java - 在获取 NPE 的 Activity 中调用 Fragment 方法

Question

这个问题已经有答案了:

What is a NullPointerException, and how do I fix it? (12 个回答)

已关闭 6 年前。

我想调用MainFragment.java的方法来自MainActivity.java

这是我尝试过的:

MainActivity.java

MainFragment mainFragment;

........

mainFragment = new MainFragment();

.........

mainFragment.deom();

MainFragment.java

public void deom() {

    Toast.makeText(getActivity(), "Demo", Toast.LENGTH_LONG).show();

}

日志

java.lang.NullPointerException
at android.widget.Toast.<init>(Toast.java:93)
at android.widget.Toast.makeText(Toast.java:241)
at com.example.x.b(Unknown Source)
at com.example.MainActivity.onOptionsItemSelected(Unknown Source)
at android.app.Activity.onMenuItemSelected(Activity.java:2633)
at android.support.v4.b.ao.onMenuItemSelected(Unknown Source)
at android.support.v7.app.t.onMenuItemSelected(Unknown Source)
at android.support.v7.view.n.onMenuItemSelected(Unknown Source)
at android.support.v7.view.n.onMenuItemSelected(Unknown Source)

我可以知道我哪里做错了吗？我错过了什么？为什么我会得到 NPE。

Answer 1

您必须初始化 MainFargment。

MainFragment mainFragment = (MainFragment) getFragmentManager.findFragmentById(R.id.theId);

mainFragment.deom();