java - 从共享首选项中检索值时出错

Question

所以在一个 Activity 中，我试图将一个文件放入共享首选项中，然后在另一个 Activity 中，我试图烘烤该字符串，但由于某种原因，android 正在烘烤默认值而不是我从共享中输入的值偏好。

这是 MainActivity:

public void onPreviewFrame(byte[] data, Camera camera) {
        // By default preview data is in NV21 format, if needed it must be converted
        try {
            Camera.Size previewSize = camera.getParameters().getPreviewSize();
            int height = previewSize.height;
            int width = previewSize.width;

            ColorModelConverter converter = new ColorModelConverter(height, width);
            int[] pixels = converter.convert(data, this.colorFormat);

            int color = pickColor(pixels, height, width);
            updateColorData(color);

            storeColorInSharedPreferences(color);


            Log.i("FRAME PREVIEW", "Color updated");
        } catch (RuntimeException oops) {
            // Do nothing, exception is thrown because onPreviewFrame is called after camera is released
            Log.i("FRAME PREVIEW", "RuntimeException thrown into onPreviewFrame");
        }
    }

    public void storeColorInSharedPreferences(int color) {

        SharedPreferences sharedprefernces = getSharedPreferences("Mydata",Context.MODE_PRIVATE );
        SharedPreferences.Editor editor = sharedprefernces.edit();
        String first_control = String.valueOf(color);
        editor.putString("first_control", first_control);
        editor.commit();

这是第二个 Activity :

public class regressionlinecalculator extends ActionBarActivity {


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_regressionlinecalculator);
    }







    SharedPreferences sharedPreferences = getSharedPreferences("MyData",Context.MODE_PRIVATE);
    String first_control = sharedPreferences.getString("first_control", "");

    public void test(View view) {


        Toast display_final_value = Toast.makeText(getApplicationContext(), new String(first_control), Toast.LENGTH_SHORT);

        display_final_value.show();



    }
}

测试就是当我单击我在 xml 文件中定义的按钮时发生的情况。所以我的问题是，为什么 android 会一直保持默认值，即“”而不是颜色，这是我在其他 Activity 中输入到共享首选项中的值？

Answer 1

So my question is why does android keep toasting the default value, which is "" instead of color, the value which I inputted into shared preferences in the other activity?

这是因为您正在为 Toast 使用 getApplicationContext()。直接使用 Activity 的 Context。

Toast display_final_value = Toast.makeText(this,first_control, Toast.LENGTH_SHORT);

另一方面，您在检索 SharedPreference 对象时出现错字。使用常量来避免此类问题。此外，它的初始化应该移到回调方法中。例如。 onCreate

SharedPreferences sharedPreferences; 
String first_control;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_regressionlinecalculator);
    sharedPreferences = getSharedPreferences("Mydata",Context.MODE_PRIVATE); 
    first_control = sharedPreferences.getString("first_control", "");
}