是否有一个最大的位图大小使用getDrawingCache什么时候？ [英] Is there a maximum bitmap size when using getDrawingCache?

问题描述

我想创建一个的TextView 文本的位图。在过去，我已经做到了这一点使用 getDrawingCache 。不过，现在我有一个需要创建一个的TextView 的位图与更长的文本比以前。这是造成 getDrawingCache 来抛出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：要长得多的文字，我不是在谈论过长。如果我创建一个TextView是600像素宽的大小24的字体，我在53行文本（但不是在52线）得到的异常。是否有解决方法吗？

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?

起初我还以为这个答案，在这种布局绘制本身画布上，是解决办法。但是，这并没有为我工作，因为我编程方式创建的TextView和的宽度和高度都为0 他们得到奠定之前。我从来没有真正的布局我的的TextView 在屏幕上。

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("\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

这是不是一个IllegalArgumentException或OutOfMemoryError异常（至少不是外部，但也许这是内部的原因。）

Note

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

• <一个href="http://stackoverflow.com/questions/9370145/mysterious-stacktrace-in-android-developer-console-bitmap-size-exceeds-32bits">Mysterious堆栈跟踪在Android开发者控制台（位图的大小超过32位）
• <一个href="http://stackoverflow.com/questions/477572/strange-out-of-memory-issue-while-loading-an-image-to-a-bitmap-object">Strange内存不足的问题，同时加载图像为位图对象

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

推荐答案

您可以删除 buildDrawingCache 的方法，只是使用画布。既然你正在构建的视图编程，你还需要调用措施（）和布局（）之前，你可以得到一个位图。

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.

关键线路有：

    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);

下面是完整的例子：

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;
}

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