android - 使用 getDrawingCache 时是否有最大位图大小？

Question

我正在尝试在 TextView 中创建文本的位图。过去，我使用 getDrawingCache 完成此操作。但是，现在我需要创建一个 TextView 的位图，其中的文本比以前长得多。这导致 getDrawingCache 抛出 NullPointerException。

虽然我说的是“更长的文本”，但我并不是在谈论不合理的长。如果我创建一个宽度为 600 像素、字体大小为 24 的 TextView，我会在 53 行文本(但不是 52 行)处得到异常。有解决办法吗？

起初我以为this answer ，其中布局将自身绘制在 canvas 上，这就是解决方案。但是，这对我不起作用，因为我正在以编程方式创建 TextView 并且 the width and height are 0在他们被布置之前。我从未真正在屏幕上布局我的 TextView。

引用代码

private Bitmap getBitmap(Context context){

    final int NUMBER_OF_LINES = 53; // 53 crashes, 52 doesn't
    final int width = 600; // width of TextView in pixels
    final int fontSize = 24;

    // create string with NUMBER_OF_LINES
    StringBuilder testString = new StringBuilder();
    for (int i = 0; i < NUMBER_OF_LINES; i++) {
        testString.append("\n");
    }

    // Create TextView
    TextView tvText = new TextView(context);
    LinearLayout.LayoutParams params = new LinearLayout.LayoutParams(
            LinearLayout.LayoutParams.WRAP_CONTENT,
            LinearLayout.LayoutParams.WRAP_CONTENT);
    tvText.setTextSize(fontSize);
    tvText.setWidth(width);
    tvText.setLayoutParams(params);
    tvText.setBackgroundColor(Color.WHITE); // even setting the background color affects crashing or not
    tvText.setText(testString);

    // Create bitmap
    tvText.setDrawingCacheEnabled(true);
    tvText.measure(View.MeasureSpec.makeMeasureSpec(0, View.MeasureSpec.UNSPECIFIED),
            View.MeasureSpec.makeMeasureSpec(0, View.MeasureSpec.UNSPECIFIED));
    tvText.layout(0, 0, tvText.getMeasuredWidth(), tvText.getMeasuredHeight());
    tvText.buildDrawingCache(true);
    Bitmap bitmap = Bitmap.createBitmap(tvText.getDrawingCache()); // crashes here
    tvText.setDrawingCacheEnabled(false);

    // This also didn't work because width and height are 0
    /*Bitmap bitmap = Bitmap.createBitmap(tvText.getWidth(), tvText.getHeight(),
            Bitmap.Config.ARGB_8888);
    Canvas canvas = new Canvas(bitmap);
    tvText.draw(canvas);*/

    return bitmap;
}

空指针异常

06-21 14:20:24.628    8036-8036/com.example.testsomecode E/AndroidRuntime﹕ FATAL EXCEPTION: main
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.testsomecode/com.example.testsomecode.MainActivity}: java.lang.NullPointerException
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2092)
        ...
 Caused by: java.lang.NullPointerException
        at android.graphics.Bitmap.createBitmap(Bitmap.java:494)
        at com.example.testsomecode.MainActivity.getBitmap(MainActivity.java:57) // -> Bitmap bitmap = Bitmap.createBitmap(tvText.getDrawingCache());
        at com.example.testsomecode.MainActivity.onCreate(MainActivity.java:25)
        ...

注意事项

这不是 IllegalArgumentException 或 OutOfMemoryError(至少在外部不是，尽管这可能是内部原因。)

• Mysterious stacktrace in Android developer console (bitmap size exceeds 32bits)
• Strange out of memory issue while loading an image to a Bitmap object

Answer 1

您可以删除 buildDrawingCache 方法，只使用 canvas。由于您是以编程方式构建 View ，因此在获取位图之前还需要调用 measure() 和 layout()。

关键行是:

    tvText.measure(View.MeasureSpec.makeMeasureSpec(0, View.MeasureSpec.UNSPECIFIED),
            View.MeasureSpec.makeMeasureSpec(0, View.MeasureSpec.UNSPECIFIED));
    tvText.layout(0, 0, tvText.getMeasuredWidth(), tvText.getMeasuredHeight());
    Bitmap bitmap = Bitmap.createBitmap(tvText.getWidth(), tvText.getHeight(),
            Bitmap.Config.ARGB_8888);
    Canvas canvas = new Canvas(bitmap);
    tvText.draw(canvas);

这里是完整的例子:

private Bitmap getBitmap(Context context){

    final int NUMBER_OF_LINES = 153;
    final int width = 600;
    final int fontSize = 24;

    // create string with NUMBER_OF_LINES
    StringBuilder testString = new StringBuilder();
    for (int i = 0; i < NUMBER_OF_LINES; i++) {
        testString.append("\n");
    }

    // Create TextView
    TextView tvText = new TextView(context);
    LinearLayout.LayoutParams params = new LinearLayout.LayoutParams(
            LinearLayout.LayoutParams.WRAP_CONTENT,
            LinearLayout.LayoutParams.WRAP_CONTENT);
    tvText.setTextSize(fontSize);
    tvText.setWidth(width);
    tvText.setLayoutParams(params);
    tvText.setBackgroundColor(Color.WHITE); // even setting the background color affects crashing or not
    tvText.setText(testString);
    tvText.measure(View.MeasureSpec.makeMeasureSpec(0, View.MeasureSpec.UNSPECIFIED),
            View.MeasureSpec.makeMeasureSpec(0, View.MeasureSpec.UNSPECIFIED));
    tvText.layout(0, 0, tvText.getMeasuredWidth(), tvText.getMeasuredHeight());


    // Create the bitmap from the view
    Bitmap bitmap = Bitmap.createBitmap(tvText.getWidth(), tvText.getHeight(),
            Bitmap.Config.ARGB_8888);
    Canvas canvas = new Canvas(bitmap);
    tvText.draw(canvas);

    return bitmap;
}