求圆的面积

网络111 刘修军

本例子简单了解Buutton、TextView、EditText、对话框的用法。

功能：计算圆的面积，当输入非数字时，会弹出一个提示框，提示用户输入数字。

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="vertical" >


    <EditText
        android:id="@+id/inputR"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" >

        <requestFocus />
    </EditText>


    <TextView
        android:id="@+id/circleArea"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="TextView" />


    <Button
        android:id="@+id/compute"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Button" />

</LinearLayout>

                

import java.text.DecimalFormat;

import android.app.Activity;
import android.app.AlertDialog;
import android.app.AlertDialog.Builder;
import android.content.DialogInterface;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;

public class CircleAreaActivity extends Activity implements OnClickListener {
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        inputR=(EditText) findViewById(R.id.inputR);
        circleArea=(TextView) findViewById(R.id.circleArea);
        compute=(Button) findViewById(R.id.compute);
        compute.setOnClickListener(this);
    }
    EditText inputR;
    TextView circleArea;
    Button compute;
    @Override
    public void onClick(View arg0) {
        // TODO Auto-generated method stub
        try
        {
            float area,r;
            r=Float.parseFloat(inputR.getText().toString());
            area=(float) (Math.PI*r*r);   //圆的面积
            DecimalFormat de=new DecimalFormat("0.00");  // 格式转换
            circleArea.setText(de.format(area).toString());
            
        }
        catch(Exception e)
        {
            AlertDialog.Builder  alert=new AlertDialog.Builder(this);
            alert.setTitle("提示");
            alert.setMessage("非数字字符，请输入数字！");
            alert.setPositiveButton("确定",new DialogInterface.OnClickListener() {
                
                @Override
                public void onClick(DialogInterface dialog, int which) {
                    // TODO Auto-generated method stub
                    inputR.setText("");// 清空EditTExt
                }
            });
            alert.show(); //显示对话框
        }
        
    }
}