Android：后台给button绑定onClick事件、当返回项目到手机页面时提示是否退出APP

上一篇文章我们学习了android通过findViewById的方式查找控件，本章将了解button控件，及btton如何绑定控件。

通过android的ui设计工具设计一个登录页面：

<RelativeLayout 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"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context=".MainActivity" >

    <TextView
        android:id="@+id/tvUsername"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_above="@+id/etPassword"
        android:layout_alignParentLeft="true"
        android:text="@string/main_activity_username" />

    <TextView
        android:id="@+id/tvPassword"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignBaseline="@+id/etPassword"
        android:layout_alignBottom="@+id/etPassword"
        android:layout_alignLeft="@+id/tvUsername"
        android:text="@string/main_activity_password" />

    <EditText
        android:id="@+id/etUsername"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentTop="true"
        android:layout_marginLeft="15dp"
        android:layout_marginTop="42dp"
        android:layout_toRightOf="@+id/tvUsername"
        android:hint="@string/main_activity_username_hint"
        android:ems="10" />

    <EditText
        android:id="@+id/etPassword"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignLeft="@+id/etUsername"
        android:layout_below="@+id/etUsername"
        android:layout_marginTop="41dp"
        android:hint="@string/main_activity_password_hint"
        android:ems="10"
        android:inputType="textPassword" >

        <requestFocus />
    </EditText>

    <Button
        android:id="@+id/btnCancel"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignBottom="@+id/btnOk"
        android:layout_alignRight="@+id/etUsername"
        android:layout_marginRight="57dp"
        android:text="@string/main_activity_btnCancel" />

    <Button
        android:id="@+id/btnOk"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@+id/etPassword"
        android:layout_marginRight="32dp"
        android:layout_marginTop="59dp"
        android:layout_toLeftOf="@+id/btnCancel"
        android:text="@string/main_activity_btnOk" />

    <TextView
        android:id="@+id/tvShow"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignLeft="@+id/tvPassword"
        android:layout_alignParentBottom="true"
        android:layout_alignRight="@+id/etUsername"
        android:layout_marginBottom="74dp"
        android:text="" />

</RelativeLayout>

1）文本框使用的EditText控件；

2）文本hint是输入提示；

3）inputType是文本内容的格式设定。

后台给button绑定onClick事件：

android后台绑定button的onClick的函数setOnClickListener函数：

package com.example.helloword;

import android.app.Activity;
import android.os.Bundle;
import android.view.Menu;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;

public class MainActivity extends Activity {
    private EditText etUsername, etPassword;
    private TextView tvUsername, tvPassword, tvShow;
    private Button btnOk, btnCancel;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        etUsername = (EditText) this.findViewById(R.id.etUsername);
        etPassword = (EditText) this.findViewById(R.id.etPassword);
        tvUsername = (TextView) this.findViewById(R.id.tvUsername);
        tvPassword = (TextView) this.findViewById(R.id.tvPassword);
        tvShow = (TextView) this.findViewById(R.id.tvShow);
        btnOk = (Button) this.findViewById(R.id.btnOk);
        btnCancel = (Button) this.findViewById(R.id.btnCancel);

        btnOk.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View arg0) {
                String username = etUsername.getText().toString();
                String password = etPassword.getText().toString();

                tvShow.setText(username + "," + password);
            }
        });
        btnCancel.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View arg0) {
                etUsername.setText("");
                etPassword.setText("");
                tvShow.setText("");
            }
        });
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }
}

当返回项目到手机页面时提示是否退出APP

    @Override
    public boolean onKeyUp(int keyCode, KeyEvent event) {
        // 当点击回退时，弹出该窗口（也就相当于关闭操作）
        if (keyCode == KeyEvent.KEYCODE_BACK) {
            new AlertDialog.Builder(this).setTitle("是否退出？")
                    .setPositiveButton("确定", new OnClickListener() {
                        @Override
                        public void onClick(DialogInterface arg0, int arg1) {
                            finish();
                        }
                    }).setNegativeButton("取消", null).show();
            return true;
        }
        return super.onKeyUp(keyCode, event);
    }

使用android仿真机测试效果：

当点击返回到手机时：