view，视图组件

<?xml version="1.0" encoding="utf-8"?><GridLayout xmlns:android="http://schemas.android.com/apk/res/android"    xmlns:tools="http://schemas.android.com/tools"    android:layout_width="match_parent"    android:layout_height="match_parent"    tools:context="com.hanqi.testapp3.MainActivity"    android:rowCount="5"    android:columnCount="4"    >

    <TextView        android:layout_width="match_parent"        android:layout_height="50dp"        android:layout_columnSpan="4"        android:id="@+id/tv_1"        android:text="7"        android:gravity="right|center_vertical"        android:textSize="30sp"        android:paddingRight="10dp"        android:textColor="#0f0"/>    <Button android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:gravity="center"        android:text="7"        />    <Button android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:gravity="center"        android:text="8"        />    <Button android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:gravity="center"        android:text="9"        android:id="@+id/bt9"/></GridLayout>

package com.hanqi.testapp3;

import android.support.v7.app.AppCompatActivity;import android.os.Bundle;import android.view.View;import android.widget.Button;import android.widget.TextView;

public class MainActivity extends AppCompatActivity {    TextView tv_1;    Button bt9;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        tv_1=(TextView)findViewById(R.id.tv_1);        //事件源        bt9=(Button)findViewById(R.id.bt9);        //给bt9按钮添加监听器 实现方式：1.匿名内部类        bt9.setOnClickListener(new View.OnClickListener() {            @Override            public void onClick(View v) {                //处理事件的业务逻辑                tv_1.setText("9");            }        });        //内部类

    }    public void bt7_OnClick(View v)    {        tv_1.setText("7");    }    public void bt8_OnClick(View v)    {        tv_1.setText("8");    }    public void bt9_OnClick(View v)    {        tv_1.setText("9");    }}