<?xml version="1.0" encoding="utf-8"?>

<LinearLayout

    xmlns:android="http://schemas.android.com/apk/res/android"

    xmlns:tools="http://schemas.android.com/tools"

    xmlns:app="http://schemas.android.com/apk/res-auto"

    android:layout_width="match_parent"

    android:layout_height="match_parent"

    android:orientation="vertical">

    <Button

        android:id="@+id/btn1"

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:text="Hello World!"

        android:layout_gravity="center"

        android:layout_marginTop="60pt"

        android:textAllCaps="false"

        />

    <Button

        android:id="@+id/btn2"

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:layout_gravity="center"

        android:text="Button"

        android:layout_marginTop="3pt"

        android:textAllCaps="false"

        />

</LinearLayout>

package com.example.administrator.myappalertdialog;

import android.app.ProgressDialog;

import android.content.DialogInterface;

import android.preference.DialogPreference;

import android.support.v7.app.ActionBar;

import android.support.v7.app.AlertDialog;

import android.support.v7.app.AppCompatActivity;

import android.os.Bundle;

import android.view.View;

import android.widget.Button;

import android.widget.Toast;

public class MainActivity extends AppCompatActivity implements View.OnClickListener {

    private Button mBtn1;

    private Button mBtn2;  //声明控件

    @Override

    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);

        ActionBar actionbar = getSupportActionBar();  // 去除标题栏

        if(actionbar!= null)

        {

            actionbar.hide();

        }

        mBtn1 = (Button) findViewById(R.id.btn1);  //查找控件

        mBtn1.setOnClickListener(this);   //创建点击事件

        mBtn2 = (Button) findViewById(R.id.btn2);

        mBtn2.setOnClickListener(this);

    }

    public void onClick(View view)  //点击事件

    {

        switch(view.getId())

        {

            case R.id.btn1:AlertDialog.Builder dialog = new AlertDialog.Builder(MainActivity.this);

                dialog.setTitle("This is AlertDialog");  //对话框标题

                dialog.setMessage("Hello world!");　　//内容

                dialog.setCancelable(true);　　　　//可撤销性

                dialog.setPositiveButton("OK", new DialogInterface.OnClickListener() {

                    @Override

                    public void onClick(DialogInterface dialog, int which) {

                        Toast.makeText(MainActivity.this,"OK",Toast.LENGTH_SHORT).show();  //提示内容

                    }   //确定按钮的点击事件

                });

                dialog.setNegativeButton("Cancel", new DialogInterface.OnClickListener() {

                    @Override

                    public void onClick(DialogInterface dialog, int which) {

                        Toast.makeText(MainActivity.this,"Cancel",Toast.LENGTH_SHORT).show();  //提示内容

                    }//取消按钮的点击事件

                });

                dialog.show();  //全部显示出来

                break;

//下面的原理一样。

            case R.id.btn2:

                ProgressDialog progressdialog = new ProgressDialog(MainActivity.this);

                progressdialog.setTitle("This is ProgressDialog");

                progressdialog .setMessage("Mr.Jiang");

                progressdialog.setCancelable(false);

                progressdialog.show();

                break;

            default: Toast.makeText(MainActivity.this,"ERROR",Toast.LENGTH_SHORT).show();break;

        }

    }

}