Question

I have a canvas, in which I want to paint several rectangles, I can paint with canvas in an InternalView, but I need to paint in a scrollview, I tried with this code, but some have evil.
This is the code:

   package prueba.android.ondraw;

import android.app.Activity;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.os.Bundle;
import android.view.View;
import android.view.Window;
import android.view.WindowManager;
import android.widget.LinearLayout;
import android.widget.ScrollView;
import android.widget.TextView;

public class Prueba_ondrawActivity extends Activity {
    @Override
    public void onCreate(Bundle savedInstanceState) {
        requestWindowFeature(Window.FEATURE_NO_TITLE);
        getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN, WindowManager.LayoutParams.FLAG_FULLSCREEN);
        super.onCreate(savedInstanceState);

        LinearLayout layout = (LinearLayout) findViewById(R.id.layout);
        setContentView(R.layout.main);

        MyView v = new MyView(this);
        layout.addView(v);

    }
    private class MyView extends View{
        public MyView(Context context) {
            super(context);
        }
        protected void onDraw(Canvas canvas) {
            int j = 0;
            for(int i=0;i<10;i++){
                super.onDraw(canvas);
                Paint paint = new Paint();
                paint.setColor(Color.CYAN);
                paint.setAntiAlias(true);
                canvas.drawRect(0, j,50,50, paint);
                j= j+100;
            }
        }
    }
}

Main.xml

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

    <ScrollView
        android:id="@+id/scrollView1"
        android:layout_width="150dp"
        android:layout_height="400dp"
        android:layout_marginLeft="100dp" >
        <LinearLayout
            android:id="@+id/layout"
            android:layout_width="match_parent"
            android:layout_height="wrap_content">
        </LinearLayout>
    </ScrollView>

</LinearLayout>

Help please, thank you!

Answer 1

You are doing some strange things in your code:
first you try to find a view (findViewById()) before you have used setContentView() (sv will always be null here, because there are no views yet), then you replace that View with a new ScrollView (which you don’t use), and finally you set the content to a layout.

Instead what you probably want to do is create your own View, and then use that inside a ScrollView?

In your ScrollView, you have a layout, this will need an ID:

<ScrollView
    android:id="@+id/scrollView1"
    android:layout_width="150dp"
    android:layout_height="400dp"
    android:layout_marginLeft="100dp" >
    <LinearLayout
        android:id="@+id/layout"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"/>
</ScrollView>

Then you find this layout in code:

setContentView(R.layout.main);
LinearLayout layout = (LinearLayout) findViewById(R.id.layout);
//Create a new instance of MyView...
MyView v = new MyView(this);
//...And add it to the layout:
layout.addView(v);

And you can define your own MyView like this:

private class MyView extends View{
    //Your onDraw() method here.
}

(Notice that I call the custom View MyView. This is because android already have a class named View, so it could cause lots of confusion if you give classes names that already exist)