今天看downloadmanager源码发现 cursorAdapter 会在数据变化的情况下没有调用notifydatasetxx() 而是自动刷新。和其他adapeter刷新方式不一样。
看了一下源码,发现cursoradapter内部有自动的刷新代码。如下:
void init(Context context, Cursor c, int flags) { if ((flags & FLAG_AUTO_REQUERY) == FLAG_AUTO_REQUERY) { flags |= FLAG_REGISTER_CONTENT_OBSERVER; mAutoRequery = true; } else { mAutoRequery = false; } boolean cursorPresent = c != null; mCursor = c; mDataValid = cursorPresent; mContext = context; mRowIDColumn = cursorPresent ? c.getColumnIndexOrThrow("_id") : -1; if ((flags & FLAG_REGISTER_CONTENT_OBSERVER) == FLAG_REGISTER_CONTENT_OBSERVER) { mChangeObserver = new ChangeObserver(); mDataSetObserver = new MyDataSetObserver(); } else { mChangeObserver = null; mDataSetObserver = null; } if (cursorPresent) { if (mChangeObserver != null) c.registerContentObserver(mChangeObserver); if (mDataSetObserver != null) c.registerDataSetObserver(mDataSetObserver); } }
observer代码中会进行数据更新,如下:
private class MyDataSetObserver extends DataSetObserver { @Override public void onChanged() { mDataValid = true; notifyDataSetChanged(); } @Override public void onInvalidated() { mDataValid = false; notifyDataSetInvalidated(); } }