监听EditText的变化

http://liangruijun.blog.51cto.com/3061169/729505

之前博客上的有关EditText的文章，只是介绍EditText的一些最基本的用法，这次来深入学习一下EditText。

监听EditText的变化

使用EditText的addTextChangedListener(TextWatcher watcher)方法对EditText实现监听，TextWatcher是一个接口类，所以必须实现TextWatcher里的抽象方法：

 当EditText里面的内容有变化的时候，触发TextChangedListener事件，就会调用TextWatcher里面的抽象方法。

MainActivity.java

    package com.lingdududu.watcher;  
     
    import android.app.Activity;  
    import android.app.AlertDialog;  
    import android.content.DialogInterface;  
    import android.os.Bundle;  
    import android.text.Editable;  
    import android.text.TextWatcher;  
    import android.util.Log;  
    import android.widget.EditText;  
     
    public class MainActivity extends Activity {  
        private EditText text;  
        String str;  
        @Override 
        public void onCreate(Bundle savedInstanceState) {  
            super.onCreate(savedInstanceState);  
            setContentView(R.layout.main);  
              
            text = (EditText)findViewById(R.id.text);  
            text.addTextChangedListener(textWatcher);  
        }  
          
        private TextWatcher textWatcher = new TextWatcher() {  
              
            @Override    
            public void afterTextChanged(Editable s) {     
                // TODO Auto-generated method stub     
                Log.d("TAG","afterTextChanged--------------->");   
            }   
              
            @Override 
            public void beforeTextChanged(CharSequence s, int start, int count,  
                    int after) {  
                // TODO Auto-generated method stub  
                Log.d("TAG","beforeTextChanged--------------->");  
            }  
     
             @Override    
            public void onTextChanged(CharSequence s, int start, int before,     
                    int count) {     
                Log.d("TAG","onTextChanged--------------->");    
                str = text.getText().toString();  
                try {  
                    //if ((heighText.getText().toString())!=null)   
                    Integer.parseInt(str);  
                      
                } catch (Exception e) {  
                    // TODO: handle exception  
                    showDialog();  
                }  
                                  
            }                    
        };  
     
        private void showDialog(){  
            AlertDialog dialog;  
            AlertDialog.Builder builder = new AlertDialog.Builder(MainActivity.this);  
            builder.setTitle("消息").setIcon(android.R.drawable.stat_notify_error);  
            builder.setMessage("你输出的整型数字有误，请改正");  
            builder.setPositiveButton("确定", new DialogInterface.OnClickListener(){  
                @Override 
                public void onClick(DialogInterface dialog, int which) {  
                    // TODO Auto-generated method stub  
                      
                }                     
            });  
            dialog = builder.create();  
            dialog.show();  
        }  
    } 

 main.xml

    <?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:layout_width="fill_parent"   
        android:layout_height="wrap_content"   
        android:text="请输入整型数字" 
        /> 
    <EditText   
        android:id="@+id/text" 
        android:layout_width="fill_parent"   
        android:layout_height="wrap_content"   
        /> 
    </LinearLayout> 

 效果图：

当我们在输入框输入不是整型数字的时候，会立刻弹出输入框，提示你改正

在LogCat查看调用这些方法的顺序：

beforeTextChanged-->onTextChanged-->onTextChanged

第二个例子实现了提示文本框还能输入多少个字符的功能

    package com.lingdududu.test;  
     
    import android.app.Activity;  
    import android.os.Bundle;  
    import android.text.Editable;  
    import android.text.TextWatcher;  
    import android.view.View;  
    import android.widget.Button;  
    import android.widget.EditText;  
    import android.widget.TextView;  
     
    public class MainActivity extends Activity {  
     private Button clearBtn;  
     private EditText et;  
     private TextView tv;  
     final int MAX_LENGTH = 20;  
     int Rest_Length = MAX_LENGTH;  
        @Override 
        public void onCreate(Bundle savedInstanceState) {  
            super.onCreate(savedInstanceState);  
            setContentView(R.layout.main);  
            tv =(TextView)findViewById(R.id.tv);  
            et = (EditText)findViewById(R.id.et);  
              
            clearBtn = (Button)findViewById(R.id.btn);  
     
            et.addTextChangedListener(new TextWatcher() {  
                              
                @Override 
                public void beforeTextChanged(CharSequence s, int start, int count,  
                        int after) {  
                    tv.setText("还能输入"+Rest_Length+"个字");              
                }  
                              
                @Override 
                public void afterTextChanged(Editable s) {  
                    tv.setText("还能输入"+Rest_Length+"个字");  
                }  
                  
                @Override 
                public void onTextChanged(CharSequence s, int start, int before, int count) {  
                    if(Rest_Length>0){  
                        Rest_Length = MAX_LENGTH - et.getText().length();  
                    }  
                }             
            });  
            
            clearBtn.setOnClickListener(new Button.OnClickListener() {        
                @Override 
                public void onClick(View v) {  
                    et.setText("");  
                    Rest_Length = MAX_LENGTH;  
                }  
            });  
        }  
     } 

效果图：

本文出自 “IT的点点滴滴” 博客，请务必保留此出处http://liangruijun.blog.51cto.com/3061169/729505