Android App无法在模拟器中运行

Question

I am unable to run this app on an emulator. It's a simple app to display the count, which can be increased or decreased using buttons. It installs correctly and opens fine but as soon as a button is pressed it closes abnormally displaying "Unfortunately App has stopped working". I am attaching my emulator, environment detail and application code as well.

Starting Point.java class

package com.example.test;
import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;

public class StartingPoint extends Activity {

    int total;
    Button add,minus;
    TextView display;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_starting_point);


        add=(Button)findViewById(R.id.addBtn);
        minus=(Button)findViewById(R.id.delBtn);
        add.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View v) {
                total=total+1;
                display.setText(" " +total);
            }
        });
        minus.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View v) {
                total=total-1;
                display.setText(" " +total);
            }
        });
    }
}

StartingPoint.xml Class

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="${relativePackage}.${activityClass}" >

    <TextView
        android:id="@+id/DisplayTV"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:text="Your total is : "
        android:textSize="45dp" />

    <Button
        android:id="@+id/addBtn"
        style="?android:attr/buttonStyleSmall"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:layout_alignParentLeft="true"
        android:layout_below="@+id/deleteBtn"
        android:layout_marginTop="163dp"
        android:text="ADD" />

    <Button
        android:id="@+id/delBtn"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:layout_alignParentLeft="true"
        android:layout_below="@+id/DisplayTV"
        android:layout_marginTop="179dp"
        android:text="Delete" />

</RelativeLayout>

Console After App Launch

[2015-09-22 01:27:14 - Test] ------------------------------
[2015-09-22 01:27:14 - Test] Android Launch!
[2015-09-22 01:27:14 - Test] adb is running normally.
[2015-09-22 01:27:14 - Test] Performing com.example.test.StartingPoint activity launch
[2015-09-22 01:27:19 - Test] Uploading Test.apk onto device 'emulator-5554'
[2015-09-22 01:27:21 - Test] Installing Test.apk...
[2015-09-22 01:27:37 - Test] Success!
[2015-09-22 01:27:37 - Test] Starting activity com.example.test.StartingPoint on device emulator-5554
[2015-09-22 01:27:39 - Test] ActivityManager: Starting: Intent { act=android.intent.action.MAIN cat=[android.intent.category.LAUNCHER] cmp=com.example.test/.StartingPoint }

Application launches successfully after this but displays errors as the application closed unexpectedly. I am also giving my Emulator details below.

Device: Nexus 4 Target: Android 2.3.3 API lvl: 10 Internal Storage: 200 MiB

Also, there were no errors thrown on the LogCat, response was the same when I tried running the application using my smartphone (lollypop 5.0).

Please help, do let me know if more details are required. Thanks.

Answer 1

You didn't initialize your TextView , make sure to FindViewById it as well before you setText() it.

On top of that, I think you didn't initialize your "total" int variable. When you do

total = total + 1;

Its null, so it crashes

Try setting total = 0; right after your "SetContentView"

Answer 2

Here use this code, this will work.

public class StartingPoint extends Activity {

    int total=0;
    Button add,minus;
    TextView display;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_starting_point);
        display=(TextView)findViewById(R.id.DisplayTV);
        add=(Button)findViewById(R.id.addBtn);
        minus=(Button)findViewById(R.id.delBtn);
        add.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View v) {
                total=total+1;
                display.setText(" " +total);
            }
        });
        minus.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View v) {
                total=total-1;
                display.setText(" " +total);
            }
        });
    }
}