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

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

    android:layout_width="match_parent"

    android:layout_height="match_parent"

    android:orientation="vertical">

   <TextView

       android:id="@+id/tv"

       android:layout_width="match_parent"

       android:layout_height="wrap_content"

       android:gravity="center"

       android:text="单选对话框"

       android:layout_marginTop="10dp"

       android:textSize="20sp"

       android:textColor="#fffdb371"/>

    <Button

        android:id="@+id/bt"

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:text="设置字体大小"

        android:layout_marginTop="20dp"

        android:layout_gravity="center"/>

</LinearLayout>

package com.iang.dialongdemo;

import android.content.DialogInterface;

import android.support.v7.app.AlertDialog;

import android.support.v7.app.AppCompatActivity;

import android.os.Bundle;

import android.view.View;

import android.widget.TextView;

public class MainActivity extends AppCompatActivity implements View.OnClickListener {

    private TextView textView;

    private int[] textSizeArr={10,20,25,30,40};

    int textSize=1;

//    加载资源文件，找到资源文件中的按钮id号

    @Override

    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.linear);

        findViewById(R.id.bt).setOnClickListener(this);

        textView=(TextView) findViewById(R.id.tv);

    }

    @Override

    public void onClick(View v) {

        AlertDialog dialog;

        AlertDialog.Builder builder=new AlertDialog.Builder(this)

                .setTitle("设置字体大小")

                .setIcon(R.mipmap.ic_launcher)

                .setSingleChoiceItems(new String[]{"小号", "默认", "中号", "大号", "超大"}, textSize, new DialogInterface.OnClickListener() {

                    @Override

                    public void onClick(DialogInterface dialog, int which) {

                        textSize=which;

                    }

                })

                .setPositiveButton("确定", new DialogInterface.OnClickListener() {

                    @Override

                    public void onClick(DialogInterface dialog, int which) {

                        textView.setTextSize(textSizeArr[textSize]);

                        dialog.dismiss();

                    }

                })

                .setNegativeButton("取消", new DialogInterface.OnClickListener() {

                    @Override

                    public void onClick(DialogInterface dialog, int which) {

                        dialog.dismiss();

                    }

                });

        dialog = builder.create();

        dialog.show();

    }

//   回退程序的使用

    @Override

    public void onBackPressed() {

       // super.onBackPressed();

        AlertDialog dialog;

        AlertDialog.Builder builder =new AlertDialog.Builder(this)

                .setTitle("普通对话框")    //设置对话框的标题

                .setIcon(R.mipmap.ic_launcher)   //设置标题图标

                .setMessage("是否确定退出应用:")

                .setPositiveButton("确定", new DialogInterface.OnClickListener() {

                    @Override

                    public void onClick(DialogInterface dialog, int which) {

                        dialog.dismiss();

                        MainActivity.this.finish();

                    }

                })

                .setNegativeButton("取消", new DialogInterface.OnClickListener() {

                    @Override

                    public void onClick(DialogInterface dialog, int which) {

                        dialog.dismiss();

                    }

                });

        dialog = builder.create();

        dialog.show();

    }

}