Android TextWatcher监控EditText中的输入内容并限制其输入字符个数

      布局中EditText在android布局中经常用到，对EditText中输入的内容也经常需要进行限制，我们可以通过TextWatcher去观察输入框中输入的内容，作个笔记。

主布局：

   
   
   
   

    
    
    
    <?
    
    
    
    xml version="1.0" encoding="utf-8"
    
    
    
    ?>
    
    
    
     
    
    
    
    <
    
    
    
    LinearLayout 
    
    
    
    xmlns:android
    
    
    
    ="http://schemas.android.com/apk/res/android"
    
    
    
     android:orientation
    
    
    
    ="vertical"
    
    
    
     android:layout_width
    
    
    
    ="fill_parent"
    
    
    
     android:layout_height
    
    
    
    ="fill_parent"
    
    
    
     
    
    
    
    >
    
    
    
     
    
    
    
    <
    
    
    
    TextView 
    
    
    
    android:id
    
    
    
    ="@+id/tv"
    
    
    
     android:layout_width
    
    
    
    ="fill_parent"
    
    
    
     android:layout_height
    
    
    
    ="wrap_content"
    
    
    
     android:textColor
    
    
    
    ="@android:color/white"
    
    
    
     android:ellipsize
    
    
    
    ="marquee"
    
    
    
     android:focusable
    
    
    
    ="true"
    
    
    
     android:marqueeRepeatLimit
    
    
    
    ="marquee_forever"
    
    
    
     android:focusableInTouchMode
    
    
    
    ="true"
    
    
    
     android:scrollHorizontally
    
    
    
    ="true"
    
    
    
     android:text
    
    
    
    ="Please input the text:"
    
    
    
     
    
    
    
    />
    
    
    
     
    
    
    
    <
    
    
    
    EditText 
    
    
    
    android:id
    
    
    
    ="@+id/ET"
    
    
    
     android:layout_width
    
    
    
    ="match_parent"
    
    
    
     android:layout_height
    
    
    
    ="wrap_content"
    
    
    
     android:inputType
    
    
    
    ="number"
    
    
    
    />
    
    
    
     
    
    
    
    </
    
    
    
    LinearLayout
    
    
    
    >
   
   
   
   

java代码：

  
  
  
  

   
   
   
   package
   
   
   
    com.android.text; 
   
   
   
   import
   
   
   
    android.app.Activity; 
   
   
   
   import
   
   
   
    android.os.Bundle; 
   
   
   
   import
   
   
   
    android.text.Editable; 
   
   
   
   import
   
   
   
    android.text.TextWatcher; 
   
   
   
   import
   
   
   
    android.util.Log; 
   
   
   
   import
   
   
   
    android.widget.EditText; 
   
   
   
   import
   
   
   
    android.widget.TextView; 
   
   
   
   import
   
   
   
    android.widget.Toast; 
   
   
   
   public
   
   
   
    
   
   
   
   class
   
   
   
    TextWatcherDemo 
   
   
   
   extends
   
   
   
    Activity { 
   
   
   
   private
   
   
   
    TextView mTextView; 
   
   
   
   private
   
   
   
    EditText mEditText; 
   
   
   
   /**
   
   
   
    Called when the activity is first created. 
   
   
   
   */
   
   
   
    @Override 
   
   
   
   public
   
   
   
    
   
   
   
   void
   
   
   
    onCreate(Bundle savedInstanceState) { 
   
   
   
   super
   
   
   
   .onCreate(savedInstanceState); setContentView(R.layout.main); mTextView 
   
   
   
   =
   
   
   
    (TextView)findViewById(R.id.tv); mEditText 
   
   
   
   =
   
   
   
    (EditText)findViewById(R.id.ET); mEditText.addTextChangedListener(mTextWatcher); } TextWatcher mTextWatcher 
   
   
   
   =
   
   
   
    
   
   
   
   new
   
   
   
    TextWatcher() { 
   
   
   
   private
   
   
   
    CharSequence temp; 
   
   
   
   private
   
   
   
    
   
   
   
   int
   
   
   
    editStart ; 
   
   
   
   private
   
   
   
    
   
   
   
   int
   
   
   
    editEnd ; @Override 
   
   
   
   public
   
   
   
    
   
   
   
   void
   
   
   
    beforeTextChanged(CharSequence s, 
   
   
   
   int
   
   
   
    arg1, 
   
   
   
   int
   
   
   
    arg2, 
   
   
   
   int
   
   
   
    arg3) { temp 
   
   
   
   =
   
   
   
    s; } @Override 
   
   
   
   public
   
   
   
    
   
   
   
   void
   
   
   
    onTextChanged(CharSequence s, 
   
   
   
   int
   
   
   
    arg1, 
   
   
   
   int
   
   
   
    arg2, 
   
   
   
   int
   
   
   
    arg3) { mTextView.setText(s); } @Override 
   
   
   
   public
   
   
   
    
   
   
   
   void
   
   
   
    afterTextChanged(Editable s) { editStart 
   
   
   
   =
   
   
   
    mEditText.getSelectionStart(); editEnd 
   
   
   
   =
   
   
   
    mEditText.getSelectionEnd(); 
   
   
   
   if
   
   
   
    (temp.length() 
   
   
   
   >
   
   
   
    
   
   
   
   10
   
   
   
   ) { Toast.makeText(TextWatcherDemo.
   
   
   
   this
   
   
   
   , 
   
   
   
   "
   
   
   
   你输入的字数已经超过了限制！
   
   
   
   "
   
   
   
   , Toast.LENGTH_SHORT) .show(); s.delete(editStart
   
   
   
   -
   
   
   
   1
   
   
   
   , editEnd); 
   
   
   
   int
   
   
   
    tempSelection 
   
   
   
   =
   
   
   
    editStart; mEditText.setText(s); mEditText.setSelection(tempSelection); } } }; }