奇怪（無效？）stacktrace在android中？

Question

這可能更多的是好奇心，而不是解決問題的願望，因爲它似乎是隨機發生的，只有一次。不過，也許它可能會讓我們對java或android的一些模糊的方面有所瞭解。

我們使用Lightstreamer庫，本質上它是一個流式庫，爲此我們註冊一個簡單的監聽器，只要流提供新值，就會調用該監聽器。

我在應用程序中遇到了異常，並檢查了logcat中的堆棧跟蹤。我無法弄清楚那裏發生了什麼。這裏是微量的（相關）頂部：

11-25 15:06:50.770 E/AndroidRuntime(3100): FATAL EXCEPTION: main 
11-25 15:06:50.770 E/AndroidRuntime(3100): java.lang.NullPointerException 
11-25 15:06:50.770 E/AndroidRuntime(3100):  at com.lightstreamer.ls_client.UpdateInfoImpl.getNewValue(UpdateInfoImpl.java:142) 
11-25 15:06:50.770 E/AndroidRuntime(3100):  at com.ourapp.view.ShrinkingTextViewHelper.onMeasure(ShrinkingTextViewHelper.java:30) 
11-25 15:06:50.770 E/AndroidRuntime(3100):  at com.ourapp.view.ButtonEx.onMeasure(ButtonEx.java:67) 
11-25 15:06:50.770 E/AndroidRuntime(3100):  at android.view.View.measure(View.java:10828) 

這裏是在其整體ShrinkingTextViewHelper.java：

package com.ourapp.view; 

import android.text.TextPaint; 
import android.text.TextUtils.TruncateAt; 

/** 
* Check text size on view and change the text size if it's width not fit to control's width 
* 
*/ 
public class ShrinkingTextViewHelper { 
    public static void onMeasure(ShrinkingTextView view, int widthMeasureSpec, int heightMeasureSpec) { 
     CharSequence text = view.getText(); 
     view.onMeasureSuper(widthMeasureSpec, heightMeasureSpec); 

     TextPaint paint = view.getPaint(); 

     float paddings = view.getPaddingLeft() + view.getPaddingRight(); 

     paint.setTextSize(view.getInitialTextSize()); 

     float size = paint.getTextSize(); 
     while (size >= view.getMinTextSize() 
       && paddings + paint.measureText(text, 0, text.length()) > view.getMeasuredTextWidth() 
       && (view.getLineCount() == 1 || view.getLineCount() > view.getMaxLines())) { 
      paint.setTextSize(--size); 
      view.setText(text); 
      view.onMeasureSuper(widthMeasureSpec, heightMeasureSpec); 
     } 

line 30:if (paddings + paint.measureText(text, 0, text.length()) > view.getMeasuredTextWidth()) { 
      view.setEllipsize(TruncateAt.END); 
     } 
    } 
} 

這是ButtonEx類也存在於堆棧跟蹤：

package com.ourapp.view; 

import android.content.Context; 
import android.content.res.TypedArray; 
import android.text.method.SingleLineTransformationMethod; 
import android.util.AttributeSet; 
import android.widget.Button; 

import com.ourapp.R; 
/** 
* Extended button class. It could shrink text on the face. 
* 
*/ 
public class ButtonEx extends Button implements ShrinkingTextView { 
    private static final float DEFAULT_MIN_TEXT_SIZE_DP = 10; 

    private float minTextSizePx; 
    private float initialTextSize; 
    private int maxLines; 

    /** 
    * Class constructor 
    * @param context 
    * @param attrs 
    */ 
    public ButtonEx(Context context, AttributeSet attrs) { 
     super(context, attrs); 

     TypedArray t = getContext().obtainStyledAttributes(attrs, R.styleable.ButtonEx); 
     minTextSizePx = t.getDimension(R.styleable.ButtonEx_minTextSize, dipToPixels(DEFAULT_MIN_TEXT_SIZE_DP)); 

     t.recycle(); 

     int att[] = new int[] { android.R.attr.singleLine }; 
     t = getContext().obtainStyledAttributes(attrs, att); 
     boolean singleLine = t.getBoolean(0, true); 
     boolean hasSingleLine = t.hasValue(0); 
     t.recycle(); 

     att = new int[] { android.R.attr.maxLines }; 
     t = getContext().obtainStyledAttributes(attrs, att); 

     boolean hasMaxLines = t.hasValue(0); 

     if (singleLine && hasSingleLine) { 
      maxLines = 1; 
     } else { 
      maxLines = t.getInteger(0, 1); 
     } 

     if (singleLine && hasSingleLine 
       || !hasSingleLine && !hasMaxLines) { 
      setTransformationMethod(new SingleLineTransformationMethod()); 
     } 

     setMaxLines(maxLines); 
     t.recycle(); 

     att = new int[] { android.R.attr.textSize }; 
     t = getContext().obtainStyledAttributes(attrs, att); 
     initialTextSize = t.getDimension(0, 0); 
     t.recycle(); 
    } 

    @Override 
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) { 
     ShrinkingTextViewHelper.onMeasure(this, widthMeasureSpec, heightMeasureSpec); 
    } 

    private float dipToPixels(float dip) { 
     return dip * getContext().getResources().getDisplayMetrics().density; 
    } 

    /** 
    * Get min size of text on title. 
    */ 
    public float getMinTextSize() { 
     return minTextSizePx; 
    } 

    /** 
    * Called to determine the size requirements for this view and all of its children. 
    */ 
    public void onMeasureSuper(int widthMeasureSpec, int heightMeasureSpec) { 
     super.onMeasure(widthMeasureSpec, heightMeasureSpec); 
    } 

    /** 
    * Get text width 
    */ 
    public int getMeasuredTextWidth() { 
     return getMeasuredWidth(); 
    } 

    /** 
    * Get max lines number. It parsed from XML attributes. Default value is 1. 
    */ 
    public int getMaxLines() { 
     return maxLines; 
    } 

    @Override 
    protected void onTextChanged(CharSequence text, int start, int before, 
      int after) { 
     super.onTextChanged(text, start, before, after); 
     requestLayout(); 
    } 

    /** 
    * Get initial text size. 
    */ 
    public float getInitialTextSize() { 
     return initialTextSize; 
    } 
} 

正如你可能猜到的那樣，在助手中沒有，也沒有曾經有過一個關於lightstreamer庫的單一引用，它只負責一些測量cust om意見。這使我認爲這是Dalvik VM中的一個錯誤。

順便說一句，該應用程序是像往常一樣在Eclipse中構建的。

是的，按鈕上的文字確實是而不是來自lightstreamer提供的值，我可以保證。

Answer 1

看在正確的文件/類:-)

唯一的例外來自於類ShrinkingTextViewHelper在com.ourapp.view而類貼住在com.ourapp。

快樂編碼。