我有一个视图,我正在使用 onDraw(Canvas canvas) 方法中的 Canvas 对象进行绘制。我的代码是:
Paint paint = new Paint();
paint.setColor(Color.WHITE);
paint.setStyle(Style.FILL);
canvas.drawPaint(paint);
paint.setColor(android.R.color.black);
paint.setTextSize(20);
canvas.drawText("Some Text", 10, 25, paint);
问题是文本没有通过背景显示,我做错了什么?如果我删除 canvas.drawPaint(paint) 和 paint.setColor(android.R.color.black) 你可以在屏幕上看到文字.....
解决了这个问题,结果发现 android.R.color.black 与 Color.BLACK 不同。将代码更改为:
Paint paint = new Paint();
paint.setColor(Color.WHITE);
paint.setStyle(Style.FILL);
canvas.drawPaint(paint);
paint.setColor(Color.BLACK);
paint.setTextSize(20);
canvas.drawText("Some Text", 10, 25, paint);
现在一切正常!
应该注意的是,documentation 建议使用 Layout
而不是直接使用 Canvas.drawText
。我关于使用 StaticLayout
的完整答案是 here,但我将在下面提供一个摘要。
String text = "This is some text.";
TextPaint textPaint = new TextPaint();
textPaint.setAntiAlias(true);
textPaint.setTextSize(16 * getResources().getDisplayMetrics().density);
textPaint.setColor(0xFF000000);
int width = (int) textPaint.measureText(text);
StaticLayout staticLayout = new StaticLayout(text, textPaint, (int) width, Layout.Alignment.ALIGN_NORMAL, 1.0f, 0, false);
staticLayout.draw(canvas);
这是自定义视图上下文中的更完整示例:
https://i.stack.imgur.com/ZrrTu.png
public class MyView extends View {
String mText = "This is some text.";
TextPaint mTextPaint;
StaticLayout mStaticLayout;
// use this constructor if creating MyView programmatically
public MyView(Context context) {
super(context);
initLabelView();
}
// this constructor is used when created from xml
public MyView(Context context, AttributeSet attrs) {
super(context, attrs);
initLabelView();
}
private void initLabelView() {
mTextPaint = new TextPaint();
mTextPaint.setAntiAlias(true);
mTextPaint.setTextSize(16 * getResources().getDisplayMetrics().density);
mTextPaint.setColor(0xFF000000);
// default to a single line of text
int width = (int) mTextPaint.measureText(mText);
mStaticLayout = new StaticLayout(mText, mTextPaint, (int) width, Layout.Alignment.ALIGN_NORMAL, 1.0f, 0, false);
// New API alternate
//
// StaticLayout.Builder builder = StaticLayout.Builder.obtain(mText, 0, mText.length(), mTextPaint, width)
// .setAlignment(Layout.Alignment.ALIGN_NORMAL)
// .setLineSpacing(1, 0) // multiplier, add
// .setIncludePad(false);
// mStaticLayout = builder.build();
}
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
// Tell the parent layout how big this view would like to be
// but still respect any requirements (measure specs) that are passed down.
// determine the width
int width;
int widthMode = MeasureSpec.getMode(widthMeasureSpec);
int widthRequirement = MeasureSpec.getSize(widthMeasureSpec);
if (widthMode == MeasureSpec.EXACTLY) {
width = widthRequirement;
} else {
width = mStaticLayout.getWidth() + getPaddingLeft() + getPaddingRight();
if (widthMode == MeasureSpec.AT_MOST) {
if (width > widthRequirement) {
width = widthRequirement;
// too long for a single line so relayout as multiline
mStaticLayout = new StaticLayout(mText, mTextPaint, width, Layout.Alignment.ALIGN_NORMAL, 1.0f, 0, false);
}
}
}
// determine the height
int height;
int heightMode = MeasureSpec.getMode(heightMeasureSpec);
int heightRequirement = MeasureSpec.getSize(heightMeasureSpec);
if (heightMode == MeasureSpec.EXACTLY) {
height = heightRequirement;
} else {
height = mStaticLayout.getHeight() + getPaddingTop() + getPaddingBottom();
if (heightMode == MeasureSpec.AT_MOST) {
height = Math.min(height, heightRequirement);
}
}
// Required call: set width and height
setMeasuredDimension(width, height);
}
@Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
// do as little as possible inside onDraw to improve performance
// draw the text on the canvas after adjusting for padding
canvas.save();
canvas.translate(getPaddingLeft(), getPaddingTop());
mStaticLayout.draw(canvas);
canvas.restore();
}
}
R.color.black
的res/colors.xml
文件中的颜色定义,则不能只使用 ID。如果要从资源中获取实际颜色值,请使用paint.setColor(getResources().getColor(R.color.black));
dp
中设置文本大小,您可以用作 this