Several ways Android uses Alpha to achieve gradient effects

Principle: The gradient effect is achieved by changing the alpha value of the control transparency

Method One: Using XML

Step one: First, we want to create an. xml file in the Anim folder under the Res folder (here I created Alpha.xml)

Set start transparency at 0.0 (transparent): android:fromalpha= "0.0"

Set End Transparency 1.0 (opaque): android:toalpha= "1.0"

<alpha

Xmlns:android= "Http://schemas.android.com/apk/res/android"

Android:fromalpha= "0.0"

Android:toalpha= "1.0"

Android:duration= ">"

</alpha>

Step two: Next you will use the animation class to achieve the effect

@Override

protected void OnCreate (Bundle savedinstancestate)

{

Super.oncreate (savedinstancestate);

Setcontentview (R.layout.main);

ImageView but= (ImageView) Findviewbyid (R.id.mainbutton);

Animation manimation = Animationutils.loadanimation (this, r.anim.alpha);

But.startanimation (manimation);

}

Method Two: Use the Paint class

Method: Change the alpha value of the graph by Paint.setalpha ();

public class Mainactivity extends Activity implements ontouchlistener{

Paint paint=new paint ();

Set initial alpha to 100 (opaque)

int al=100;

@Override

public void OnCreate (Bundle savedinstancestate) {

Super.oncreate (savedinstancestate);

Setcontentview (New Renderview (this));

}

Class Renderview extends View {

protected void OnDraw (canvas canvas) {

Get the screen length, width

int Height=canvas.getheight ();

int Width=canvas.getwidth ();

Draw a fully populated red rectangle and change the alpha value

Paint.setstyle (Paint.Style.STROKE);

Paint.setcolor (color.red);

Paint.setalpha (al--); Change the alpha (transparency) value

Canvas.drawrect (Width/2,2,width/3*2,height/2,paint);

Invalidate ();

}

}

}

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Several ways Android uses Alpha to achieve gradient effects