Google official notes and google notes

Google official notes and google notes

In addition to the popular xutils butterknife annotation framework, google has begun to add its own annotation to support package 19.1, an internal beta version.

Use gradle to add this sentence to your project:

compile 'com.android.support:support-annotations:20.0.0'

Let's take a look at three basic types:

• Nullness
• Resource type
• IntDef and StringDef

Next, let's take a look at how they use Nullness.

@NonNullParameter cannot be blank

This Code uses this annotation to pass a null parameter in the past:

public class MainActivity extends ActionBarActivity {    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        String name = null;        sayHello(name);    }    void sayHello(@NonNull String s) {        Toast.makeText(this, "Hello " + s, Toast.LENGTH_LONG).show();    }}

IDE sends a warning

The warning of using non-null parameters disappears.

@NullableThe parameter or return value cannot be blank.

public class MainActivity extends ActionBarActivity {    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        User user = new User("Our Lord Duarte");        Toast.makeText(this, "Hello " + getName(user), Toast.LENGTH_LONG).show();    }    @Nullable    String getName(@NonNull User user) {        return user.getName();    }}

Used@ NullableAnnotation opportunity helps us check

Toast.makeText(this, "Hello " + getName(user), Toast.LENGTH_LONG).show();

If you do not check whether it is null, there will be potential crash problems.

For more details, refer:

Http://anupcowkur.com/posts/a-look-at-android-support-annotations/