我如何申请alpha渐变的图像上，这样它消失线？ 现在，我要创建单元宽度的矩形，并用它来绘制位图用油漆对象与α值在一个循环中被改变。我只是做了它，因为我想不出别的。因此，一个更合适的方法会更好。

 位图位= BitmapFactory.de codeStream（是）;
BMP位= Bitmap.createScaledBitmap（位图，100，151，TRUE））;
bitmap.recycle（）;

矩形Rect1的=新的Rect（0，0，100，100）;
矩形RECT2 =新的Rect（100，0，101，100）;

涂料粉刷=新的油漆（）;

canvas.drawBitmap（BMP，Rect1的，Rect1的，NULL）;
而（paint.getAlpha（）！= 0）{
    paint.setAlpha（paint.getAlpha（） -  5）;
    canvas.drawBitmap（BMP，RECT2，RECT2，油漆）;
    Rect2.set（Rect2.left + 1，Rect2.top，Rect2.right + 1，Rect2.bottom）;
}
 

像这样

P.S。我试图做到这一点的一个活的壁纸。

也许，所需的行为可能是只景色操作满足。 对于它，你应该：

RES /绘制/ gradient_shape.xml：

 ＆LT; XML版本=1.0编码=UTF-8＆GT？;
＆LT;形状的xmlns：机器人=htt​​p://schemas.android.com/apk/res/android＆GT;
    ＆LT;梯度
            机器人：startColor =＃00FFFFFF
            机器人：endColor =＃FFFFFFFF
            机器人：TYPE =线性/＆GT;
＆LT; /形状＆GT;
 

定义布局： activity_main.xml

 ＆LT; ImageView的
    机器人：ID =@ + ID /摄
    机器人：layout_width =match_parent
    机器人：layout_height =match_parent
    机器人：背景=@可绘制/摄
    机器人：SRC =@可绘制/ gradient_shape/＆GT;
 

在这里绘制/照片是刚刚的JPEG可绘制文件夹;

有的建议增加以下code的活性（它实际上取决于设备的本地配置，似乎是多余的了时下> 3.0的设备）：

 公共无效onAttachedToWindow（）{
     super.onAttachedToWindow（）;
     窗口窗口= getWindow（）;
     window.setFormat（PixelFormat.RGBA_8888）;
 }
 

在我所观察到的以下我4.1的设备：

它看起来像梯度。我仍然不知道这是否就是你要寻找的。

How can I apply an alpha gradient on an image so that it fades linearly? Right now, I'm creating rectangles of unit width and using it to draw the bitmap with a paint object with alpha value being changed in a loop. I only did it since I couldn't think of anything else. So a neater way would be better.

Bitmap bitmap = BitmapFactory.decodeStream(is);
Bitmap bmp = Bitmap.createScaledBitmap(bitmap, 100, 151, true));
bitmap.recycle();

Rect Rect1 = new Rect(0, 0, 100, 100);
Rect Rect2 = new Rect(100, 0, 101, 100);

Paint paint = new Paint();

canvas.drawBitmap(bmp, Rect1, Rect1, null);
while (paint.getAlpha() != 0) {
    paint.setAlpha(paint.getAlpha() - 5);
    canvas.drawBitmap(bmp, Rect2, Rect2, paint);
    Rect2.set(Rect2.left + 1, Rect2.top, Rect2.right + 1, Rect2.bottom);
}

Something like this

P.S. I'm trying to do this for a live wallpaper.

Probably, desired behaviour could be meet with only views manipulations. For it You should:

res/drawable/gradient_shape.xml:

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android">
    <gradient
            android:startColor="#00FFFFFF"
            android:endColor="#FFFFFFFF"
            android:type="linear" />
</shape>

Define layout: activity_main.xml:

<ImageView
    android:id="@+id/photo"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@drawable/photo"
    android:src="@drawable/gradient_shape" />

here drawable/photo is just jpeg in drawables folder;

Some suggests to add the following code to the activity (it, actually, depends on device native configuration and seems to be redundant for nowadays > 3.0 devices):

public void onAttachedToWindow() {
     super.onAttachedToWindow();
     Window window = getWindow();
     window.setFormat(PixelFormat.RGBA_8888);
 }

After that I've observed the following on my 4.1 device:

It looks like gradient. I'm still not sure if it's what You're looking for.