java - lambda 表达式中的返回类型错误 : Cannot be converted to boolean

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，指出 shapeType 无法转换为 boolean 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() 方法期望返回一个 boolean 值，现在您没有返回任何内容，请按如下方式更改您的 lambda。

giraffe.setOnTouchListener(
(view, motionEvent) -> {
    shapeType = ShapeType.GIRAFFE;
    return false;
});