如何在TextView颜色上设置带有角度的渐变？

Question

以下代码将在textview（不是背景，而是文本本身）上设置渐变。但是我需要更改此渐变的角度，该怎么做？

Shader textShader = new LinearGradient(0, 0, 0, textView.getPaint().getTextSize(),
        new int[]{context.getResources().getColor(R.color.color1), context.getResources().getColor(R.color.color2)},
        new float[]{0, 1}, Shader.TileMode.CLAMP);
textView.getPaint().setShader(textShader);

先谢谢您。

Answer 1

final TextView myTextView = findViewById(R.id.my_text_view);

myTextView.post(new Runnable() 
    {

         @Override

            public void run() {

                int length = textView.getMeasuredWidth();

            float angle = 45; // specify angle in degrees here

            Shader textShader = new LinearGradient(0, 0, (int) (Math.sin(Math.PI * angle / 180) * length), 
                                    (int) (Math.cos(Math.PI * angle / 180) * length),

                                        new int[]{Color.BLUE, Color.GREEN, Color.GREEN, Color.BLUE, Color.RED, Color.GREEN, Color.BLUE, Color.RED},

    null, 
        Shader.TileMode.CLAMP);

        myTextView.getPaint().setShader(textShader);

            textView.invalidate();

            }

    });

Answer 2

据此answer，我修改了您的代码。试试这个：

double angleInRadians = Math.toRadians(45);
double length = textView.getPaint().getTextSize();

double endX = Math.sin(angleInRadians) * length;
double endY = Math.cos(angleInRadians) * length;

Shader textShader = new LinearGradient(0, 0, endX, endY,
        new int[]{context.getResources().getColor(R.color.color1), context.getResources().getColor(R.color.color2)},
        new float[]{0, 1}, Shader.TileMode.CLAMP);
textView.getPaint().setShader(textShader);

更新：我很to愧地说我的以上答案不正确。这些答案（mayank1513 answer和Chaudhari Sachin answer）相同，虽然很好，但几乎没有错误：1.对于超过90度的后肢，它们无法正常工作。例如，如果您以180度对其进行测试，那么您将看不到任何渐变，因为这些解决方案使用（0,0）点作为旋转中心。2.如果您的TextView的宽度或高度大于或小于其文本宽度或高度，则渐变无法正确呈现。例如，您可以通过具有match_parent宽度和高度，居中Hello文本的TextView或启用的滚动小TextView和长文本的滚动测试。我开发了新的解决方案。它首先计算文本边界，然后围绕此边界的中心旋转渐变线。

textView.post(new Runnable() {
    @Override
    public void run() {

        final Rect textBound = new Rect(Integer.MAX_VALUE, Integer.MAX_VALUE, Integer.MIN_VALUE, Integer.MIN_VALUE);

        final Layout layout = textView.getLayout();
        for(int i = 0; i < textView.getLineCount(); i++) {
            float left = layout.getLineLeft(i);
            float right = layout.getLineRight(i);
            if(left < textBound.left) textBound.left = (int)left;
            if(right > textBound.right) textBound.right = (int)right;
        }
        textBound.top = layout.getLineTop(0);
        textBound.bottom = layout.getLineBottom(textView.getLineCount() - 1);
        if(textView.getIncludeFontPadding()) {
            Paint.FontMetrics fontMetrics = textView.getPaint().getFontMetrics();
            textBound.top += (fontMetrics.ascent - fontMetrics.top);
            textBound.bottom -= (fontMetrics.bottom - fontMetrics.descent);
        }

        double angleInRadians = Math.toRadians(45);

        double r = Math.sqrt(Math.pow(textBound.bottom - textBound.top, 2) +
                Math.pow(textBound.right - textBound.left, 2)) / 2;

        float centerX = textBound.left + (textBound.right - textBound.left) / 2;
        float centerY = textBound.top + (textBound.bottom - textBound.top) / 2;

        float startX = (float)Math.max(textBound.left, Math.min(textBound.right, centerX - r * Math.cos(angleInRadians)));
        float startY = (float)Math.min(textBound.bottom, Math.max(textBound.top, centerY - r * Math.sin(angleInRadians)));

        float endX = (float)Math.max(textBound.left, Math.min(textBound.right, centerX + r * Math.cos(angleInRadians)));
        float endY = (float)Math.min(textBound.bottom, Math.max(textBound.top, centerY + r * Math.sin(angleInRadians)));

        Shader textShader = new LinearGradient(startX, startY, endX, endY,
                new int[]{context.getResources().getColor(R.color.color1),
                        context.getResources().getColor(R.color.color2)},
                new float[]{0, 1}, Shader.TileMode.CLAMP);

        textView.setTextColor(Color.WHITE);
        textView.getPaint().setShader(textShader);
    }
});

Answer 3

工作代码

final double angleInRadians = Math.toRadians(45);
final TextView textView = findViewById(R.id.app_name);
    textView.post(new Runnable() {
        @Override
        public void run() {
            double length = textView.getMeasuredWidth();

            double endX = Math.sin(angleInRadians) * length;
            double endY = Math.cos(angleInRadians) * length;

            Shader textShader = new LinearGradient(0, 0, (int) endX, (int) endY,
                    new int[]{Color.BLUE, Color.GREEN, Color.GREEN, Color.BLUE, Color.RED, Color.GREEN, Color.BLUE, Color.RED},
                    null, Shader.TileMode.CLAMP);
            textView.getPaint().setShader(textShader);
            textView.invalidate();
        }
    });

这将以指定角度设置渐变。