CODEWITHSUNDEEP
javaandroid
nygage
nygage

Reputation: 38

findViewById of a Constraint Layout returns null

I have a problem with findViewById using Java in Android Studio. I'm triying to obtain a Constraint Layout to use .addview in it but it returns null.

This is the layout:

<?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:layout_width="match_parent"
    android:layout_height="match_parent"
    android:id="@+id/gameLayout"
    tools:context=".GameActivity">

This is the line with problems:

ConstraintLayout mainLayout = (ConstraintLayout) findViewById(R.id.gameLayout);

And it returns null, what am I doing bad?

Thanks

Edit: Now I'm getting stucked afther this loops, what can be?

protected void generateGameZone(int m, int n){
        LinearLayout[] main_layouts = new LinearLayout[m];
        for(int i=0;i<main_layouts.length;i++){
            main_layouts[i] = new LinearLayout(this);
            main_layouts[i].setOrientation(LinearLayout.HORIZONTAL);
            main_layouts[i].setLayoutParams(new LinearLayout.LayoutParams(30,30));
            mainLayout.addView(main_layouts[i]);
        }
        LinearLayout[][] secondary_layouts = new LinearLayout[m][n];
        for(int i=0;i<secondary_layouts.length;i++){
            for(int j=0;j<secondary_layouts[i].length;j++){
                secondary_layouts[i][j] = new LinearLayout(this);
                secondary_layouts[i][j].setOrientation(LinearLayout.HORIZONTAL);
                secondary_layouts[i][j].setLayoutParams(new LinearLayout.LayoutParams(LinearLayout.LayoutParams.MATCH_PARENT,LinearLayout.LayoutParams.MATCH_PARENT));
                TextView txtBox = new TextView(this);
                txtBox.setLayoutParams(new LinearLayout.LayoutParams(LinearLayout.LayoutParams.WRAP_CONTENT, LinearLayout.LayoutParams.WRAP_CONTENT));
                txtBox.setId(i*10 + j);
                secondary_layouts[i][j].addView(txtBox);
                main_layouts[i].addView(secondary_layouts[i][j]);
            }
        }
    }

I obtain a black screen

Edit2: Black screen solved, now the layout I create with loops its not being showed

Upvotes: 0

Views: 645

Answers (1)

Henry Twist
Henry Twist

Reputation: 5990

From your question it seems like you are trying to add the ConstraintLayout programmatically to your activity. However findViewById(int) called from an Activity tries to find the already existing view in the hierarchy and returns null if it isn't found.

I think what you are looking for is either to inflate the layout using a LayoutInflater and then add it using addView as you suggested, or if this layout represents the root of your activity, use setContentView(int) to let the activity handle the inflation.

Upvotes: 1

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