(1) Android uses custom annotations to initialize controls. android Initialization

(1) Android uses custom annotations to initialize controls. android Initialization

Generally, we develop Android applications and use findViewById () to initialize controls. However, after a project is developed, you will find a lot of such code, which is actually repeated. At this time, you will find out how convenient the built-in Annotation (Annotation) in Java is.

1. Design a comment for ContentView

Because this annotation will be carried on the Activity class, we need to declare @ Targrt (ElementType. TYPE ).

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1. @ Target (ElementType. TYPE)
2. @ Retention (RetentionPolicy. RUNTIME)
4. Public @ interface ContentView {
5. Value ();
6. }

2. Design a comment for ContentWidget

Because this annotation is carried to the member variables of the class, we need to declare @ Targrt (ElementType. FILELD ). Class member variables specify the control objects we declare

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1. @ Target (ElementType. FIELD)
2. @ Retention (RetentionPolicy. RUNTIME)
3. Public @ interface ContentWidget {
4. Int value ();
5. }

3. Design a tool class to extract and process the information of the aforementioned custom Annotation class

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1. Public static void injectObject (Object object, Activity activity ){
3. Class <?> ClassType = object. getClass ();
5. // Whether the class has a ContentView Annotation
6. If (classType. isAnnotationPresent (ContentView. class )){
7. // Return the existing ContentView Annotation
8. ContentView annotation = classType. getAnnotation (ContentView. class );
11. Try {
14. // Return a Method object that reflects the specified public member methods of the classes or interfaces represented by this Class object.
15. Method method = classType
16. . GetMethod ("setContentView", int. class );
17. Method. setAccessible (true );
18. Int resId = annotation. value ();
19. Method. invoke (object, resId );
22. } Catch (NoSuchMethodException e ){
23. // TODO Auto-generated catch block
24. E. printStackTrace ();
25. } Catch (IllegalArgumentException e ){
26. // TODO Auto-generated catch block
27. E. printStackTrace ();
28. } Catch (IllegalAccessException e ){
29. // TODO Auto-generated catch block
30. E. printStackTrace ();
31. } Catch (InvocationTargetException e ){
32. // TODO Auto-generated catch block
33. E. printStackTrace ();
34. }
37. }
40. // Returns an array of the Field object. These objects reflect the member variables declared by the Class object or interface,
41. // Includes public, protected, default (Package) Access, and private member variables, but does not include inherited member variables.
42. Field [] fields = classType. getDeclaredFields ();
45. If (null! = Fields & fields. length> 0 ){
48. For (Field field: fields ){
49. // Whether the member variable has a ContentWidget Annotation
50. If (field. isAnnotationPresent (ContentWidget. class )){
53. ContentWidget annotation = field
54. . GetAnnotation (ContentWidget. class );
55. Int viewId = annotation. value ();
56. View view = activity. findViewById (viewId );
57. If (null! = View ){
58. Try {
59. Field. setAccessible (true );
60. Field. set (object, view );
61. } Catch (IllegalArgumentException e ){
62. // TODO Auto-generated catch block
63. E. printStackTrace ();
64. } Catch (IllegalAccessException e ){
65. // TODO Auto-generated catch block
66. E. printStackTrace ();
67. }
68. }
71. }
74. }
77. }
80. }

4. How should we use the annotation defined in the Activity class?

[Java]View plaincopyprint?

1. @ ContentView (R. layout. activity_main)
2. Public class MainActivity extends Activity {
4. @ ContentWidget (R. id. TV)
5. Private TextView textView;
7. @ Override
8. Protected void onCreate (Bundle savedInstanceState ){
9. Super. onCreate (savedInstanceState );
10. // SetContentView (R. layout. activity_main );
11. ViewUtils. injectObject (this, this );
13. TextView. setText ("Custom comment ");
14. }

 

Although there are a lot of preparations in the early stage, it will save a lot of trouble for loading layout and initializing controls during the development process in the back sequence. This is especially important for large projects, click it to cut the worker without mistake!

DEMO address

How do android custom controls input values during initialization?

If you use code, just pass the value to the constructor.
Configure and add attributes by yourself in xml, and assign values to attributes


Android control array definition and usage Problems

Bv = new Button [10];
You just created an array to store 10 buttons.
However, you have not initialized the Button.
Bv [I] = null; changed to bv [I] = new Button (this );