java如何只更改TextView的背景alpha而不是整个视图？

Question

N.B：这可能是一篇重复的文章。但之前没有一个解决方案对我有效

我正在尝试从RecyclerView适配器内部设置TextView（仅）背景不透明度（而不是textColor和background）。上一个问题的答案对我不起作用

先前建议的输出

Case 1:

holder.textView.setBackgroundColor(Color.argb(50, 0,255,0)); //this set alpha to whole view(both background + textColor).

Case 2:

holder.textView.setAlpha(50); //this also set alpha to whole view(both background + textColor).

Case 3:

holder.textView.getBackground().setAlpha(alpha); //NullPointerException

输出

java.lang.NullPointerException: Attempt to invoke virtual method 'void 安卓.graphics.drawable.Drawable.setAlpha(int)' on a null object reference

这是我的回收视图：

...
    @RequiresApi(api = Build.VERSION_CODES.O)
    @NonNull
    @Override
    public ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        TextView textView = new TextView(parent.getContext());
        return new ViewHolder(textView);
    }
    
    @Override
    public void onBindViewHolder(@NonNull ViewHolder holder, int position) {
        holder.textView.setAlpha(50);
    }

    static class ViewHolder extends RecyclerView.ViewHolder {
        private TextView textView;

        @RequiresApi(api = Build.VERSION_CODES.O)
        public ViewHolder(@NonNull View itemView) {
            super(itemView);
            this.textView = (TextView) itemView;
            LinearLayout.LayoutParams layoutParams = new LinearLayout.LayoutParams(LinearLayout.LayoutParams.MATCH_PARENT, LinearLayout.LayoutParams.WRAP_CONTENT);
            textView.setLayoutParams(layoutParams);
            textView.setTextAlignment(View.TEXT_ALIGNMENT_CENTER);
            textView.setPadding(4,4,4,4);
            textView.setAutoSizeTextTypeUniformWithConfiguration(6,24,1, TypedValue.COMPLEX_UNIT_DIP);
        }
    }

...

Answer 1

试试这个：

....
    @Override
    public void onBindViewHolder(@NonNull ViewHolder holder, int position) {
         ShapeDrawable drawable = new ShapeDrawable();
         drawable.getPaint().setColor(Color.GREEN); //Your color;
         drawable.getPaint().setAlpha(75); //BackGround Alpha between 0 to 100;
         holder.textView.setBackground(drawable);
    }