App not showing on screen on Android?

Question

Java

I'm just a schoolboy learning java and I met a problem when developing an application the
problem is that the application does not want to be displayed on the screen of my phone
although it is displayed on the preview screen in AS
here is my XML code:

<?xml version="1.0" encoding="utf-8"?>
<TableLayout
    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="com.example.mafcv.MainActivity">


    <TableRow
        android:layout_width="match_parent"
        android:layout_height="wrap_content">

        <EditText
            android:id="@+id/etP"
            android:layout_width="133dp"
            android:layout_height="wrap_content"
            android:ems="10"
            android:inputType="textPersonName"
            android:text="Name" />

        <Button
            android:id="@+id/btn1"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Button" />

        <Button
            android:id="@+id/btn2"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Button" />

    </TableRow>

    <TableRow
        android:layout_width="166dp"
        android:layout_height="11dp">

        <Button
            android:id="@+id/btna"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:text="Button" />

        <Button
            android:id="@+id/btnb"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Button" />

        <Button
            android:id="@+id/btnc"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Button" />
    </TableRow>

    <TableRow
        android:layout_width="312dp"
        android:layout_height="58dp">

        <TextView
            android:id="@+id/textView"
            android:layout_width="206dp"
            android:layout_height="40dp"
            android:text="TextView"
            android:textAppearance="@style/TextAppearance.AppCompat.Medium" />
    </TableRow>

    <TableRow
        android:layout_width="match_parent"
        android:layout_height="match_parent" >

        <TextView
            android:id="@+id/textView5"
            android:layout_width="wrap_content"
            android:layout_height="40dp"
            android:text="TextView"
            android:textAppearance="@style/TextAppearance.AppCompat.Medium" />
    </TableRow>

    <TableRow
        android:layout_width="match_parent"
        android:layout_height="match_parent" >

        <TextView
            android:id="@+id/textView6"
            android:layout_width="wrap_content"
            android:layout_height="40dp"
            android:text="TextView"
            android:textAppearance="@style/TextAppearance.AppCompat.Medium" />
    </TableRow>

    <TableRow
        android:layout_width="match_parent"
        android:layout_height="match_parent" >

        <TextView
            android:id="@+id/textView7"
            android:layout_width="wrap_content"
            android:layout_height="40dp"
            android:text="TextView"
            android:textAppearance="@style/TextAppearance.AppCompat.Medium" />
    </TableRow>
</TableLayout>

here is the java:

ckage com.example.mafcv;

import android.support.constraint.ConstraintLayout;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.Gravity;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.EditText;
import android.widget.LinearLayout;
import android.widget.Switch;
import android.widget.TextView;

public class MainActivity extends AppCompatActivity implements View.OnClickListener{
    Button b1;
    Button b2;
    Button ba;
    Button bb;
    Button bc;
    EditText et;
    TextView tv;
    TextView tvD;
    TextView tvX1;
    TextView tvX2;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        et=(EditText) findViewById(R.id.etP);
        b1=(Button) findViewById(R.id.btn1);
        b2=(Button) findViewById(R.id.btn2);
        ba=(Button) findViewById(R.id.btna);
        bb=(Button) findViewById(R.id.btnb);
        bc=(Button) findViewById(R.id.btnc);

    }


    public void onClick(View v) {
            }
        }

though there is absolutely nothing done there,
even in listner there is nothing
api=27
phone=Samsung Galaxy j3 .

Answer 1

You need to call setContentView() and pass the id of this layout to it.
It's amazing that the app does not crash at startup.