Android：GradientDrawable只是绘制黑色

Question

I have a an app with several sliders with and the purpose is to change the color of a set of LED lights i have connected to it. I am implementing a UI with a function which will change the color of a radial gradient to give an approximation of the LED color.

I can define the default background like this:

<shape xmlns:android="http://schemas.android.com/apk/res/android"
android:shape="rectangle" >

<gradient
    android:id="@+id/radGrad"
    android:centerColor="#ecd473"
    android:centerY="0%"
    android:centerX="0%"
    android:endColor="#000000"
    android:gradientRadius="600"
    android:innerRadiusRatio="2"
    android:startColor="#f9f7a8"
    android:type="radial" >
</gradient>
</shape>

and in my activity layout:

This will be displayed as a background which looks like this: enter image description here

I am attempting to overwrite the background with values that are selected by the sliders in the picture. I want to essentially create the same background image with a radial gradient in the top left corner with various colors, but i am stuck.

Here is my java code, after OnCreate()

View backgroundView;
GradientDrawable background;
background = this.getWindow().getDecorView();

and the rest of the code when i select the submit button:

submitButton.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            color = new int[3];
            color[0]=0xecd473; //these values will eventually be changed by the slider
            color[1]=0xf9f7a8;
            color[2]=0xffffff;
            background = new GradientDrawable(GradientDrawable.Orientation.BL_TR, color);
            background.mutate();
            background.setGradientType(GradientDrawable.RADIAL_GRADIENT);
            background.setGradientRadius(600);
            background.setGradientCenter(0,0);
            background.setShape(GradientDrawable.RECTANGLE);
            background.setCornerRadius(50f);
            background.setColors(color);
            backgroundView.setBackground(background);
            progressTextView.setText("Hue: " + hueValue + " Brightness: " + brightValue + " Saturation: " + satValue);
        }
    });

}    

No matter what colors i feed background.setColors(color) the background appears black after I click the submit. I feel like I am missing something important and other examples have not helped. I hope this is clear.

Answer 1

I figured it out. The color values were missing their Alpha values so I am guessing it was transparent or the function was not taking it. By adding ff to each color value the background came into focus.

Answer 2

First off, you dont need to use backdround.mutate(); the object is already mutable. Also the function .setColor() requires an argb value. Although the documentation says that it also accepts an rgb, it translates an argb value without an an alpha as 100% transparency, which might as well be invisible. You need to add the alpha when you are passing the value. That is why you need an extra FF to prepend your rgb.