android - 调用 setText() 和 invalidate() 后，TextView 无法在 Canvas 上正确绘制

Question

我的目的是制作一个显示用户提供的文本的位图图像，该图像稍后可以保存到缓存中。

在调用 TextView.setText() 和 TextView.invalidate() 之后，TextView 没有像我预期的那样更新。它仍然在 Canvas 上绘制以前的文本。

@Override
public void onClick(View v) {
    // tv is a TextView and et is an EditText.
    tv.setText(et.getText().toString());
    tv.invalidate();
    // if measure() isn't called, getMeasuredWidth() returns previous value.tv.measure(0, 0);

    int screenWidth = (int) tv.getMeasuredWidth();
    int screenHeight = (int) tv.getMeasuredHeight();

    if (screenHeight * screenWidth != 0) {
        LinearLayout.LayoutParams layoutParams = new LinearLayout.LayoutParams(
                                                    screenWidth, screenHeight);
        Bitmap testB;

        testB = Bitmap.createBitmap(screenWidth, screenHeight, Bitmap.Config.ARGB_8888);
        Canvas c = new Canvas(testB);

        tv.draw(c);
        // tv draws previous String on Canvas c.

        iv = (ImageView) findViewById(R.id.image);
        iv.setLayoutParams(layoutParams);
        iv.setBackgroundColor(Color.RED);
        iv.setImageBitmap(testB);
    }
}

文件说

public void invalidate ()

Invalidate the whole view. If the view is visible, onDraw(android.graphics.Canvas) will be called at some point in the future. This must be called from a UI thread. To call from a non-UI thread, call postInvalidate().

这是否意味着我应该覆盖 onDraw() 方法？

Answer 1

我找到了解决方案...(可能是一个解决方案)

在调用draw()之前需要添加这一行:

tv.layout(0, 0, screenWidth, screenHeight);

我认为宽度和高度还没有更新，因为 getWidth() 返回以前的值。