TextWatcher的简单使用

xml文件

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/activity_main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context="com.example.administrator.helloword.MainActivity">
    <EditText
        android:id="@+id/editText"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:inputType="text"/>
    <TextView
        android:text="TextView"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:textColor="#000000"
        android:id="@+id/textView"
        android:gravity="center"/>
</LinearLayout>

MainActivity源码

package com.example.administrator.helloword;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.text.Editable;
import android.text.TextWatcher;
import android.widget.EditText;
import android.widget.TextView;

public class MainActivity extends AppCompatActivity {

    private EditText ed;
    private TextView showResult_tv;
    private String getResult;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        ed = (EditText)findViewById(R.id.editText);
        showResult_tv = (TextView)findViewById(R.id.textView);
        showResult_tv.setHint("没有内容");
        //设置文本改变监听
        ed.addTextChangedListener(tw);
    }
    //文本改变监听器
    TextWatcher tw = new TextWatcher() {
        //文字改变前的监听
        @Override
        public void beforeTextChanged(CharSequence charSequence, int i, int i1, int i2) {
        }
        //文本改变时的监听
        @Override
        public void onTextChanged(CharSequence charSequence, int i, int i1, int i2) {
            if (ed.getText().toString() == null || ed.getText().toString() == "") {
                showResult_tv.setText("");
            } else {
                showResult_tv.setText(ed.getText().toString());
            }
        }
        //文字改变后的监听
        @Override
        public void afterTextChanged(Editable editable) {
        }
    };
}