android源代码提示文本框还能输入多少个字符

publicclassTestAndroidActivityextendsActivity{
/**Calledwhentheactivityisfirstcreated.*/

Buttonclearbtn;
EditTextet;
TextViewtv;
finalintMAX_LENGTH=50;
intRest_Length=MAX_LENGTH;

@Override
publicvoidonCreate(BundlesavedInstanceState){
super.onCreate(savedInstanceState);
setContentView(R.layout.main);

//tv=(TextView)findViewById(R.);
tv=(TextView)this.findViewById(R.id.btn);
//tv=this.findViewById(R.)
et=(EditText)this.findViewById(R.id.bg);

et.addTextChangedListener(newTextWatcher(){

publicvoidonTextChanged(CharSequences,intstart,intbefore,intcount){
if(Rest_Length>0){
Rest_Length=MAX_LENGTH-et.getText().length();
}
}

publicvoidbeforeTextChanged(CharSequences,intstart,intcount,
intafter){
tv.setText("还可以输入"+Rest_Length+"个字");

}

publicvoidafterTextChanged(Editables){
tv.setText("还可以输入"+Rest_Length+"个字");
}
});

clearbtn=(Button)findViewById(R.id.btn);
clearbtn.setOnClickListener(newButton.OnClickListener(){

publicvoidonClick(Viewv){
et.setText("");
Rest_Length=MAX_LENGTH;
}
});
}
}