正在编写一个简单的计算器,按钮点击出现问题,详情见下!请指教

点击按钮后无法在TextView中显示出对应的内容.
源码如下:
package com.example.xingpengfei.calculator;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity implements View.OnClickListener{

private TextView inputnum;
private Button button0;
private Button button1;
private Button button2;
private Button button3;
private Button button4;
private Button button5;
private Button button6;
private Button button7;
private Button button8;
private Button button9;
private Button button10;
private Button button11;
private Button button12;
private Button button13;
private Button button14;
private Button button15;
private Button button16;
private Button button17;
private  String s="";

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    inputnum=(TextView)findViewById(R.id.input_num);
    button0=(Button)findViewById(R.id.button0);
    button1=(Button)findViewById(R.id.button1);
    button2=(Button)findViewById(R.id.button2);
    button3=(Button)findViewById(R.id.button3);
    button4=(Button)findViewById(R.id.button4);
    button5=(Button)findViewById(R.id.button5);
    button6=(Button)findViewById(R.id.button6);
    button7=(Button)findViewById(R.id.button7);
    button8=(Button)findViewById(R.id.button8);
    button9=(Button)findViewById(R.id.button9);
    button10=(Button)findViewById(R.id.button10);
    button11=(Button)findViewById(R.id.button11);
    button12=(Button)findViewById(R.id.button12);
    button13=(Button)findViewById(R.id.button13);
    button14=(Button)findViewById(R.id.button14);
    button15=(Button)findViewById(R.id.button15);
    button16=(Button)findViewById(R.id.button16);
    button17=(Button)findViewById(R.id.button17);
}
@Override
public void onClick(View view) {
    switch (view.getId())
    {
        case R.id.button0:
            s+=0;
            inputnum.setText(s);
            break;
        case R.id.button1:{
            s+=1;
            inputnum.setText(s);
            break;
        }
        case R.id.button2:
            s+=2;
            inputnum.setText(s);
            break;
        case R.id.button3:
            s+=3;
            inputnum.setText(s);
            break;
        case R.id.button4:
            s+=4;
            inputnum.setText(s);
            break;
        case R.id.button5:
            s+=5;
            inputnum.setText(s);
            break;
        case R.id.button6:
            s+=6;
            inputnum.setText(s);
            break;
        case R.id.button7:
            s+=7;
            inputnum.setText(s);
            break;
        case R.id.button8:
            s+=8;
            inputnum.setText(s);
            break;
        case R.id.button9:
            s+=9;
            inputnum.setText(s);
            break;
        case R.id.button10:
            s+="+";
            inputnum.setText(s);
            break;
        case R.id.button11:
            s+="-";
            inputnum.setText(s);
            break;
        case R.id.button12:
            s+="*";
            inputnum.setText(s);
            break;
        case R.id.button13:
            s+="÷";
            inputnum.setText(s);
            break;
        case R.id.button14:
            s+=".";
            inputnum.setText(s);
            break;
        case R.id.button15:
            //start
            inputnum.setText("");
            break;
        case R.id.button16:    //delete

            inputnum.setText("");
            break;
        case R.id.button17:  //=

            inputnum.setText("");
            break;

    }
}

}

虽然你的Activity去实现了OnClickListener接口但是你还需要去指定每个button的点击事件：
button.setOnclickListener(this)

XML如下:
<?xml version="1.0" encoding="utf-8"?>
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
tools:context="com.example.xingpengfei.calculator.MainActivity">

<TextView
    android:id="@+id/input_num"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:hint="0."
    android:textSize="20dp"
    android:gravity="right"
    android:layout_marginTop="150dp"
    />
<TableLayout
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:stretchColumns="0,1,2,3"
    >
    <TableRow>
        <Button
            android:id="@+id/button7"
            android:layout_below="@+id/input_num"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="7"
            />
        <Button
            android:id="@+id/button8"
            android:layout_below="@+id/input_num"
            android:layout_toRightOf="@+id/button7"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="8"
            />
        <Button
            android:id="@+id/button9"
            android:layout_below="@+id/input_num"
            android:layout_toRightOf="@+id/button8"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="9"
            />
        <Button
            android:id="@+id/button10"
            android:layout_below="@+id/input_num"
            android:layout_toRightOf="@+id/button9"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="+"
            />
     </TableRow>

     <TableRow>

        <Button
            android:id="@+id/button4"
            android:layout_below="@+id/button7"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="4"
            />
        <Button
            android:id="@+id/button5"
            android:layout_below="@id/button7"
            android:layout_toRightOf="@id/button4"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="5"
            />
        <Button
            android:id="@+id/button6"
            android:layout_below="@id/button7"
            android:layout_toRightOf="@id/button5"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="6"
            />
        <Button
            android:id="@+id/button11"
            android:layout_below="@id/button7"
            android:layout_toRightOf="@id/button6"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="-"
            />
</TableRow>

<TableRow>
        <Button
            android:id="@+id/button1"
            android:layout_below="@id/button4"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="1"
            />
        <Button
            android:id="@+id/button2"
            android:layout_below="@id/button4"
            android:layout_toRightOf="@id/button1"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="2"
            />
        <Button
            android:id="@+id/button3"
            android:layout_below="@id/button4"
            android:layout_toRightOf="@id/button2"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="3"
            />
        <Button
            android:id="@+id/button12"
            android:layout_below="@id/button4"
            android:layout_toRightOf="@id/button3"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="*"
            />
</TableRow>

<TableRow>
        <Button
            android:id="@+id/button0"
            android:layout_below="@id/button1"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="0"
           android:layout_span="2" />
        <Button
            android:id="@+id/button14"
            android:layout_below="@id/button1"
            android:layout_toRightOf="@id/button0"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="."
            />
        <Button
            android:id="@+id/button13"
            android:layout_below="@id/button12"
            android:layout_toRightOf="@id/button14"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="÷"
            />
     </TableRow>

     <TableRow>
        <Button
            android:id="@+id/button15"
            android:layout_below="@id/button0"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:textAllCaps="false"
            android:textColor="#00dd00"
            android:text="start"
            android:layout_span="2"
            />
        <Button
            android:id="@+id/button16"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_below="@id/button0"
            android:layout_toRightOf="@id/button15"
            android:textColor="#dd00"
            android:textAllCaps="false"
            android:text="delete"
            />
        <Button
            android:id="@+id/button17"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_below="@id/button0"
            android:layout_toRightOf="@id/button16"
            android:text="="
            />
    </TableRow>
</TableLayout>