Android中Fragment的构造函数 his fragment should provide a default constructor

16lz 2021-01-26

原文地址：http://blog.csdn.net/anobodykey/article/details/22503413

最近在使用Fragment的过程中遇到一个问题，初步是想在Fragment中创建一个构造函数，构造函数中传递两个自身需要的变量，如下

[java] view plain copy

public class TestFragment extends Fragment
{
private String name;
private String passwd;
public TestFragment(String name, String passwd)
{
super();
this.name = name;
this.passwd = passwd;
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// TODO Auto-generated method stub
View view = inflater.inflate(R.layout.main, null);
return view;
}
}

结果eclipse报出两个错：

This fragment should provide a default constructor (a public constructor with no arguments) (com.example.TestFragment)

Avoid non-default constructors in fragments: use a default constructor plus Fragment#setArguments(Bundle) instead

在增加一个空参数的构造函数可以消去第一个错误，但是第二个却不能，第二个错误说要使用默认构造函数外加setArguments(Bundle)来代替，去Android的官网上查看Fragment的例子都是下面这个样子的

[java] view plain copy

CharSequence mLabel;
/**
* Create a new instance of MyFragment that will be initialized
* with the given arguments.
*/
static MyFragment newInstance(CharSequence label) {
MyFragment f = new MyFragment();
Bundle b = new Bundle();
b.putCharSequence("label", label);
f.setArguments(b);
return f;
}

既然人家这么写例子肯定还是有道理的，我们只需要依葫芦画瓢就可以了，去掉带参的构造函数，创建一个newInstance函数，如下

[java] view plain copy

public class TestFragment extends Fragment
{
private String name;
private String passwd;
public static TestFragment newInstance(String name, string passwd) {
TestFragment newFragment = new TestFragment();
Bundle bundle = new Bundle();
bundle.putString("name", name);
bundle.putString("passwd", passwd);
newFragment.setArguments(bundle);
return newFragment;
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// TODO Auto-generated method stub
View view = inflater.inflate(R.layout.main, null);
return view;
}
}

如此这般，第二个错误就消失了，在Fragment所依赖的Activity中，用以下语句创建Fragment实例即可

[java] view plain copy

Fragment testFragment=TestFragment.newInstance("name","passwd");

对于从Activity传递到Fragment中的参数我们只需要在Fragment的onCreate中获取就可以了

[java] view plain copy

public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
Bundle args = getArguments();
if (args != null) {
name = args.getString("name");
passwd = args.getstring("passwd");
}
}

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