为什么android一摁键就闪退,为什么一按键就闪退

package com.example.calculatordemo;

import android.R.bool;

import android.support.v7.app.ActionBarActivity;

import android.app.Activity;

import android.os.Bundle;

import android.view.Menu;

import android.view.MenuItem;

import android.view.View;

import android.view.View.OnClickListener;

import android.widget.Button;

import android.widget.EditText;

import android.widget.TextView;

public class MainActivity extends Activity implements OnClickListener {

Button btn_0;

Button btn_1;

Button btn_2;

Button btn_3;

Button btn_4;

Button btn_5;

Button btn_6;

Button btn_7;

Button btn_8;

Button btn_9;

Button btn_point;

Button btn_clear;

Button btn_del;

Button btn_plus;

Button btn_minus;

Button btn_multiply;

Button btn_divide;

Button btn_equal;

EditText et_input;

boolean clear_flag;// 清空标示

@Override

protected void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.activity_main);

btn_0 = (Button) findViewById(R.id.btn_0);

btn_1 = (Button) findViewById(R.id.btn_1);

btn_2 = (Button) findViewById(R.id.btn_2);

btn_3 = (Button) findViewById(R.id.btn_3);

btn_4 = (Button) findViewById(R.id.btn_4);

btn_5 = (Button) findViewById(R.id.btn_5);

btn_6 = (Button) findViewById(R.id.btn_6);

btn_7 = (Button) findViewById(R.id.btn_7);

btn_8 = (Button) findViewById(R.id.btn_8);

btn_9 = (Button) findViewById(R.id.btn_9);

btn_point = (Button) findViewById(R.id.btn_point);

btn_clear = (Button) findViewById(R.id.btn_clear);

btn_del = (Button) findViewById(R.id.btn_del);

btn_plus = (Button) findViewById(R.id.btn_plus);

btn_minus = (Button) findViewById(R.id.btn_minus);

btn_multiply = (Button) findViewById(R.id.btn_multiply);

btn_divide = (Button) findViewById(R.id.btn_divide);

btn_equal = (Button) findViewById(R.id.btn_equal);

EditText et_input = (EditText) findViewById(R.id.et_input);

btn_0.setOnClickListener(this);

btn_1.setOnClickListener(this);

btn_2.setOnClickListener(this);

btn_3.setOnClickListener(this);

btn_4.setOnClickListener(this);

btn_5.setOnClickListener(this);

btn_6.setOnClickListener(this);

btn_7.setOnClickListener(this);

btn_8.setOnClickListener(this);

btn_9.setOnClickListener(this);

btn_point.setOnClickListener(this);

btn_clear.setOnClickListener(this);

btn_del.setOnClickListener(this);

btn_plus.setOnClickListener(this);

btn_minus.setOnClickListener(this);

btn_multiply.setOnClickListener(this);

btn_divide.setOnClickListener(this);

btn_equal.setOnClickListener(this);

}

public void onClick(View v) {

String str = et_input.getText().toString();

switch (v.getId()) {

case R.id.btn_0:

case R.id.btn_1:

case R.id.btn_2:

case R.id.btn_3:

case R.id.btn_4:

case R.id.btn_5:

case R.id.btn_6:

case R.id.btn_7:

case R.id.btn_8:

case R.id.btn_9:

case R.id.btn_point:

if (clear_flag) {

clear_flag = false;

et_input.setText("");

}

et_input.setText(str + ((Button) v).getText());

break;

case R.id.btn_plus:

case R.id.btn_minus:

case R.id.btn_multiply:

case R.id.btn_divide:

if (clear_flag) {

clear_flag = false;

et_input.setText("");

}

et_input.setText(str + " " + ((Button) v).getText() + " ");

break;

case R.id.btn_del:

if (clear_flag) {

clear_flag = false;

et_input.setText("");

} else if (str != null && !str.equals("")) {

et_input.setText(str.substring(0, str.length() - 1));

}

break;

case R.id.btn_clear:

clear_flag = false;

et_input.setText("");

break;

case R.id.btn_equal:

getResult();

break;

}

}

private void getResult() {

String exp = et_input.getText().toString();

if (exp == null || exp.equals("")) {

return;

}

if (!exp.contains(" ")) {

return;

}

if (clear_flag) {

clear_flag = false;

return;

}

clear_flag = true;

double result = 0;

String s1 = exp.substring(0, exp.indexOf(" "));// 运算符前面的内容

String op = exp.substring(exp.indexOf(" ") + 1, exp.indexOf(" ") + 2);// 运算符

String s2 = exp.substring(exp.indexOf(" ") + 3);// 运算符后面的内容

if (!s1.equals("") && !s2.equals("")) {

Double d1 = Double.parseDouble(s1);

Double d2 = Double.parseDouble(s2);

if (op.equals("＋")) {

result = d1 + d2;

} else if (op.equals("－")) {

result = d1 - d2;

} else if (op.equals("×")) {

result = d1 * d2;

} else if (op.equals("÷")) {

if (d2 == 0) {

result = 0;

} else {

result = d1 / d2;

}

}

if (!s1.contains(".") && !s2.contains(".")) {

int r = (int) result;

et_input.setText(r + "");

} else {

et_input.setText(result + "");

}

} else if (!s1.equals("") && s2.equals("")) {

et_input.setText(exp);

} else if (s1.equals("") && !s2.equals("")) {

Double d2 = Double.parseDouble(s2);

if (op.equals("＋")) {

result = 0 + d2;

} else if (op.equals("－")) {

result = 0 - d2;

} else if (op.equals("×")) {

result = 0;

} else if (op.equals("÷")) {

result = 0;

}

if (!s2.contains(".")) {

int r = (int) result;

et_input.setText(r + "");

} else {

et_input.setText(result + "");

}

} else {

et_input.setText("");

}

}

}