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
public class Edit2Text extends EditText {
OnTextChangedListener changedListener;
TextWatcher tWatcher;
}
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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
public static interface OnTextChangedListener {
public void onChanged(Edit2Text e2t, String text);
}
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需要注意的 这几行代码的修饰关键字：
- static ：使其能够脱离Edit2Text而存在
- interface : 使其自动填充其内部函数
- “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
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- 设定监听器
public void setOnChangedListener(OnTextChangedListener l){
changedListener = l;
}
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4. 定义TextWatcher 当字符内容改变 通知监听器
* 定义TextWatcher'
tWatcher = new TextWatcher(){
@Override <br style="word-wrap:break-word">
public void afterTextChanged(Editable s) { <br style="word-wrap:break-word">
// TODO Auto-generated method stub <br style="word-wrap:break-word">-
} <br style="word-wrap:break-word">
@Override <br style="word-wrap:break-word">
public void beforeTextChanged(CharSequence s, int start, int count, <br style="word-wrap:break-word">
int after) { <br style="word-wrap:break-word">
// TODO Auto-generated method stub <br style="word-wrap:break-word">
<br style="word-wrap:break-word">
} <br style="word-wrap:break-word"> @Override <br style="word-wrap:break-word">
public void onTextChanged(CharSequence s, int start, int before, <br style="word-wrap:break-word">
int count) { <br style="word-wrap:break-word">
// TODO Auto-generated method stub <br style="word-wrap:break-word">
updateText(s.toString()); <br style="word-wrap:break-word">
} <br style="word-wrap:break-word">
<br style="word-wrap:break-word">
}; <br style="word-wrap:break-word">
<br style="word-wrap:break-word">this.addTextChangedListener(tWatcher);
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- 通知监听器
private void updateText(String s){
changedListener.onChanged(this, s);
}
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- 如何使用
public class Edit2TextTest extends Activity {
/** Called when the activity is first created. */ <br style="word-wrap:break-word">@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState); <br style="word-wrap:break-word">-
setContentView(R.layout.main);
Edit2Text e2t = new Edit2Text(this);
setContentView(e2t); <br style="word-wrap:break-word"> <br style="word-wrap:break-word"> e2t.setOnChangedListener(new Edit2Text.OnTextChangedListener(){ <br style="word-wrap:break-word"> @Override <br style="word-wrap:break-word"> public void onChanged(Edit2Text e2t, String text) { <br style="word-wrap:break-word"> // TODO Auto-generated method stub <br style="word-wrap:break-word"> Log.d("TAG","[String:]"+text); <br style="word-wrap:break-word"> } <br style="word-wrap:break-word">
});
} <br style="word-wrap:break-word">}
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- Log 信息：
Java代码 收藏代码
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D/dalvikvm( 674): GC freed 223 objects / 8848 bytes in 108m
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D/TAG ( 941): [String:]i am
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D/TAG ( 941): [String:]i am
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D/TAG ( 941): [String:]i am e
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D/TAG ( 941): [String:]i am ed
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D/TAG ( 941): [String:]i am edi
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D/TAG ( 941): [String:]i am edit
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D/TAG ( 941): [String:]i am edit2
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D/TAG ( 941): [String:]i am edit2t
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D/TAG ( 941): [String:]i am edit2te
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D/TAG ( 941): [String:]i am edit2tex
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D/TAG ( 941): [String:]i am edit2text
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D/TAG ( 941): [String:]i am edit2text,
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D/TAG ( 941): [String:]i am edit2text,
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D/TAG ( 941): [String:]i am edit2text, h
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D/TAG ( 941): [String:]i am edit2text, he
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D/TAG ( 941): [String:]i am edit2text, hel
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D/TAG ( 941): [String:]i am edit2text, hell
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D/TAG ( 941): [String:]i am edit2text, hello
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D/TAG ( 941): [String:]i am edit2text, hello!