Question

我有一个Fragment将一个ArrayList，newStyles发送到它的FragmentActivity，mStyles，然后使用addAll将其清除。我使用.size（）来检查数组并注意在调用addAll后清除源newStyles：

以下将在调用addAll之前为newStyles提供正确的大小，但在清除之后将为0大小：

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());
}

最终发生的事情是ArrayLists最终的大小为0。

更新

我通过使用：

解决了它

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

但我仍然想知道发生了什么，所以这里是必要的信息

以下是在活动中：

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Totals Fragment：

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
...
}

以下是在StylesFragment中：

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中的getStylesFromFile()中的Activity正在返回对mStyles列表的引用，这就是为什么两者都指向相同的列表。

为什么addAll清除ArrayList从中提取数据？

1 个答案: