Android Canvas.DrawText
-
27-09-2019 - |
Pergunta
Eu tenho uma visão, estou desenhando com o objeto Canvas no método OnDraw (Canvas Canvas). Meu código é:
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);
O problema é que o texto não aparece através do fundo, o que estou fazendo de errado? Se eu remover o Canvas.drawpaint (tinta) e pintur.setColor (android.r.color.black), você poderá ver o texto na tela .....
Solução
Trabalhou isso, acontece que Android.R.Color.Black não é o mesmo que color.black. Alterou o código para:
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);
E tudo funciona bem agora !!
Outras dicas
Deve -se notar que o documentação recomenda usar um Layout
ao invés de Canvas.drawText
diretamente. Minha resposta completa sobre o uso de um StaticLayout
é aqui, mas vou fornecer um resumo abaixo.
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);
Aqui está um exemplo mais completo no contexto de uma visão personalizada:
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();
}
}