Is there a maximum bitmap size when using getDrawi

问题:

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.

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?

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.

Code for reference

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;
}

NullPointerException

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)
        ...

Note

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

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

回答1:

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.

The key lines are:

    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);

Here is the full example:

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;
}