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