Why the APK crash when I open it

Question

I can not open the APK normally, but the debugger has no serious problems. I consider that the problem may occur in here.

MainActivity.java:

private TextView text;
public static Toast toast = null;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    text = (TextView) findViewById(R.id.text);
    text.setText("IP address : "+getLocalHostIp());

    new ServerListener().start();
}

activity_main.xml:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
    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"
    android:orientation="horizontal"
    tools:context=".MainActivity">

    <TextView
        android:id="@+id/setText"
        android:layout_width="match_parent"
        android:layout_height="51dp"
        android:layout_weight="1" />

</LinearLayout>

from the code you posted m do you want to get the IP address of the device? — No Name, Sep 09 '19 at 12:19
@陳毓凱 Welcome to SO. The preferred way of saying "thanks" around here is to Upvote helpful answers and Accept the one that fixed your issue. — kenny_k, Sep 09 '19 at 13:43

score 2 · Answer 1 · answered Sep 09 '19 at 12:53

You are using the wrong id for textView in your code which is causing the app to crash.

You've defined setText as id for the TextView in your .xml file android:id="@+id/setText", and you are using "text" as the id to map the TextView in your code text = (TextView) findViewById(R.id.text);, which obviously can not be found and is the cause of the problem.

to solve this, do one of the following:

Change text = (TextView) findViewById(R.id.text); to text = (TextView) findViewById(R.id.setText);
or change android:id="@+id/setText" to android:id="@+id/text"

score 0 · Answer 2 · answered Sep 09 '19 at 13:46

0

Your id for TextView is wrong, you can use below code

<TextView
    android:id="@+id/text"
    android:layout_width="match_parent"
    android:layout_height="51dp"
    android:layout_weight="1" />

answered Sep 09 '19 at 13:46

Emad Seliem

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Why the APK crash when I open it

2 Answers2