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Ok I'm a newbie at Android programming, have a hard time with the graphics part. Understand the beauty of creating layout in XML file, but lost how to access various elements, especially a View element to draw on it.

See example of my layout main.xml here;

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
 android:id="@+id/root" android:orientation="vertical"
 android:layout_width="fill_parent" android:layout_height="fill_parent">

 <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
  android:layout_width="fill_parent" android:layout_height="wrap_content">

  <TextView xmlns:android="http://schemas.android.com/apk/res/android"
   android:id="@+id/Title" android:text="App title"
   android:layout_width="fill_parent" android:layout_height="wrap_content"
   android:textColor="#000000"
   android:background="#A0A0FF"/>
 </LinearLayout>

 <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
  android:id="@+id/PaperLayout" android:layout_width="fill_parent" 
  android:layout_height="0dp" android:layout_weight="1" 
  android:orientation="horizontal" android:focusable="true">

  <View android:id="@+id/Paper" android:layout_width="fill_parent" 
   android:layout_height="fill_parent" />
 </LinearLayout>


 <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
  android:layout_width="fill_parent" android:layout_height="wrap_content">

  <Button android:id="@+id/File" android:layout_width="fill_parent"
   android:layout_weight="1" android:layout_height="34dp"
   android:layout_alignParentTop="true" android:layout_centerInParent="true"
   android:clickable="true" android:textSize="10sp" android:text="File" />

  <Button android:id="@+id/Edit" android:layout_width="fill_parent"
   android:layout_weight="1" android:layout_height="34dp"
   android:clickable="true" android:textSize="10sp" android:text="Edit" />
 </LinearLayout>

</LinearLayout>

As you can see I have a custom app title bar, then a View filling middle, and finally two buttons in bottom. Catching button events and responding to, for example changing title bar text and changing View background color works fine, but how the heck do I access and more importantly draw on the view defined in main.xml

UPDATE: Thank you very much for your suggestion, however besides that I need a View, not ImageView and you are missing a parameter on canvas.drawText and an ending bracket, it does not work.

Now this is most likely because you missed the fact that I am a newbie and assuming I can fill in any blanks.

Now first of all I do NOT understand why in my main.xml layout file I can create a View or even a SurfaceView element, which is what I need, but according to your solution I don't even specify the View like

Anyways I edited my main.xml according to your solution, and slimmed it down a bit for simplicity;

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
 android:id="@+id/root" android:orientation="vertical"
 android:layout_width="fill_parent" android:layout_height="fill_parent">

 <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
  android:layout_width="fill_parent" android:layout_height="wrap_content">

  <TextView xmlns:android="http://schemas.android.com/apk/res/android"
   android:id="@+id/Title" android:text="App title"
   android:layout_width="fill_parent" android:layout_height="wrap_content"
   android:textColor="#000000"
   android:background="#A0A0FF"/>
 </LinearLayout>

 <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
  android:id="@+id/PaperLayout" android:layout_width="fill_parent" 
  android:layout_height="0dp" android:layout_weight="1" 
  android:orientation="horizontal" android:focusable="true">

    <com.example.MyApp.CustomView 
    android:id="@+id/Paper" 
    android:layout_width="fill_parent" 
    android:layout_height="fill_parent" />
    <com.example.colorbook.CustomView/>

 </LinearLayout>

 <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
  android:layout_width="fill_parent" android:layout_height="wrap_content">

  <Button android:id="@+id/File" android:layout_width="fill_parent"
   android:layout_weight="1" android:layout_height="34dp"
   android:layout_alignParentTop="true" android:layout_centerInParent="true"
   android:clickable="true" android:textSize="10sp" android:text="File" />

 </LinearLayout>

</LinearLayout>

In my main java file, MyApp.java, I added this after OnCreate;

public class CustomView extends ImageView {
  @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        canvas.drawText("Your Text", 1, 1, null);
    }
}

But I get error on the "CustomView" part; "Implicit super constructor ImageView() is undefined for default constructor.Must define an explicit constructor"

Eclipse suggests 3 quick fixes about adding constructor, but none helps, well it removes error but gives error on app when running.

I hope somebody can break this down for me and provide a solution, and perhaps explain why I can't just create a View element in my main.xml layout file and draw on it in code.

UPDATE: Ok I am still trying to use your solution, which is still giving me problems and various errors. But first and foremost I still do NOT understand why I have to create a custom class to use in my layout, when I have to option to even use the wysiwyg layout editor to insert a View element and "just" draw on that in my main, well for now only code file. So pleeeeeease someone answer me that one.

Anyways now I have;

package com.example.myapp;

import com.example.myapp.CustomView;

and here comes other import

  public class MyApp extends Activity { 

rest of code including OnCreate

And i created a new class, new file CustomView.Java, where I directly pasted your code so it looks like;

package com.example.myapp;

public class CustomView extends ImageView {
    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        Paint paint = new Paint();
        paint.setARGB(255, 150, 205, 129);
        paint.setTextSize(20);
        canvas.drawText("Your Text", 1, 1, paint);
    }
}

Ok so this class code wants me to add imports for ImageView, Canvas, and Paint, which I did, and then again I am back to the error the public class "CustomView" part; "Implicit super constructor ImageView() is undefined for default constructor.Must define an explicit constructor".

I appreciate you trying to help me, THANKS!

share|improve this question
 
No need for "Android programming" in your title, thats what tags are for. –  L0rdAli3n Dec 28 '10 at 18:34
 
Ok thanks, but I weren't allowed to use tag "Programming" –  DKDiveDude Dec 28 '10 at 18:54
 
This is a programmingside, so android is enough as tag. Also consider to mark a answer as accepted, to increase your acceptrate. –  L0rdAli3n Dec 28 '10 at 21:31
 
But of course I will mark the answer as accepted, AFTER I have tested the provided solution. Is that ok with you or do you prefer me to accept the answer before I tested it works? –  DKDiveDude Dec 29 '10 at 10:38
 
No, no, no. Of course you test it first! –  L0rdAli3n Dec 29 '10 at 10:40
add comment

3 Answers

up vote 2 down vote

To draw on a view, creat your own custom view.

To do so, you need to add a new class. With eclipse it's just File->New->Class and there you go. Override the onDraw()-Method to fit your needs and add your CustomView to your Layout: 

public class CustomView extends ImageView {
    // The needed constructors:
    public CustomView(Context context) {
        super(context);
    }
    public CustomView(Context context, AttributeSet attrs) {
        super(context, attrs);
    }
    public CustomView(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
    }



@Override
protected void onDraw(Canvas canvas) {
    super.onDraw(canvas);
    Paint paint = new Paint();
    paint.setARGB(255, 150, 205, 129);
paint.setTextSize(20);
    canvas.drawText("Your Text", xposition, yposition, paint);
}




}

In your xml-File you add your CustomView like this:

<com.example.CustomView
            android:id="@+id/yourID"
            android:layout_alignParentRight="true"
            android:layout_alignParentBottom="true"
            android:layout_margin="10dp"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content">
        </com.example.CustomView>

If you wan't to draw onto a drawable from your res-Folder, specifiy the "src"-parameter of your customView.

share|improve this answer
 
That for your suggestion, however besides that I need a View, not ImageView and you are missing an ending bracket, it does not work. –  DKDiveDude Dec 29 '10 at 11:21
 
Well, it seams you have to learn some java basics befor writing your own app... I will improve my answer to clarify things. Be patient. Sorry for the missing bracket, I slimed down my example and slmied down to much :) –  L0rdAli3n Dec 29 '10 at 12:07
 
As you said, you wan't to draw, therefore you don't have to care if you draw on a view or on a imageview, the result is the same. –  L0rdAli3n Dec 29 '10 at 12:14
 
Still not working, see revised question above –  DKDiveDude Dec 29 '10 at 13:12
 
When the error says "Must define an explicit constructor" then why don't you just define one? Please learn some basic's about Java and Android before you mess up with CustomViews and more advanced stuff. I edited my answer, so it includes the needed constructors, should fix your error. –  L0rdAli3n Dec 29 '10 at 14:58
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up vote 0 down vote

override the onCreate method and then use the method findViewById. For example to use and modify the view background color use the following :

View v = (View)findViewById(R.id.Paper);
v.setBackgroundColor(myColor);

Similarly modify any other view/Widget defined in your layout

share|improve this answer
 
Also thank you very much for the reply. It seems that I did not make it clear in my question, that I am actually able to change the background color just fine, by doing doing both what you and Axarydax are suggesting. My real question is now how do I draw graphics on that View? –  DKDiveDude Dec 28 '10 at 18:23
 
I would go with what L0rdAli3n said in the above post –  frieza Dec 29 '10 at 5:04
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up vote 0 down vote

to use the view defined in main.xml in an Activity, override Activity's onCreate method such as:

public void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  setContentView(R.layout.main);

}

edit: sorry, I misread "draw on view" as "draw view" in your question :) See L0rdAli3n's answer for that.

share|improve this answer
 
Thanks for the reply, however that part I do know ;) And like I wrote I can change the View elements background color, but how do I actually draw graphics on that View? –  DKDiveDude Dec 28 '10 at 18:19
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