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我有以下代码，用于设置图像并在图像顶部绘制文本。但是我似乎无法让代码工作，我的程序以 NPE 退出（参见 CATLOG）。似乎 createImage 方法中的 setImageBitmap() 行导致了这种情况，但我似乎无法弄清楚原因。

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_editor);
    Intent intent = getIntent();
    int position = intent.getIntExtra("position", 0);
    Log.w("myApp", "" + position);
    final ImageView iv_ttx = (ImageView) findViewById(R.id.iv_ttx);
    final int[] imgSizeIds = new int[] { R.drawable.img1,
            R.drawable.img2, R.drawable.img3 };

    // Create Paint Object
    paint = new Paint();
    paint.setStyle(Paint.Style.FILL);
    paint.setColor(Color.BLUE);
    paint.setTextSize(75);

    // Create or Load Bitmap
    iv_ttx.setImageResource(imgSizeIds[position]);
    originalBitmap = BitmapFactory.decodeResource(getResources(),
            imgSizeIds[position]);
    image = originalBitmap.copy(Bitmap.Config.RGB_565, true);
    iv_ttx.setImageBitmap(image);
    et_top = (EditText) findViewById(R.id.top_txt);
    Button btntop = (Button) findViewById(R.id.btntop);

    // Set OnClickListeners
    btntop.setOnClickListener(new OnClickListener() {

        @Override
        public void onClick(View view) {
            String user_text = et_top.getText().toString();
            createImage(user_text);
        }
    });



    public Bitmap createImage(String user_text) {
    // canvas object with bitmap image as constructor
    Canvas canvas = new Canvas(image);
    canvas.drawText("" + user_text, 400, 400, paint);
    iv_ttx.setImageBitmap(image);
    return image;
}

现在对于有趣的部分，如果我删除 iv_ttx.setImageBitmap(image) 行，在我单击顶部按钮后大约 30 秒左右，文本似乎出现在图像顶部，或者如果我一直持续单击它，有什么想法吗？

目录：

09-06 22:14:39.197: E/AndroidRuntime(21242): FATAL EXCEPTION: main
09-06 22:14:39.197: E/AndroidRuntime(21242): java.lang.NullPointerException
09-06 22:14:39.197: E/AndroidRuntime(21242):    at com.meme.hdmeme.MemeEditor.createImage(MemeEditor.java:72)
09-06 22:14:39.197: E/AndroidRuntime(21242):    at com.meme.hdmeme.MemeEditor$1.onClick(MemeEditor.java:63)
09-06 22:14:39.197: E/AndroidRuntime(21242):    at android.view.View.performClick(View.java:4204)
09-06 22:14:39.197: E/AndroidRuntime(21242):    at android.view.View$PerformClick.run(View.java:17355)
09-06 22:14:39.197: E/AndroidRuntime(21242):    at android.os.Handler.handleCallback(Handler.java:725)
09-06 22:14:39.197: E/AndroidRuntime(21242):    at android.os.Handler.dispatchMessage(Handler.java:92)
09-06 22:14:39.197: E/AndroidRuntime(21242):    at android.os.Looper.loop(Looper.java:137)
09-06 22:14:39.197: E/AndroidRuntime(21242):    at android.app.ActivityThread.main(ActivityThread.java:5214)
09-06 22:14:39.197: E/AndroidRuntime(21242):    at java.lang.reflect.Method.invokeNative(Native Method)
09-06 22:14:39.197: E/AndroidRuntime(21242):    at java.lang.reflect.Method.invoke(Method.java:511)
09-06 22:14:39.197: E/AndroidRuntime(21242):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:795)
09-06 22:14:39.197: E/AndroidRuntime(21242):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:562)
09-06 22:14:39.197: E/AndroidRuntime(21242):    at dalvik.system.NativeStart.main(Native Method)
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2 回答 2

1 
final ImageView iv_ttx = (ImageView) findViewById(R.id.iv_ttx);

在 onCreate 中声明，因此iv_ttx在其他函数中可以为 null，因为它已声明但未初始化（是吗？）。删除final ImageView并iv_ttx成为班级成员。

于 2013-09-06T21:31:08.720 回答
1

声明ImageView iv_ttx为类成员。

   ImageView iv_ttx;
   @Override
   protected void onCreate(Bundle savedInstanceState) {
   super.onCreate(savedInstanceState);
   setContentView(R.layout.activity_editor);
   iv_ttx = (ImageView) findViewById(R.id.iv_ttx);
于 2013-09-06T21:32:29.133 回答