创建新项目符号时应用程序崩溃 [Andoid Studio]

Question

I'm trying to get my player to spawn a bullet every time I tap on the screen. However, every time I do so it crashes and gives me this error:

E/AndroidRuntime: FATAL EXCEPTION: Thread-3
    Process: com.example.mgp2021, PID: 20750
    java.lang.NullPointerException: Attempt to invoke virtual method 'int android.graphics.Bitmap.getWidth()' on a null object reference
        at com.example.mgp2021.Bullet.Render(Bullet.java:57)

Here is the bullet's script:

package com.example.spaceshooter;

import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.graphics.Matrix;
import android.util.DisplayMetrics;
import android.util.Log;
import android.view.SurfaceView;


public class Bullet implements EntityBase{
    private boolean isDone = false;
    private Bitmap bullet = null, scaledbmp = null;

    public float xPos = 0;
    public float yPos = 0;

    private float yLimit = 0;
    //float imgRadius = bullet.getHeight() * 0.5f;

    @Override
    public boolean IsDone() {
        return isDone;
    }

    @Override
    public void SetIsDone(boolean _isDone) {
        isDone = _isDone;
    }

    @Override
    public void Init(SurfaceView _view) {
        bullet = BitmapFactory.decodeResource(_view.getResources(), R.drawable.bullet);
        //setting up values
        xPos = DraggablePlayer.Instance.xPos;
        yPos = DraggablePlayer.Instance.yPos;
        //yLimit = _view.getHeight() * 0.5f;
    }


    @Override
    public void Update(float _dt) {
        yPos -= _dt * 300.f;

        if(bullet == null)
        {
            Log.e("ERR","Failed to decode resource bullet");
        }
    }

    @Override
    public void Render(Canvas _canvas) {
        Matrix transform = new Matrix();
        transform.postTranslate(-bullet.getWidth()*0.5f, -bullet.getHeight()*0.5f);
        transform.postTranslate(xPos, yPos);
        _canvas.drawBitmap(bullet, transform, null);
    }

    @Override
    public boolean IsInit() {
        return bullet != null;
    }

    @Override
    public int GetRenderLayer() {
        return LayerConstants.BULLET_LAYER;
    }

    @Override
    public void SetRenderLayer(int _newLayer) {
    }

    @Override
    public ENTITY_TYPE GetEntityType() {
        return ENTITY_TYPE.ENT_BULLET;
    }

    public static Bullet Create() {
        Bullet result = new Bullet();
        EntityManager.Instance.AddEntity(result, ENTITY_TYPE.ENT_BULLET);
        return result;
    }
}

and here is the script for when I spawn the bullets:

public void Update(float _dt) {

        EntityManager.Instance.Update(_dt);

       if (TouchManager.Instance.IsDown())
       {
            Bullet.Create();
       }
    }

I'm really unsure of what's causing this error, any help is greatly appreciated

Answer 1

The problem is that you call static Create method of your bullet class that return you an instance of Bullet but you never call (judging from code you posted) Init method that will actually read the contents of your R.drawable.bullet into a bitmap object.

Answer: Make sure you call Init before Render .

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Compare creation of Bullet object to creation of other objects that work in your app (I'm talking about objects implementing EntityBase ).