無法打開由以下原因引起的活動：java.lang.NullPointerException

Question

我正在開發根據字母筆劃繪製字母表的應用程序。我無法運行DrawingActivity，因爲java.lang.NullPointerException.I在編碼方面不夠強大。我覺得空錯誤來自getIntent().getExtras().getString("type");。因此，我將代碼更改爲getIntent().getStringExtra("type");，但仍然無法運行DrawingActivity。請幫助我們。真的很感激它。

這是我的錯誤的logcat：

12-05 23:47:29.498 9620-9620/com.example.user.mygame E/AndroidRuntime: FATAL EXCEPTION: main 
                     Process: com.example.user.mygame, PID: 9620 
                     java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.user.mygame/com.example.user.mygame.DrawingActivity}: java.lang.NullPointerException 
                      at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2198) 
                      at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2247) 
                      at android.app.ActivityThread.access$800(ActivityThread.java:141) 
                      at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1210) 
                      at android.os.Handler.dispatchMessage(Handler.java:102) 
                      at android.os.Looper.loop(Looper.java:136) 
                      at android.app.ActivityThread.main(ActivityThread.java:5111) 
                      at java.lang.reflect.Method.invokeNative(Native Method) 
                      at java.lang.reflect.Method.invoke(Method.java:515) 
                      at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:806) 
                      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:622) 
                      at dalvik.system.NativeStart.main(Native Method) 
                     Caused by: java.lang.NullPointerException 
                      at com.example.user.mygame.DrawingActivity.onCreate(DrawingActivity.java:156) 
                      at android.app.Activity.performCreate(Activity.java:5248) 
                      at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087) 
                      at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2162) 
                      at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2247)  
                      at android.app.ActivityThread.access$800(ActivityThread.java:141)  
                      at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1210)  
                      at android.os.Handler.dispatchMessage(Handler.java:102)  
                      at android.os.Looper.loop(Looper.java:136)  
                      at android.app.ActivityThread.main(ActivityThread.java:5111)  
                      at java.lang.reflect.Method.invokeNative(Native Method)  
                      at java.lang.reflect.Method.invoke(Method.java:515)  
                      at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:806)  
                      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:622)  
                      at dalvik.system.NativeStart.main(Native Method)  

這是我DrawingActivity.java：

package com.example.user.mygame; 

import android.app.Activity; 
import android.content.Context; 
import android.graphics.Bitmap; 
import android.graphics.Bitmap.Config; 
import android.graphics.BitmapFactory; 
import android.graphics.Canvas; 
import android.graphics.Color; 
import android.graphics.Paint; 
import android.graphics.Paint.Cap; 
import android.graphics.Paint.Join; 
import android.graphics.Paint.Style; 
import android.graphics.Path; 
import android.graphics.Path.Direction; 
import android.graphics.Rect; 
import android.os.Bundle; 
import android.view.MotionEvent; 
import android.view.View; 
import android.view.View.OnClickListener; 
import android.view.View.OnTouchListener; 
import android.view.ViewGroup; 
import android.widget.ImageView; 
import android.widget.RelativeLayout.LayoutParams; 
import com.google.android.gms.location.DetectedActivity; 
import com.google.android.gms.maps.model.BitmapDescriptorFactory; 

public class DrawingActivity extends Activity implements OnClickListener, OnTouchListener { 

    View drawingView; 
    DrawingView dv; 
    LayoutParams params; 
    ViewGroup parent; 
    ImageView nextBtn; 
    ImageView playBtn; 
    ImageView prevBtn; 
    private Paint mPaint; 
    private Integer position; 
    private int totalItem; 
    private String type; 

    public class DrawingView extends View { 
     private static final float TOUCH_TOLERANCE = 4.0f; 
     private Bitmap bm; 
     private Paint circlePaint; 
     private Path circlePath; 
     Context context; 
     private Bitmap mBitmap; 
     private Paint mBitmapPaint; 
     private Canvas mCanvas; 
     private Path mPath; 
     private float mX; 
     private float mY; 

     public DrawingView(Context c) { 
      super(c); 
      this.context = c; 
      this.mPath = new Path(); 
      this.mBitmapPaint = new Paint(4); 
      this.circlePaint = new Paint(); 
      this.circlePath = new Path(); 
      this.circlePaint.setAntiAlias(true); 
      this.circlePaint.setColor(Color.BLACK); 
      this.circlePaint.setStyle(Style.STROKE); 
      this.circlePaint.setStrokeJoin(Join.MITER); 
      this.circlePaint.setStrokeWidth(TOUCH_TOLERANCE); 
     } 

     protected void onSizeChanged(int w, int h, int oldw, int oldh) { 
      super.onSizeChanged(w, h, oldw, oldh); 
      this.mBitmap = Bitmap.createBitmap(w, h, Config.ARGB_8888); 
      this.mCanvas = new Canvas(this.mBitmap); 
      if (DrawingActivity.this.type.equals(Resource.DRAWING_ALPHABET)) { 
       this.bm = BitmapFactory.decodeResource(getResources(), Resource.capitalStoke[DrawingActivity.this.position]); 
      } 
      this.mCanvas.drawBitmap(this.bm, new Rect(0, 0, this.bm.getWidth(), this.bm.getHeight()), new Rect(0, 0, this.mCanvas.getWidth(), this.mCanvas.getHeight()), this.mBitmapPaint); 
     } 

     protected void onDraw(Canvas canvas) { 
      super.onDraw(canvas); 
      canvas.drawBitmap(this.mBitmap, 0.0f, 0.0f, this.mBitmapPaint); 
      canvas.drawPath(this.mPath, DrawingActivity.this.mPaint); 
      canvas.drawPath(this.circlePath, this.circlePaint); 
     } 

     private void touch_start(float x, float y) { 
      this.mPath.reset(); 
      this.mPath.moveTo(x, y); 
      this.mX = x; 
      this.mY = y; 
     } 

     private void touch_move(float x, float y) { 
      float dx = Math.abs(x - this.mX); 
      float dy = Math.abs(y - this.mY); 
      if (dx >= TOUCH_TOLERANCE || dy >= TOUCH_TOLERANCE) { 
       this.mPath.quadTo(this.mX, this.mY, (this.mX + x)/2.0f, (this.mY + y)/2.0f); 
       this.mX = x; 
       this.mY = y; 
       this.circlePath.reset(); 
       this.circlePath.addCircle(this.mX, this.mY, BitmapDescriptorFactory.HUE_ORANGE, Direction.CW); 
      } 
     } 

     private void touch_up() { 
      this.mPath.lineTo(this.mX, this.mY); 
      this.circlePath.reset(); 
      this.mCanvas.drawPath(this.mPath, DrawingActivity.this.mPaint); 
      this.mPath.reset(); 
     } 

     public boolean onTouchEvent(MotionEvent event) { 
      float x = event.getX(); 
      float y = event.getY(); 
      switch (event.getAction()) { 
       case DetectedActivity.IN_VEHICLE /*0*/: 
        touch_start(x, y); 
        invalidate(); 
        break; 
       case DetectedActivity.ON_BICYCLE /*1*/: 
        touch_up(); 
        invalidate(); 
        break; 
       case DetectedActivity.ON_FOOT /*2*/: 
        touch_move(x, y); 
        invalidate(); 
        break; 
      } 
      return true; 
     } 

     public void resetCanvas() { 
      this.bm = null; 
      this.mBitmap = null; 
      System.gc(); 
     } 
    } 

    public DrawingActivity() { 
     this.type = ""; 
     this.position = 0; 
     this.totalItem = 0; 

     this.nextBtn = null; 
     this.playBtn = null; 
     this.prevBtn = null; 
     this.drawingView = null; 
     this.parent = null; 
     this.params = null; 
    } 

    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     requestWindowFeature(1); 
     setContentView(R.layout.drawing_alphabet); 
     this.type = getIntent().getExtras().getString("type"); 
     this.nextBtn = (ImageView) findViewById(R.id.nextId); 
     this.playBtn = (ImageView) findViewById(R.id.playId); 
     this.prevBtn = (ImageView) findViewById(R.id.prevId); 
     this.nextBtn.setOnClickListener(this); 
     this.nextBtn.setOnTouchListener(this); 
     this.prevBtn.setOnClickListener(this); 
     this.prevBtn.setOnTouchListener(this); 
     this.playBtn.setOnClickListener(this); 
     this.playBtn.setOnTouchListener(this); 
     this.drawingView = findViewById(R.id.drawingViewId); 
     this.params = (LayoutParams) this.drawingView.getLayoutParams(); 
     this.dv = new DrawingView(this); 
     this.dv.setLayoutParams(this.params); 
     this.parent = (ViewGroup) this.drawingView.getParent(); 
     int index = this.parent.indexOfChild(this.drawingView); 
     this.parent.removeView(this.drawingView); 
     this.parent.addView(this.dv, index); 
     if (this.type.equals(Resource.DRAWING_ALPHABET)) { 
      this.totalItem = Resource.capitalStoke.length; 
     } 
     this.mPaint = new Paint(); 
     this.mPaint.setAntiAlias(true); 
     this.mPaint.setDither(true); 
     this.mPaint.setColor(Color.BLACK); 
     this.mPaint.setStyle(Style.STROKE); 
     this.mPaint.setStrokeJoin(Join.ROUND); 
     this.mPaint.setStrokeCap(Cap.ROUND); 
     this.mPaint.setStrokeWidth(16.0f); 
     updatePreviousButton(); 
    } 


    public boolean onTouch(View v, MotionEvent event) { 
     switch (event.getAction()) { 
      case DetectedActivity.IN_VEHICLE /*0*/: 
       if (v.getId() == R.id.nextId || v.getId() == R.id.playId || v.getId() == R.id.prevId) { 
        v.setAlpha(0.5f); 
        break; 
       } 
      case DetectedActivity.ON_BICYCLE /*1*/: 
       if (v.getId() == R.id.nextId || v.getId() == R.id.playId || v.getId() == R.id.prevId) { 
        v.setAlpha(1.0f); 
        break; 
       } 
     } 
     return false; 
    } 

    public void onClick(View v) { 
     switch (v.getId()) { 
      case R.id.nextId: 
       this.position = this.position + 1; 
       changeStroke(); 
      case R.id.playId: 
       changeStroke(); 
      case R.id.prevId: 
       this.position = this.position - 1; 
       changeStroke(); 
      default: 
     } 
    } 

    private void changeStroke() { 
     updateNextButton(); 
     updatePreviousButton(); 
     int index = this.parent.indexOfChild(this.dv); 
     this.dv.resetCanvas(); 
     this.dv = null; 
     this.parent.removeViewAt(index); 
     this.dv = new DrawingView(this); 
     this.dv.setLayoutParams(this.params); 
     this.parent.addView(this.dv, index); 
    } 

    private void updateNextButton() { 
     if (this.position == this.totalItem - 1) { 
      this.nextBtn.setAlpha(0.5f); 
      this.nextBtn.setClickable(false); 
      return; 
     } 
     this.nextBtn.setAlpha(1.0f); 
     this.nextBtn.setClickable(true); 
    } 

    private void updatePreviousButton() { 
     if (this.position == 0) { 
      this.prevBtn.setAlpha(0.5f); 
      this.prevBtn.setClickable(false); 
      return; 
     } 
     this.prevBtn.setAlpha(1.0f); 
     this.prevBtn.setClickable(true); 
    } 
} 

這是我drawing_alphabet.xml：

<?xml version="1.0" encoding="utf-8"?> 
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" 
    android:layout_width="match_parent" 
    android:layout_height="match_parent" 
    android:background="@drawable/bg_drawing"> 
    <View 
     android:id="@+id/drawingViewId" 
     android:layout_width="wrap_content" 
     android:layout_height="wrap_content" 
     android:layout_marginLeft="0dp" 
     android:layout_marginRight="64dp" 
     android:layout_marginEnd="64dp"/> 
     <ImageView 
      android:id="@+id/prevId" 
      android:layout_width="52dp" 
      android:layout_height="52dp" 
      android:src="@drawable/back_icon" 
      android:layout_gravity="top" 
      android:layout_marginTop="49dp" 
      android:layout_alignParentTop="true" 
      android:layout_alignLeft="@+id/nextId" 
      android:layout_alignStart="@+id/nextId" /> 
     <ImageView 
      android:id="@+id/nextId" 
      android:layout_width="52dp" 
      android:layout_height="52dp" 
      android:src="@drawable/next_icon" 
      android:layout_gravity="bottom" 
      android:layout_marginTop="61dp" 
      android:layout_below="@+id/prevId" 
      android:layout_alignParentRight="true" 
      android:layout_alignParentEnd="true" />/

</RelativeLayout> 

這是我的清單。 xml：

<?xml version="1.0" encoding="utf-8"?> 
<manifest xmlns:android="http://schemas.android.com/apk/res/android" 
    package="com.example.user.mygame"> 

    <application 
     android:allowBackup="false" 
     android:icon="@mipmap/ic_launcher" 
     android:label="@string/app_name" 
     android:supportsRtl="true" 
     android:theme="@style/AppTheme" 
     android:name="android.support.multidex.MultiDexApplication"> 
     <activity android:name=".MainActivity" 
      android:screenOrientation="landscape"> 
      <intent-filter> 
       <action android:name="android.intent.action.MAIN" /> 
       <category android:name="android.intent.category.LAUNCHER" /> 
      </intent-filter> 
     </activity> 
     <activity android:label="@string/app_name" android:name="com.example.user.mygame.AlphabetActivity" android:screenOrientation="landscape" /> 
     <activity android:label="@string/app_name" android:name="com.example.user.mygame.DrawingActivity" android:screenOrientation="landscape" /> 
    </application> 

</manifest> 

這是我resource.java：

package com.example.user.mygame; 


public class Resource { 

    public static String DRAWING_ALPHABET; 
    public static Integer[] capitalStoke; 
    Integer[] alphabetCapital; 
    Integer[] alphabetSound; 
    Integer[] alphabetImage; 

    static { 
     DRAWING_ALPHABET = "alphabet"; 
     setCapitalStoke(new Integer[]{Integer.valueOf(R.drawable.capital_letters_stroke_01), 
       Integer.valueOf(R.drawable.capital_letters_stroke_02), 
       Integer.valueOf(R.drawable.capital_letters_stroke_03), 
       Integer.valueOf(R.drawable.capital_letters_stroke_04), 
       Integer.valueOf(R.drawable.capital_letters_stroke_05), 
       Integer.valueOf(R.drawable.capital_letters_stroke_06), 
       Integer.valueOf(R.drawable.capital_letters_stroke_07), 
       Integer.valueOf(R.drawable.capital_letters_stroke_08), 
       Integer.valueOf(R.drawable.capital_letters_stroke_09), 
       Integer.valueOf(R.drawable.capital_letters_stroke_10), 
       Integer.valueOf(R.drawable.capital_letters_stroke_11), 
       Integer.valueOf(R.drawable.capital_letters_stroke_12), 
       Integer.valueOf(R.drawable.capital_letters_stroke_13), 
       Integer.valueOf(R.drawable.capital_letters_stroke_14), 
       Integer.valueOf(R.drawable.capital_letters_stroke_15), 
       Integer.valueOf(R.drawable.capital_letters_stroke_16), 
       Integer.valueOf(R.drawable.capital_letters_stroke_17), 
       Integer.valueOf(R.drawable.capital_letters_stroke_18), 
       Integer.valueOf(R.drawable.capital_letters_stroke_19), 
       Integer.valueOf(R.drawable.capital_letters_stroke_20), 
       Integer.valueOf(R.drawable.capital_letters_stroke_21), 
       Integer.valueOf(R.drawable.capital_letters_stroke_22), 
       Integer.valueOf(R.drawable.capital_letters_stroke_23), 
       Integer.valueOf(R.drawable.capital_letters_stroke_24), 
       Integer.valueOf(R.drawable.capital_letters_stroke_25), 
       Integer.valueOf(R.drawable.capital_letters_stroke_26)}); 

    } 

    public static Integer[] getCapitalStoke() { 
     return capitalStoke; 
    } 
    public static void setCapitalStoke(Integer[] capitalStoke) { 
     Resource.capitalStoke = capitalStoke; 
    } 

    public Resource() { 
     this.alphabetCapital = new Integer[]{ 
       Integer.valueOf(R.drawable.img_letter_001), 
       Integer.valueOf(R.drawable.img_letter_002), 
       Integer.valueOf(R.drawable.img_letter_003), 
       Integer.valueOf(R.drawable.img_letter_004), 
       Integer.valueOf(R.drawable.img_letter_005), 
       Integer.valueOf(R.drawable.img_letter_006), 
       Integer.valueOf(R.drawable.img_letter_007), 
       Integer.valueOf(R.drawable.img_letter_008), 
       Integer.valueOf(R.drawable.img_letter_009), 
       Integer.valueOf(R.drawable.img_letter_010), 
       Integer.valueOf(R.drawable.img_letter_011), 
       Integer.valueOf(R.drawable.img_letter_012), 
       Integer.valueOf(R.drawable.img_letter_013), 
       Integer.valueOf(R.drawable.img_letter_014), 
       Integer.valueOf(R.drawable.img_letter_015), 
       Integer.valueOf(R.drawable.img_letter_016), 
       Integer.valueOf(R.drawable.img_letter_017), 
       Integer.valueOf(R.drawable.img_letter_018), 
       Integer.valueOf(R.drawable.img_letter_019), 
       Integer.valueOf(R.drawable.img_letter_020), 
       Integer.valueOf(R.drawable.img_letter_021), 
       Integer.valueOf(R.drawable.img_letter_022), 
       Integer.valueOf(R.drawable.img_letter_023), 
       Integer.valueOf(R.drawable.img_letter_024), 
       Integer.valueOf(R.drawable.img_letter_025), 
       Integer.valueOf(R.drawable.img_letter_026)}; 

     this.alphabetSound = new Integer[]{ 
       Integer.valueOf(R.raw.snd_a), 
       Integer.valueOf(R.raw.snd_b), 
       Integer.valueOf(R.raw.snd_c),}; 

     this.alphabetImage = new Integer[]{ 
       Integer.valueOf(R.drawable.image_1), 
       Integer.valueOf(R.drawable.image_2), 
       Integer.valueOf(R.drawable.image_3)}; 
    } 

} 

Answer 1

像NullPointerException異常指出，你的錯誤似乎是在onCreate方法命名DrawingActivity文件中的行156。

this.type = getIntent().getExtras().getString("type"); 

我相信這是被斷層，請仔細檢查正在發送你在這裏創建「類型」作爲它的值的意圖活動線路。

Answer 2

在活動通話DrawingActivity，你有沒有設置

Intent intent = new Intent(context, DrawingActivity.class); 
intent.putExtra("type","anyString"); // don't forget this line 
startActivity(intent);