第五次作业

package com.example.myapplication112;


        import android.support.v7.app.ActionBarActivity;
        import android.app.AlertDialog;
        import android.content.DialogInterface;
        import android.graphics.Color;
        import android.os.Bundle;
        import android.view.Menu;
        import android.view.MenuItem;
        import android.view.View;
        import android.widget.RelativeLayout;

public class MainActivity extends ActionBarActivity {
    public int i = 0, r = 0, g = 0, b = 0;
    public int[] arr = { Color.rgb(0, 0, 255), Color.rgb(255, 0, 0),
            Color.rgb(255, 255, 255), Color.rgb(0, 0, 0), Color.rgb(0, 255, 0) };

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

    public void click(View v) {
        AlertDialog dialog;
        AlertDialog.Builder builder = new AlertDialog.Builder(this)
                .setTitle("设置字体大小")
                .setIcon(R.drawable.ic_launcher)
                .setSingleChoiceItems(
                        new String[] { "蓝色", "红色", "白色", "黑色", "绿色" }, 0,
                        new DialogInterface.OnClickListener() {
                            public void onClick(DialogInterface dialog,
                                                int which) {
                               
                                i = which;
                            }
                        })
                .setPositiveButton("确定", new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface dialog, int which) {
                       
                        RelativeLayout rl = (RelativeLayout) findViewById(R.id.rtl);
                        rl.setBackgroundColor(arr[i]);

                    }
                })
                .setNegativeButton("取消", new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface dialog, int which) {
                        dialog.dismiss();
                    }
                });
        dialog = builder.create();
        dialog.show();
    }
}

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">



    <Button
        android:id="@+id/but1"
        style="?android:attr/buttonStyleSmall"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentBottom="true"
        android:layout_centerHorizontal="true"
        android:layout_marginBottom="188dp"
        android:onClick="click"
        android:text="设置背景颜色" />

</androidx.constraintlayout.widget.ConstraintLayout>