Android:传递活动类时的“表达式期望”

Question

我是Android编程和Java的新手，我不知道是什么导致了这个错误；据我所知，这应该是可行的。在下面所示的代码中(第一个片段的末尾)，"ColourOutput.do_output((Activity) com.(name-removed).(app-name-removed).ColourActivity);"行在AndroidStudio1.1.0中的文本"com.(name-removed).(app-name-removed).ColourActivity"上给出了错误"Expression expected"。

(这是在类"public class ColourActivity extends Activity"中。)

        private Camera.PreviewCallback preview_callback = new Camera.PreviewCallback() {
        @Override
        public void onPreviewFrame(byte[] data, Camera camera) {
            int width = mCamera.getParameters().getPreviewSize().width;
            int height = mCamera.getParameters().getPreviewSize().height;
            int raw_pixels[];
            int pixels[];

            raw_pixels = new int[width * height];
            pixels = new int[get_sample_width() * get_sample_height()];
            convert_yuv(raw_pixels, data, width, height);
            crop_pixels(raw_pixels, pixels, width, height, (width - get_sample_width()) / 2, (height - get_sample_height()) / 2, get_sample_width(), get_sample_height());

            if (PreferenceManager.getDefaultSharedPreferences(getApplicationContext()).getBoolean("use_mean", true) == true) {
                ColourOutput.add_colour_to_output(
                        ColourTools.get_mean(
                                pixels, get_sample_width(), get_sample_height(),
                                PreferenceManager.getDefaultSharedPreferences(getApplicationContext()).getBoolean("detect_secondary", true),
                                PreferenceManager.getDefaultSharedPreferences(getApplicationContext()).getBoolean("detect_white", true),
                                PreferenceManager.getDefaultSharedPreferences(getApplicationContext()).getBoolean("detect_brightness", true),
                                PreferenceManager.getDefaultSharedPreferences(getApplicationContext()).getInt("quantization_secondary", 32),
                                PreferenceManager.getDefaultSharedPreferences(getApplicationContext()).getInt("quantization_dark", 43),
                                PreferenceManager.getDefaultSharedPreferences(getApplicationContext()).getInt("quantization_light", 128),
                                PreferenceManager.getDefaultSharedPreferences(getApplicationContext()).getBoolean("quantization_matching_only", true)
                        ),
                        ColourOutput.ColourType.MEAN);
            }
            if (PreferenceManager.getDefaultSharedPreferences(getApplicationContext()).getBoolean("use_mode", true) == true) {
                ColourOutput.add_colour_to_output(
                        ColourTools.get_mode(
                                pixels, get_sample_width(), get_sample_height(),
                                PreferenceManager.getDefaultSharedPreferences(getApplicationContext()).getBoolean("detect_secondary", true),
                                PreferenceManager.getDefaultSharedPreferences(getApplicationContext()).getBoolean("detect_white", true),
                                PreferenceManager.getDefaultSharedPreferences(getApplicationContext()).getBoolean("detect_brightness", true),
                                PreferenceManager.getDefaultSharedPreferences(getApplicationContext()).getInt("quantization_secondary", 32),
                                PreferenceManager.getDefaultSharedPreferences(getApplicationContext()).getInt("quantization_dark", 43),
                                PreferenceManager.getDefaultSharedPreferences(getApplicationContext()).getInt("quantization_light", 128),
                                PreferenceManager.getDefaultSharedPreferences(getApplicationContext()).getBoolean("quantization_matching_only", true)
                        ),
                        ColourOutput.ColourType.MODE);
            }
            ColourOutput.do_output((Activity) com.(name-removed).(app-name-removed).ColourActivity);
        }
    };

以下是"ColourOutput.do_output"的定义

public class ColourOutput {
    private static boolean output_clear = true;
    private static String output_buffer = "";

    public static enum ColourType {
        MEAN,
        MODE
    }

    public static void add_colour_to_output(ColourTools.ColourDescription colour, ColourType type) {
        if (output_clear == true) {
            output_buffer = colour.Brightness.toString() + " " + colour.Colour.toString();
        }
        else {
            output_buffer = output_buffer + " " + colour.Brightness.toString() + " " + colour.Colour.toString();
        }
        output_clear = false;
    }

    public static void do_output(Activity activity) {
        ((TextView) activity.findViewById(R.id.output_text)).setText(output_buffer);
        output_buffer = "";
        output_clear = true;
    }
}

Answer 1

错误消息应该是不言自明的：...ColourActivity是一个类名，而一个类名本身并不是一个有效的表达式。这不是android问题，这是一个简单的语法错误。

do_output()需要一个Activity的实例。我不太清楚，你在哪里试图通过传递活动类的名字来达到什么目的。

我想，既然您是在活动中调用do_output()，那么您可以尝试一下

ColourOutput.do_output(ColorActivity.this);

而不是。

正如@Priya所建议的那样，明确引用ColorActivity.this是必要的，因为您从内部类中调用方法，而this引用该内部类的实例。