Android简单计算器（已消除常见bug）

xml文件：

java文件：

package com.next.calculator1;

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

public class MainActivity extends Activity {
	private TextView textView;
	private String str,num1,num2;
	private double result;
	private boolean addNum;
	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);
		textView = (TextView) findViewById(R.id.textView);
		addNum = true;
	}

	public void onClick(View v){
		str = (String) textView.getText();
		switch (v.getId()) {
		case R.id.btn_cle:
			textView.setText("");
			break;
		case R.id.btn_del:
			if(!str.equals("") && str != null){
				textView.setText(str.substring(0, str.length()-1));
			}
			break;
		case R.id.btn_equ:
			if(str.contains("+")){
				getResult(num1, num2, "+");
			}
			else if(str.contains("-")){
				getResult(num1, num2, "-");
			}
			else if(str.contains("×")){
				getResult(num1, num2, "×");
			}
			else if(str.contains("÷")){
				getResult(num1, num2, "÷");
			}
			else {
				return;
			}
			break;
		case R.id.btn_add:
		case R.id.btn_sub:
		case R.id.btn_mul:
		case R.id.btn_div:
			if (str.contains("+")||str.contains("-")||str.contains("×")||str.contains("÷"))
				return;
			else
				textView.setText(str+((Button)v).getText());
			if(!addNum)
				addNum = true;
			break;
		default:
			if (addNum) {
				textView.setText(str+((Button)v).getText());
			}else{
				textView.setText(((Button)v).getText());
				addNum = true;
			}
			break;
		}
	}
	private void getResult(String num1,String num2,String op) {
		num1 = str.substring(0,str.indexOf(op));
		num2 = str.substring(str.indexOf(op)+1);
		try {
			double n1 = Double.parseDouble(num1);
			double n2 = Double.parseDouble(num2);
			if (op.equals("+")) {
				result = n1+n2;
			}else if(op.equals("-")){
				result = n1-n2;
			}else if(op.equals("×")){
				result = n1*n2;
			}else if(op.equals("÷")){
				result = n1/n2;
			}else {
				return;
			}

			String r = result+"";
			if(r.contains(".")&&r.substring(r.length()-1).equals("0")){
				r = r.substring(0,r.indexOf("."));
			}
			textView.setText(r);
			addNum = false;
		} catch (Exception e) {
			return;
		}
	}
}