS(Context context, AttributeSet attrs)
    super(context, attrs);
    initCompassView();


public void onMeasure(int widthMeasureSpec, int heightMeasureSpec)
    setMeasuredDimension(width,height);


private void initCompassView()
compassNeedle=BitmapFactory.decodeResource(getResources(), R.drawable.panah_36);
compassBackground=BitmapFactory.decodeResource(getResources(), R.drawable.kompas_72);
width=compassBackground.getWidth()*2;
height=compassBackground.getHeight()*2;

centre_x=width*0.5f;
centre_y=height*0.5f;
rotateNeedle.postTranslate(centre_x - compassNeedle.getWidth()/2, centre_y - compassNeedle.getHeight()/2);
invalidate();


public void setConstants(TextView bearingNorth, CharSequence bearingNorthString, TextView bearingQibla, CharSequence bearingQiblaString)
    this.bearingNorth=bearingNorth;
    this.bearingNorthString=bearingNorthString.toString();
    this.bearingQibla=bearingQibla;
    this.bearingQiblaString=bearingQiblaString.toString();


public void setDirections(float directionsNorth, float directionsQibla)
    this.directionNorth=directionsNorth;
    this.directionQibla=directionsQibla;
    rotateNeedle=new Matrix();
    float degree=(float) GPSMainActivity.degree;

    rotateNeedle.postRotate(degree, compassNeedle.getWidth()/2, compassNeedle.getHeight()/2);
    rotateNeedle.postTranslate(centre_x - compassNeedle.getWidth()/2, centre_y - compassNeedle.getHeight()/2);
    invalidate();


protected void onDraw(Canvas canvas)
    bearingNorth.setText(bearingNorthString.replace("(1)", df.format(directionNorth)));
    bearingQibla.setText(bearingQiblaString.replace("(+/-)", directionQibla>=0 ? "+" : "-").replace("(2)", df.format(Math.abs(directionQibla))).replace("(3)", df.format(directionNorth+directionQibla)));

    Paint p=new Paint();
    canvas.rotate(-directionNorth, centre_x, centre_y);
    canvas.drawBitmap(compassBackground, compassBackground.getWidth()/2, compassBackground.getHeight()/2, p);
    canvas.drawBitmap(compassNeedle, rotateNeedle, p);

我的 xml

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_
android:layout_
android:orientation="vertical"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context="com.gpsaja.GPSMainActivity" >

<TextView
    android:id="@+id/tvAddress"
    android:layout_
    android:layout_
    android:text="@string/hello_world" 
    android:layout_gravity="center"
    android:textStyle="bold"/>

 <RelativeLayout
    android:id="@+id/cantainer_layout"
    android:layout_
    android:layout_
    android:background="#ffffff"
    android:layout_gravity="center">
    </RelativeLayout>

<TextView
    android:id="@+id/tvDegree"
    android:layout_
    android:layout_
    android:layout_gravity="center"
    android:text="@string/idDegree"
    android:textSize="20sp"
    android:textStyle="bold" />

<LinearLayout 
    android:layout_
    android:layout_
    android:layout_gravity="center"
    android:orientation="horizontal"
    >

    <TextView
        android:id="@+id/tvLat"
        android:layout_
        android:layout_
        android:text="@string/idLat" 
        android:gravity="center"/>

    <TextView
        android:id="@+id/tvLong"
        android:layout_
        android:layout_
        android:gravity="center"
        android:text="@string/idLon" />
</LinearLayout>

我的日志猫

 11-24 02:04:51.663: E/AndroidRuntime(2177): FATAL EXCEPTION: main
11-24 02:04:51.663: E/AndroidRuntime(2177): Process: com.gpsaja, PID: 2177
11-24 02:04:51.663: E/AndroidRuntime(2177): java.lang.RuntimeException: Unable to start activity ComponentInfocom.gpsaja/com.gpsaja.GPSMainActivity: java.lang.NullPointerException
11-24 02:04:51.663: E/AndroidRuntime(2177):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2184)
11-24 02:04:51.663: E/AndroidRuntime(2177):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2233)
11-24 02:04:51.663: E/AndroidRuntime(2177):     at android.app.ActivityThread.access$800(ActivityThread.java:135)
11-24 02:04:51.663: E/AndroidRuntime(2177):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
11-24 02:04:51.663: E/AndroidRuntime(2177):     at android.os.Handler.dispatchMessage(Handler.java:102)
11-24 02:04:51.663: E/AndroidRuntime(2177):     at android.os.Looper.loop(Looper.java:136)
11-24 02:04:51.663: E/AndroidRuntime(2177):     at android.app.ActivityThread.main(ActivityThread.java:5001)
11-24 02:04:51.663: E/AndroidRuntime(2177):     at java.lang.reflect.Method.invokeNative(Native Method)
11-24 02:04:51.663: E/AndroidRuntime(2177):     at java.lang.reflect.Method.invoke(Method.java:515)
11-24 02:04:51.663: E/AndroidRuntime(2177):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785)
11-24 02:04:51.663: E/AndroidRuntime(2177):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601)
11-24 02:04:51.663: E/AndroidRuntime(2177):     at dalvik.system.NativeStart.main(Native Method)
11-24 02:04:51.663: E/AndroidRuntime(2177): Caused by: java.lang.NullPointerException
11-24 02:04:51.663: E/AndroidRuntime(2177):     at android.view.ViewConfiguration.get(ViewConfiguration.java:352)
11-24 02:04:51.663: E/AndroidRuntime(2177):     at android.view.View.<init>(View.java:3448)
11-24 02:04:51.663: E/AndroidRuntime(2177):     at com.gpsaja.RoseGPS.<init>(RoseGPS.java:33)
11-24 02:04:51.663: E/AndroidRuntime(2177):     at com.gpsaja.GPSMainActivity.onCreate(GPSMainActivity.java:64)
11-24 02:04:51.663: E/AndroidRuntime(2177):     at android.app.Activity.performCreate(Activity.java:5231)
11-24 02:04:51.663: E/AndroidRuntime(2177):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
11-24 02:04:51.663: E/AndroidRuntime(2177):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2148)
11-24 02:04:51.663: E/AndroidRuntime(2177):     ... 11 more

【问题讨论】：

显然你不能这样做new GPSMainActivity()

【参考方案1】：

rose = new RoseGPS(context);

context 是 null。从您的代码中删除 context 字段。然后，将此行更改为：

rose = new RoseGPS(this);

由于Activity 继承自Context，因此您需要为活动创建小部件，并将活动用作Context。