setBackgroundColor 使 Android 应用程序崩溃

Question

I recently made a small app that should change the background color & text of the application when a certain amount of money is generated (here 100000). However, whenever I go past 10000, the application crashes. I am not sure why and can not get around it. I saw that this problem is with background color only because it is otherwise displaying text correctly.

Here is the XML for activity_main

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/Trial"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="#EC5353"
    tools:context=".MainActivity">

    <TextView
        android:id="@+id/Title"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="92dp"
        android:gravity="center"
        android:text="@string/Title"
        android:textSize="24sp"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <TextView
        android:id="@+id/money"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="72dp"
        android:text="@string/moneyPresent"
        android:textSize="22sp"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.498"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/Title" />

    <Button
        android:id="@+id/moneyGenerator"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="72dp"
        android:background="#FFFFFF"
        android:backgroundTint="#732424"
        android:backgroundTintMode="multiply"
        android:text="@string/generateMoneyButton"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/money" />

    <TextView
        android:id="@+id/richTag"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="60dp"
        android:text="@string/grind_boi"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.498"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/moneyGenerator" />

</androidx.constraintlayout.widget.ConstraintLayout>

Here is my Java Code (Omitted the packages as it would take a lot of space. Do tell me if anyone wants to read it.)

public class MainActivity extends AppCompatActivity {
    private Button makeMoney;
    private int totalMoney=0;
    private TextView moneyText;
    private TextView richAlert;
    private ConstraintLayout background;
    NumberFormat currency=NumberFormat.getCurrencyInstance(new Locale("en","in"));

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        makeMoney = findViewById(R.id.moneyGenerator);
        moneyText=findViewById(R.id.money);
        richAlert=findViewById(R.id.richTag);

        makeMoney.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                totalMoney+=1000;
                moneyText.setText(currency.format(totalMoney));
                Log.d("MoneyTag", "Money Made: "+totalMoney);
                Toast.makeText(getApplicationContext(),"Total Money= \u20B9"+totalMoney,Toast.LENGTH_LONG)
                        .show();
                if(totalMoney>=10000) {
                    richAlert.setText("Welcome to moneyland bro 😁");
                    background.setBackgroundColor(16776960);
                }
            }
        });
    }
}

Answer 1

you haven't defined "background" view in the above. to use .setBackgroundColor you need to use it with some view

try making object of layout view then change the color of that layout

 mConstraintLayout =         
(ConstraintLayout)findViewById(R.id.Trial);
 makeMoney = findViewById(R.id.moneyGenerator);
    moneyText=findViewById(R.id.money);
    richAlert=findViewById(R.id.richTag);





if(totalMoney>=10000) {
                richAlert.setText("Welcome to moneyland bro 😁");
                 mConstraintLayout.setBackgroundColor(ContextCompat.getColor(this, R.color.yellow));

Answer 2

    makeMoney = findViewById(R.id.moneyGenerator);
    moneyText=findViewById(R.id.money);
    richAlert=findViewById(R.id.richTag);

You're finding all the views, except background( ConstraintLayout ), that's why it is throwing NullPointerException (Most likely, because you haven't attached logs).

You need to find the layout first

background = findViewById(R.id.Trial);

in onCreate .

Answer 3

 background = findViewById(R.id.Trial);

只需找到布局和空指针异常将被删除