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Thread: need help understanding code

  1. #1
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    Default need help understanding code

    So I am studying how to build android apps by myself and I am stuck trying to understand some of the life of codes for this particular code:

    package com.ebookfrenzy.javalayout;
     
    import android.support.v7.app.AppCompatActivity;
    import android.os.Bundle;
    import android.view.Menu;
    import android.view.MenuItem;
    import android.widget.Button;
    import android.widget.RelativeLayout;
     
    public class JavaLayoutActivity extends AppCompatActivity
    {
        @Override
        protected void onCreate(Bundle savedInstanceState)
        {
            super.onCreate(savedInstanceState);
            Button myButton = new Button(this);
            RelativeLayout myLayout = new RelativeLayout(this);
            myLayout.addView(myButton);
            setContentView(myLayout);
        }
    }

    This is to create a simple button. However, I do not under what "this" in:
    Button myButton = new Button(this);
    RelativeLayout myLayout = new RelativeLayout(this);

    refers to, and the book does not say.

  2. #2
    Super Moderator Norm's Avatar
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    Default Re: need help understanding code

    under what "this" in
    In standard java the this variable holds a reference to the the class it is in. For the posted code, this would refer to the instance of the JavaLayoutActivity class.
    If you don't understand my answer, don't ignore it, ask a question.

  3. #3
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    Default Re: need help understanding code

    Ah, I see now. Thanks

    --- Update ---

    I have one more question (I don't want to create another thread since it is basically more on understanding the code)

    This is the same code, but added more to create a background of blue and a yellow button that says "PRESS ME".

    package com.ebookfrenzy.javalayout;
     
    import android.annotation.SuppressLint;
    import android.support.v7.app.AppCompatActivity;
    import android.os.Bundle;
    import android.view.Menu;
    import android.view.MenuItem;
    import android.widget.Button;
    import android.widget.RelativeLayout;
    import android.graphics.Color;
    import android.widget.EditText;
    import android.content.res.Resources;
    import android.util.TypedValue;
     
    public class JavaLayoutActivity extends AppCompatActivity
    {
        @SuppressLint("ResourceType")
        @Override
        protected void onCreate(Bundle savedInstanceState)
        {
            super.onCreate(savedInstanceState);
     
            //sets button
            Button myButton = new Button(this);
            myButton.setText("Press Me");
            myButton.setBackgroundColor(Color.YELLOW);
     
            //sets background color
            RelativeLayout myLayout = new RelativeLayout(this);
            myLayout.setBackgroundColor(Color.BLUE);
     
            EditText myEditText = new EditText(this);
     
            myButton.setId(1);
            myEditText.setId(2);
     
            //sets location of the button relative to the screen
            RelativeLayout.LayoutParams buttonParams = new RelativeLayout.LayoutParams(
     
                    RelativeLayout.LayoutParams.WRAP_CONTENT, RelativeLayout.LayoutParams.WRAP_CONTENT
            );
     
            RelativeLayout.LayoutParams textParams = new RelativeLayout.LayoutParams(
     
                    RelativeLayout.LayoutParams.WRAP_CONTENT, RelativeLayout.LayoutParams.WRAP_CONTENT
            );
     
            textParams.addRule(RelativeLayout.ABOVE, myButton.getId());
     
            textParams.addRule(RelativeLayout.CENTER_HORIZONTAL);
            textParams.setMargins(0, 0, 0, 80);
     
            buttonParams.addRule(RelativeLayout.CENTER_HORIZONTAL);
            buttonParams.addRule(RelativeLayout.CENTER_VERTICAL);
     
            myLayout.addView(myButton, buttonParams);
            myLayout.addView(myEditText, textParams);
            setContentView(myLayout);
        }
    }

    My question is, for:
    myButton.setId(1);
    myEditText.setId(2);
    there was an error, and automatically is created something called: @SuppressLint("ResourceType")
    What does this mean? and why was there an error for the setId methods?

  4. #4
    Super Moderator Norm's Avatar
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    Default Re: need help understanding code

    Have you read the API doc for the setId method? What is it supposed to do? Why is it in the code?
    If you don't understand my answer, don't ignore it, ask a question.

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