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")

@Override

protected 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});