java - 你如何获得按钮的背景颜色？

Question

你如何获得按钮的背景颜色？我尝试了以下方法:

 public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Button btn1 = findViewById(R.id.button);
        btn1.setBackgroundColor(getResources().getColor(R.color.red));
        //color red is added to colors.xml <color name="red">#FF0000</color>

        btn1.setOnClickListener(v -> {

          ColorDrawable btnColor = (ColorDrawable) btn1.getBackground();

          int clr = btnColor.getColor();

          if (clr == getResources().getColor(R.color.red)) {
              String line = "it's red";
              btn1.setText(line);
            }
        });
    }
}

当我单击按钮时，应用程序关闭，我得到了这个

 java.lang.ClassCastException: android.graphics.drawable.RippleDrawable cannot be cast to android.graphics.drawable.ColorDrawable

谁能解释我做错了什么？

Answer 1

由于您使用的是 MaterialComponents主题你的Button在运行时被 MaterialButton 替换.
使用 setBackgroundTintList 而不是 setBackgroundColor并使用 getBackgroundTintList() 检索 ColorStateList .
就像是:

    MaterialButton button = findViewById(R.id.button);
    button.setBackgroundTintList(ColorStateList.valueOf(ContextCompat.getColor(this, R.color.red600)));
    ColorStateList colorStateList = button.getBackgroundTintList();

    int defaultColor = colorStateList.getColorForState(
            new int[] { android.R.attr.state_enabled},0);