活动中有活动A和B.

Question

我有活动A和B.在活动A中，我加载数据然后当单击列表时它将我移动到活动B.当返回活动A时，数据再次加载。如何防止这种情况？

Answer 1

当您从一个活动移动到另一个活动时，例如从活动A移动到活动B，那么您加载的数据将丢失。要防止数据重新加载，您需要覆盖onSaveInstanceState（Bundle savedInstance）。

@Override
public void onSaveInstanceState(Bundle savedInstanceState) {
  super.onSaveInstanceState(savedInstanceState);
  // Save UI state changes to the savedInstanceState.
  // This bundle will be passed to onCreate if the process is
  // killed and restarted.
  savedInstanceState.putBoolean("MyBoolean", true);
  savedInstanceState.putDouble("myDouble", 1.9);
  savedInstanceState.putInt("MyInt", 1);
  savedInstanceState.putString("MyString", "Welcome back to Android");
  // etc.
}

您可以通过覆盖onRestoreInstanceState（Bundle savedInstance）来提取这些值。

@Override
public void onRestoreInstanceState(Bundle savedInstanceState) {
  super.onRestoreInstanceState(savedInstanceState);
  // Restore UI state from the savedInstanceState.
  // This bundle has also been passed to onCreate.
  boolean myBoolean = savedInstanceState.getBoolean("MyBoolean");
  double myDouble = savedInstanceState.getDouble("myDouble");
  int myInt = savedInstanceState.getInt("MyInt");
  String myString = savedInstanceState.getString("MyString");
}

您还可以存储和检索arraylist。