python - saveFrame 产生 NullPointerException 错误

Question

我对处理还是新手，并且正在使用 Python，但编译器似乎会产生 NullPointerException 错误。如何解决这个问题？

如果有帮助，我正在使用 Windows。

这是原始程序代码-

def setup():
    size(400, 400)
    stroke(255)

def draw():
    line(150, 25, mouseX, mouseY)

def mousePressed():
    background(192, 64, 0)

saveFrame("output.png") 

processing.app.SketchException: java.lang.NullPointerException
    at processing.core.PApplet.saveFrame(PApplet.java:3984)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at org.python.core.PyReflectedFunction.__call__(PyReflectedFunction.java:188)
    at org.python.core.PyReflectedFunction.__call__(PyReflectedFunction.java:206)
    at org.python.core.PyObject.__call__(PyObject.java:497)
    at org.python.core.PyObject.__call__(PyObject.java:501)
    at org.python.core.PyMethod.__call__(PyMethod.java:141)
    at org.python.pycode._pyx387.f$0(sketch_190727c.pyde:1)
    at org.python.pycode._pyx387.call_function(sketch_190727c.pyde)
    at org.python.core.PyTableCode.call(PyTableCode.java:171)
    at org.python.core.PyCode.call(PyCode.java:18)
    at org.python.core.Py.runCode(Py.java:1614)
    at org.python.core.Py.exec(Py.java:1658)
    at org.python.pycode._pyx386.f$0(C:/Users/Abi/AppData/Local/Temp/sketch_190727c1462189324264258430/sketch_190727c.pyde:96)
    at org.python.pycode._pyx386.call_function(C:/Users/Abi/AppData/Local/Temp/sketch_190727c1462189324264258430/sketch_190727c.pyde)
    at org.python.core.PyTableCode.call(PyTableCode.java:171)
    at org.python.core.PyCode.call(PyCode.java:18)
    at org.python.core.Py.runCode(Py.java:1614)
    at org.python.core.Py.exec(Py.java:1658)
    at org.python.util.PythonInterpreter.exec(PythonInterpreter.java:276)
    at jycessing.PAppletJythonDriver.processSketch(PAppletJythonDriver.java:230)
    at jycessing.PAppletJythonDriver.findSketchMethods(PAppletJythonDriver.java:590)
    at jycessing.Runner.runSketchBlocking(Runner.java:398)
    at jycessing.mode.run.SketchRunner.lambda$2(SketchRunner.java:112)
    at java.lang.Thread.run(Thread.java:748)

    at jycessing.mode.run.SketchRunner.convertPythonSketchError(SketchRunner.java:224)
    at jycessing.mode.run.SketchRunner.lambda$2(SketchRunner.java:119)
    at java.lang.Thread.run(Thread.java:748)
```

Answer 1

考虑一下 saveFrame() 函数何时被调用。

您已将对 saveFrame() 的调用置于与 setup()、draw() 声明相同的级别和 mousePressed() 函数。这意味着您在调用其他函数之前调用saveFrame()。这就是导致 NullPointerException 的原因。

要解决此问题，您可能需要移动 saveFrame() 调用，使其位于 mousePressed() 函数内。

顺便说一句，这是一个运行时错误，而不是编译器错误。