安卓透明文字 [英] Android transparent text
问题描述
我需要在渐变背景上显示一个 TextView
.TextView
本身应该有纯白色背景,并且文本应该是透明的.
I need to display a TextView
over a gradient background. The TextView
itself should have a plain white background, and the text should be transparent.
但是,为文本设置透明颜色(#00000000)不起作用:它只显示一个白色矩形,背景不显示文本所在的位置(文本与 TextView
背景).
However, setting a transparent color (#00000000) to the text doesn't work: it only shows a white rectangle, the background doesn't show up where the text is (the text takes the same color as the TextView
background).
如何在 TextView
上显示带有背景色的透明文本?
How can I display a transparent text with a background color on my TextView
?
推荐答案
2016 年 1 月 30 日更新
我做了一个小的库,并写了一个博文 不在此答案中,因此您无需复制和粘贴代码,我为您进行维护.:)
Update, Jan 30, 2016
I made a small library and written a blog post out of this answer, so you don't need to copy and paste code and I do the maintenance for you. :)
使用xml中的视图为:
Use the view in xml as:
<it.gilvegliach.android.transparenttexttextview.TransparentTextTextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:background="@drawable/view_bg"
android:text="Hello World" />
Gradle 依赖:
compile 'it.gilvegliach.android:transparent-text-textview:1.0.3'
<小时>
原答案
这是实现该效果的方法:
Original Answer
This is how you can achieve that effect:
- 在位图的透明背景上渲染文本
- 您使用该位图将文本形状从纯白色背景中裁剪出来
这是 TextView
的一个简单子类.
Here is a simple subclass of TextView
that does that.
final public class SeeThroughTextView extends TextView
{
Bitmap mMaskBitmap;
Canvas mMaskCanvas;
Paint mPaint;
Drawable mBackground;
Bitmap mBackgroundBitmap;
Canvas mBackgroundCanvas;
boolean mSetBoundsOnSizeAvailable = false;
public SeeThroughTextView(Context context)
{
super(context);
mPaint = new Paint();
mPaint.setXfermode(new PorterDuffXfermode(Mode.DST_OUT));
super.setTextColor(Color.BLACK);
super.setBackgroundDrawable(new ColorDrawable(Color.TRANSPARENT));
}
@Override
@Deprecated
public void setBackgroundDrawable(Drawable bg)
{
mBackground = bg;
int w = bg.getIntrinsicWidth();
int h = bg.getIntrinsicHeight();
// Drawable has no dimensions, retrieve View's dimensions
if (w == -1 || h == -1)
{
w = getWidth();
h = getHeight();
}
// Layout has not run
if (w == 0 || h == 0)
{
mSetBoundsOnSizeAvailable = true;
return;
}
mBackground.setBounds(0, 0, w, h);
invalidate();
}
@Override
public void setBackgroundColor(int color)
{
setBackgroundDrawable(new ColorDrawable(color));
}
@Override
protected void onSizeChanged(int w, int h, int oldw, int oldh)
{
super.onSizeChanged(w, h, oldw, oldh);
mBackgroundBitmap = Bitmap.createBitmap(w, h, Bitmap.Config.ARGB_8888);
mBackgroundCanvas = new Canvas(mBackgroundBitmap);
mMaskBitmap = Bitmap.createBitmap(w, h, Bitmap.Config.ARGB_8888);
mMaskCanvas = new Canvas(mMaskBitmap);
if (mSetBoundsOnSizeAvailable)
{
mBackground.setBounds(0, 0, w, h);
mSetBoundsOnSizeAvailable = false;
}
}
@Override
protected void onDraw(Canvas canvas)
{
// Draw background
mBackground.draw(mBackgroundCanvas);
// Draw mask
mMaskCanvas.drawColor(Color.BLACK, PorterDuff.Mode.CLEAR);
super.onDraw(mMaskCanvas);
mBackgroundCanvas.drawBitmap(mMaskBitmap, 0.f, 0.f, mPaint);
canvas.drawBitmap(mBackgroundBitmap, 0.f, 0.f, null);
}
}
示例截图:活动背景为靛蓝图案,TextView 背景为粉红色实心填充.
Example screenshot: indigo pattern for activity background, pink solid fill for TextView background.
这适用于纯色背景和一般可绘制对象.无论如何,这只是一个 BASIC 实现,不支持平铺等一些功能.
This works both for solid color backgrounds and general drawables. Anyway, this is only a BASIC implementation, some feature such as tiling are not supported.
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