Button.setOnClickListener(OnClickListener l) 原理

android,java使用Button 可能都会监听之 当其被点击 就会有函数负责回调 那么其到底是怎么实现的呢？

今天要做的就是摸清楚之 为了减少不必要的麻烦 打算extends EditText 并在其上设立监听器

[代码 步骤]

1. 定义Edit2Text 且extends EditText

1. public class Edit2Text extends EditText {
   

2. OnTextChangedListener changedListener;
   

3. 
   

4. TextWatcher tWatcher;
   

5. }
   

6. 
   

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2. 定义其上的监听器：OnTextChangedListener 并定义函数：onChanged() 用于执行具体回调

1. public static interface OnTextChangedListener {
   

2. public void onChanged(Edit2Text e2t, String text);
   

3. 
   

4. }
   

5. 
   

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1. 需要注意的 这几行代码的修饰关键字：
   

2. 
   

3. 1. static ：使其能够脱离Edit2Text而存在
   

4. 
   

5. 2. interface : 使其自动填充其内部函数
   

6. 
   

7. 3. "void onChanged(Edit2Text e2t, String text)" 中的第一个参数e2t 用于做分别 具体奥妙 后面再细说
   

8. 
   

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1. public void setOnChangedListener(OnTextChangedListener l){
   

2. changedListener = l;
   

3. }
   

4. 
   

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4. 定义TextWatcher 当字符内容改变 通知监听器

* 定义TextWatcher'

1. tWatcher = new TextWatcher(){
   

2. @Override
   

3. public void afterTextChanged(Editable s) {
   

4. // TODO Auto-generated method stub
   

5. 06.
   

6. }
   

7. 
   

8. @Override
   

9. public void beforeTextChanged(CharSequence s, int start, int count,
   

10. int after) {
    

11. // TODO Auto-generated method stub
    

12. 
    

13. }
    

14. 
    

15. @Override
    

16. public void onTextChanged(CharSequence s, int start, int before,
    

17. int count) {
    

18. // TODO Auto-generated method stub
    

19. updateText(s.toString());
    

20. }
    

21. 
    

22. };
    

23. 
    

24. this.addTextChangedListener(tWatcher);
    

25. 
    

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1. private void updateText(String s){
   

2. changedListener.onChanged(this, s);
   

3. }
   

4. 
   

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1. public class Edit2TextTest extends Activity {
   

2. /** Called when the activity is first created. */
   

3. @Override
   

4. public void onCreate(Bundle savedInstanceState) {
   

5. super.onCreate(savedInstanceState);
   

6. 06. setContentView(R.layout.main);
   

7. Edit2Text e2t = new Edit2Text(this);
   

8. setContentView(e2t);
   

9. 
   

10. e2t.setOnChangedListener(new Edit2Text.OnTextChangedListener(){
    

11. @Override
    

12. public void onChanged(Edit2Text e2t, String text) {
    

13. // TODO Auto-generated method stub
    

14. Log.d("TAG","[String:]"+text);
    

15. }
    

16. });
    

17. }
    

18. }
    

19. 
    

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1. 
   

2. Java代码 收藏代码
   

3. 01. D/dalvikvm( 674): GC freed 223 objects / 8848 bytes in 108m
   

4. 02. D/TAG ( 941): [String:]i am
   

5. 03. D/TAG ( 941): [String:]i am
   

6. 04. D/TAG ( 941): [String:]i am e
   

7. 05. D/TAG ( 941): [String:]i am ed
   

8. 06. D/TAG ( 941): [String:]i am edi
   

9. 07. D/TAG ( 941): [String:]i am edit
   

10. 08. D/TAG ( 941): [String:]i am edit2
    

11. 09. D/TAG ( 941): [String:]i am edit2t
    

12. 10. D/TAG ( 941): [String:]i am edit2te
    

13. 11. D/TAG ( 941): [String:]i am edit2tex
    

14. 12. D/TAG ( 941): [String:]i am edit2text
    

15. 13. D/TAG ( 941): [String:]i am edit2text,
    

16. 14. D/TAG ( 941): [String:]i am edit2text,
    

17. 15. D/TAG ( 941): [String:]i am edit2text, h
    

18. 16. D/TAG ( 941): [String:]i am edit2text, he
    

19. 17. D/TAG ( 941): [String:]i am edit2text, hel
    

20. 18. D/TAG ( 941): [String:]i am edit2text, hell
    

21. 19. D/TAG ( 941): [String:]i am edit2text, hello
    

22. 20. D/TAG ( 941): [String:]i am edit2text, hello!