I am looking for an easy way to animate custom views in Android. I am trying to avoid using the animator object but want to work with raw threads. What I have done is created a custom view by creating a class that extends android.view.View. I then override the onDraw method and use the canvas to draw a rect. What I would like is the rect to shrink, so I keep a variable that represents the x value of the right hand side of the rectangle. I would then like the the rectangle's right edge shrink in over time. What I would have liked to do is create a new thread, start it and have it change the value of the rectangle. That all works except the view doesn't get updated until you call View.invalidate. The problem is that I can't call that from the thread that I spawned because it is not the UI thread. I read solutions on using Handlers... but I am still unsure if that is the correct solution and then how to use them.
package com.example.practicum;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Rect;
import android.os.Handler;
import android.os.Message;
import android.util.AttributeSet;
import android.view.View;
public class TimerControl extends View implements Runnable, Handler.Callback
{
private Paint paint;
private Rect rect;
private Thread t;
private Handler h;
public TimerControl(Context context, AttributeSet attrs)
{
super(context, attrs);
// TODO Auto-generated constructor stub
paint = new Paint();
paint.setColor(Color.BLUE);
rect = new Rect(0,0,60,60);
t = new Thread(this);
t.start();
h = new Handler(this);
//h.post(this);
}
@Override
public void onDraw(Canvas canvas)
{
canvas.drawRect(rect, paint);
}
@Override
public void run()
{
rect.right = rect.right-1;
while(true)
{
rect.right = rect.right-1;
this.invalidate();
try
{
Thread.sleep(5000);
h.sendEmptyMessage(0);
}
catch (InterruptedException e)
{
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
@Override
public boolean handleMessage(Message msg)
{
return false;
}
}