使用 getDrawingCache 时是否有最大位图大小? [英] Is there a maximum bitmap size when using getDrawingCache?

问题描述

我正在尝试在 TextView 中创建文本的位图.过去，我使用 getDrawingCache 完成了此操作.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.

I'm trying to create a bitmap of the text in a TextView. In the past I have done this using getDrawingCache. However, now I have a need to create a bitmap of a TextView with much longer text than before. This is causing getDrawingCache to throw a NullPointerException.

虽然我说的是更长的文本"，但我并不是在说不合理的长.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.有解决方法吗?

Although I say "much longer text," I am not talking about unreasonably long. If I create a TextView that is 600 pixels wide at size 24 font, I get the exception at 53 lines of text (but not at 52 lines). Is there a workaround for this?

起初我想到了这个答案，其中布局在画布上绘制自己，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 宽度和高度在布局之前都是 0.我从来没有真正在屏幕上布置过我的 TextView.

At first I thought this answer, in which the layout draws itself on a canvas, was the solution. However, that didn't work for me because I am creating the TextView programmatically and the width and height are 0 before they get laid out. I never actually layout my TextView on screen.

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("
");
    }

    // 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

这不是 IllegalArgumentException 或 OutOfMemoryError(至少不是外部的，尽管这可能是内部的原因.)

Note

This is not an IllegalArgumentException or OutOfMemoryError (At least not externally, though maybe this is the reason internally.)

• Android 开发者控制台中的神秘堆栈跟踪(位图大小超过 32 位)
• 奇怪的将图像加载到位图对象时出现内存问题

推荐答案

您可以删除 buildDrawingCache 方法而只使用 canvas.由于您是以编程方式构建视图，因此您还需要在获取位图之前调用 measure() 和 layout().

You can drop the buildDrawingCache method and just use canvas. Since you are building the view programmatically you also need to call measure() and layout() before you can get a bitmap.

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("
");
    }

    // 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;
}

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