Question

public AsyncSyncWithCloud(HistoryFragmentActivity historyFragmentActivity) {
    this.historyFragmentActivity = historyFragmentActivity;
    progressDialog = new ProgressDialog(historyFragmentActivity);

    // ???
    // java.lang.ClassCastException: android.view.ContextThemeWrapper cannot be cast to xxx.charting.HistoryFragmentActivity
    HistoryFragmentActivity test = ((HistoryFragmentActivity)progressDialog.getContext());
}

我很想知道，为什么我将自己的Activity作为上下文传递给ProgressDialog。当我从progressDialog执行getContext时，我没有得到我之前传递的内容？

Answer 1

不确定这是不错的解决方案

    private HistoryFragmentActivity getHistoryFragmentActivity(ProgressDialog progressDialog) {
        return (HistoryFragmentActivity)(((android.content.ContextWrapper)progressDialog.getContext()).getBaseContext());
    }

Answer 2

正如您所发现的那样，背景已被包裹。

如果向下钻取，您将在构造函数中找到： -

    Dialog(Context context, int theme, boolean createContextThemeWrapper) {
    if (createContextThemeWrapper) {
        if (theme == 0) {
            TypedValue outValue = new TypedValue();
            context.getTheme().resolveAttribute(com.android.internal.R.attr.dialogTheme,
                    outValue, true);
            theme = outValue.resourceId;
        }
        mContext = new ContextThemeWrapper(context, theme);
    } else {
        mContext = context;
    }

    mWindowManager = (WindowManager)context.getSystemService(Context.WINDOW_SERVICE);
    Window w = PolicyManager.makeNewWindow(mContext);
    mWindow = w;
    w.setCallback(this);
    w.setOnWindowDismissedCallback(this);
    w.setWindowManager(mWindowManager, null, null);
    w.setGravity(Gravity.CENTER);
    mListenersHandler = new ListenersHandler(this);
}

当当前没有设置主题时包装上下文。

虽然你可以按照你的方式进行投射，但我不确定它有多可靠 - 你可以在它周围放置instanceof检查，但可能你需要查看整个从新的角度来看。

通常，从片段中获取活动的最佳方法是使用getActivity（）并转换它。更好的是在onAttach（）方法上附加一个监听器：

Override
public void onAttach(Activity activity) {
    super.onAttach(activity);
    try {
        listener = (Listener) activity;
    } catch (ClassCastException e) {
        throw new ClassCastException(TAG
                + " must implement Listener");
    }
}

@Override
public void onDetach() {
    listener = null;
    super.onDetach();
}

ProgressDialog的getContext不是我传入的内容

2 个答案: