lambda 表达式中的错误返回类型：无法转换为布尔值

Question

我需要通过触摸按钮来更改 shapeType。我尝试了这种方法，但出现错误，提示 shapeType 无法转换为布尔值。代码：public class MainActivity extends AppCompatActivity {private ArFragment arFragment;private enum ShapeType {    GIRAFFE,    HIPPO,    ELEPHANT}private ShapeType shapeType = ShapeType.GIRAFFE;@SuppressLint("ClickableViewAccessibility")@Overrideprotected void onCreate(Bundle savedInstanceState) {    super.onCreate(savedInstanceState);    setContentView(R.layout.activity_main);    arFragment = (ArFragment) getSupportFragmentManager().findFragmentById(R.id.fragment);    Button giraffe = findViewById(R.id.giraffebutt);    Button hippo = findViewById(R.id.hippobutt);    Button elephant = findViewById(R.id.elephantbutt);    giraffe.setOnTouchListener(view -> shapeType = ShapeType.GIRAFFE);    hippo.setOnTouchListener(view ->shapeType = ShapeType.HIPPO);    elephant.setOnTouchListener(view ->shapeType = ShapeType.ELEPHANT);  }}错误：Bad return type in lambda expression: ShapeType cannot be converted to boolean

Answer 1

您的onTouch()方法现在期望返回一个布尔值，您没有返回任何东西，如下更改您的 lambda。

giraffe.setOnTouchListener(

(view, motionEvent) -> {

    shapeType = ShapeType.GIRAFFE;

    return false;

});

Answer 2

ButtonsetOnTouchListener提供一个Viewand MotionEvent，并期望一个boolean返回类型。

giraffe.setOnTouchListener((view, event) -> {

    shapeType = ShapeType.GIRAFFE);

    return true; // return true if event is consumed, false otherwise

});