为什么addAll清除ArrayList从中提取数据？

Question

我有一个片段发送一个ArrayList，newStyles到它的FragmentActivity，mStyles，然后使用addAll将其清零。我已经使用.size（）来检查数组，并注意source，newStyles在addAll被调用后被清除：

以下将在调用addAll之前给出newStyles的正确大小，但在它之后为0大小清除：

public void setStyles(ArrayList<String[][]> newStyles) { 
    Log.d(TAG, "setStyles: mStyles.size() = " + mStyles.size()); 
    Log.d(TAG, "setStyles: newStyles.size() = " + newStyles.size()); 

    mStyles.clear(); 
    mStyles.addAll(newStyles); 

    Log.d(TAG, "setStyles: mStyles.size() = " + mStyles.size()); 
    Log.d(TAG, "setStyles: newStyles.size() = " + newStyles.size()); 
} 

什么结束了发生的事情是双方的ArrayList最终通过使用具有尺寸为0

UPDATE

我解决了它：

mStyles = new ArrayList<String[][]>(newStyles); 

但我还是想知道发生了什么事情所以这里的必要信息

下面是活动中：

ArrayList<String[][]> mStyles; 

protected void onCreate(Bundle savedInstanceState) { 
... 
mStyles = new ArrayList<String[][]>(); 
.... 
} 

// Called by StylesFragment to preLoad styles from the file when 
// the Fragment is viewed 
public ArrayList<String[][]> getStylesFromFile() { 

    mStyles.clear(); 
    mStyles.addAll(mTotalsFragment.getStyles()); 

    return mStyles; 
} 

// Called by StylesFragment when changes are made to styles 
public void setStyles(ArrayList<String[][]> newStyles) { 
    Log.d(TAG, "setStyles: mStyles.size() = " + mStyles.size()); 
    Log.d(TAG, "setStyles: newStyles.size() = " + newStyles.size()); 

    mStyles.clear(); 
    mStyles.addAll(newStyles); 

    Log.d(TAG, "setStyles: mStyles.size() = " + mStyles.size()); 
    Log.d(TAG, "setStyles: newStyles.size() = " + newStyles.size()); 
} 

以下是汇总片段中：

ArrayList<String[][]> mStyles; 

public void onActivityCreated(Bundle savedInstanceState) { 
... 
mStyles = new ArrayList<String[][]>(); 
... 
} 

public void loadEstimate() { 
... 
// Do loop here to pull data from a file 
mStyle = ... 
... 
} 

// Called by StylesFragment via Activity 
// to get Loaded data from file 
public ArrayList<String[][]> getStyles() { 

    return mStyles; 
} 

public void saveEstimate() { 
... 
// Get the styles that should be in Activity 
mStyles = ((PagerActivityFragment)getActivity()).getStyles(); 

// Save the file with the new information 
... 
} 

以下是内StylesFragment：

ArrayList<String[][]> mStyles; 

public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { 
... 
mStyles = new ArrayList<String[][]>(); 
... 
} 

public void onResume() { 
... 
// Pull the styles loaded from the file through Activity 
mStyles = ((PagerActivityFragment)getActivity()).getStylesFromFile(); 
... 
} 

public modifyStyle(stylePos) { 
... 
// Do some stuff here to modify a specific style (String[][]) within the ArryaList 

// Now send changes back to Activity so TotalsFragment can pull it 
// even if this Fragment is not available when file is to be saved 
((PagerActivityFragment)getActivity()).setStyles(mStyles); 
} 

Answer 1

return mStyles in getStylesFromFile() in Activity is returned the reference to the list mStyles这就是为什么两个指向相同的List。