【Android进阶学习】监听EditText的变化

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：