Incorrect clip rect in onDraw()?

by Leisuresuit Larry » Fri, 10 Apr 2009 01:40:34 GMT


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 Hi all,

We came across a strange behavior. The clip rect of our custom view is
getting reset to its entire visible region, if we change the value of
another view.

Below is a sample app to demonstrate the behavior:

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

<com.test.MyView
    android:id="@+id/view"
    android:layout_width="fill_parent"
    android:layout_height="100px" />

<TextView
    android:id="@+id/text"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content" />

</LinearLayout>

ClipTest.java:
package com.test;

import android.app.Activity;
import android.os.Bundle;
import android.view.KeyEvent;
import android.widget.TextView;

public class ClipTest extends Activity {
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
    }


    @Override
    public boolean onKeyDown(int keyCode, KeyEvent event) {
        TextView tv = (TextView)findViewById(R.id.text);
        tv.setText("Test");

        findViewById(R.id.view).invalidate(100, 0, 150, 75);
        return true;
    }
}

MyView.java:
package com.test;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Rect;
import android.util.AttributeSet;
import android.view.View;

public class MyView extends View {

    public MyView(Context context) {
        super(context);
    }

    public MyView(Context context, AttributeSet attrs) {
        super(context, attrs);
    }

    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);

        Rect clip = canvas.getClipBounds();
        System.out.println("clip " + clip);
    }
}

If you run the above app, MyView.onDraw() prints "clip Rect(0, 0, 320,
100)". If you comment out "tv.setText("Test");", then MyView.onDraw()
prints "clip Rect(100, 0, 150, 75)".

Why does setting the TextView's text affect MyView's clip rect? How
can we get the correct clip rect in MyView.onDraw()? Thanks for any
help!

Larry

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Incorrect clip rect in onDraw()?

by Romain Guy » Fri, 10 Apr 2009 02:46:52 GMT


 etText() invalidates the TextView entirely and when two invalidates
happen in the same UI event (as it is the case in your code), the
invalidate region becomes the union of the two original invalidate
regions.

On Wed, Apr 8, 2009 at 6:40 PM, Leisuresuit Larry <larrywan...@gmail.com> wrote:



--
Romain Guy
Android framework engineer
romain...@android.com

Note: please don't send private questions to me, as I don't have time
to provide private support. All such questions should be posted on
public forums, where I and others can see and answer them

--~--~---------~--~----~------------~-------~--~----~


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Incorrect clip rect in onDraw()?

by Leisuresuit Larry » Tue, 14 Apr 2009 02:30:56 GMT


 hanks for the explanation. We worked around this behavior send
separate messages to a Handler on the UI thread. I'm curious, though,
to why Android doesn't handle the invalidate regions separately.

On Apr 9, 11:46am, Romain Guy <romain...@google.com> wrote:
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Incorrect clip rect in onDraw()?

by Dianne Hackborn » Tue, 14 Apr 2009 02:45:53 GMT


 e very deliberately coalesce multiple invalidates into a single draw for
performance reasons (so we can perform a draw of the hierarchy once instead
of twice). This also avoids showing the UI in partial states, where one
part of the window has been updated to a new state but another part hasn't.
You probably shouldn't be working around this.

On Mon, Apr 13, 2009 at 11:30 AM, Leisuresuit Larry
<larrywan...@gmail.com>wrote:



--
Dianne Hackborn
Android framework engineer
hack...@android.com

Note: please don't send private questions to me, as I don't have time to
provide private support, and so won't reply to such e-mails. All such
questions should be posted on public forums, where I and others can see and
answer them.

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What I understood is, you have an XML, where you have defined some
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addPreferencesFromResource).
Now, there is one checkbox type preference, which you dont want your
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I am assuming that you are willing to change that preference from code
(otherwise, how is it going to be changed?)

So, just remove that checkbox preference from your XML. Then, your
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Then, add/read/modify that preference from code.
In preferences, there is an edit() method, which return an Editor. You
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Dont forget to call commit().


Regards
Sarwar Erfan





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