Question

我正在尝试开发一个Q＆amp; A应用程序，它有一个活动和多个类，可以改变文本视图，按钮，分数等。我有一个setter和getter类。我的主要活动包含一个名为set的方法，它将每个文本视图，按钮分配给它们相应的ID。当我尝试调用main.set（）;我收到错误：

java.lang.NullPointerException: Attempt to invoke virtual method
'android.view.View android.view.Window.findViewById(int)' on a null object
reference

如果我将set（）方法复制并粘贴到我的MorseFalls类中并在该类中调用set（），我就不会收到错误。这让我相信方法和变量不会传递到其他类。有人可以帮忙吗？我已经被困在这5天以上了，它正在破坏我的头脑。我将为调用set方法的main和类粘贴我的代码：

public class MainActivity extends AppCompatActivity {


public static Model model = new Model();

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);
    set();
    beginMorse();
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.menu_main, menu);
    return true;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // Handle action bar item clicks here. The action bar will
    // automatically handle clicks on the Home/Up button, so long
    // as you specify a parent activity in AndroidManifest.xml.
    int id = item.getItemId();

    //noinspection SimplifiableIfStatement
    if (id == R.id.action_settings) {
        return true;
    }

    return super.onOptionsItemSelected(item);
}



//Which scale to go to next (if true means selected)
public void scale(){
    //not relevant
}

//Morse Falls
public void beginMorse() {
    // Start intent here
    Intent intent = new Intent(this, MorseFalls.class);
    intent.putExtra("intVariableName", 0);
    startActivity(intent);
}


public void set(){
    model.setT((TextView) findViewById(R.id.Question));
    model.setA((TextView) findViewById(R.id.AnswerA));
    model.setB((TextView) findViewById(R.id.AnswerB));
    model.setC((TextView) findViewById(R.id.AnswerC));
    model.setD((TextView) findViewById(R.id.AnswerD));
    model.setCs((TextView) findViewById(R.id.currentscore));
    model.setScore((TextView) findViewById(R.id.Score));
    model.setUnticked((TextView) findViewById(R.id.please_answer));
    model.setCC((TextView) findViewById(R.id.Answer2C));
    model.setDD((TextView) findViewById(R.id.Answer2D));
    model.setE((TextView) findViewById(R.id.AnswerE));
    model.setF((TextView) findViewById(R.id.AnswerF));
    model.setG((TextView) findViewById(R.id.AnswerG));
    model.setH((TextView) findViewById(R.id.AnswerH));
    model.setMyVib((Vibrator) this.getSystemService(VIBRATOR_SERVICE));
    model.setB((Button) findViewById(R.id.button));
    model.setNext_test((Button) findViewById(R.id.Next_Test));
    model.setR((RadioGroup) findViewById(R.id.radioGroup));;
    model.setOldpatient((Button) findViewById(R.id.oldtest));
    model.setNewpatient((Button) findViewById(R.id.newtest));
}

}

/**
 * Morse Falls scale
 */
public class MorseFalls extends AppCompatActivity{



private Model model = MainActivity.model;
private MainActivity main = new MainActivity();

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);

    //passing intent
    Intent mIntent = getIntent();

    //ERROR LIES HERE
    main.set();
    //set();
    declaration();

    model.getCC().setVisibility(View.GONE);
    model.getDD().setVisibility(View.GONE);
    findViewById(R.id.button).setVisibility(View.VISIBLE);

    //Morse Falls question one
    questionOne();
    PreviousScore = score;
    //button listener, when button clicked, produce output on textfield "Score"
    model.getButton().setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            model.getMyVib().vibrate(70);
            PreviousScore = score;

            //Score.setText(String.valueOf(action()));
            model.getScore().setText(String.valueOf(score));
            model.getCs().setText(String.valueOf(score));
            i++;

            //If answer not selected display "Please select answer
            if (model.getR().getCheckedRadioButtonId() == -1) {
                model.getUnticked().setVisibility(View.VISIBLE);
                model.getUnticked().setText("Please Select An Answer");
            } else {
                //Loop through questions
                if (i == 1)
                    questionOne();
                if (i == 2)
                    questionTwo();
                if (i == 3)
                    questionThree();
                if (i == 4)
                    questionFour();
                if (i == 5)
                    questionFive();
                if (i == 6)
                    questionSix();
                if (i == 7)
                    MorseFinish();
            }

            //For testing purpose keep displaying score after each answer
            model.getR().clearCheck();
            model.getCs().setText("Current Score: " + String.valueOf(score));

        }

    });

    //set Morse to false then call scalr question which shows which scale to complete next
    model.getNext_test().setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            model.getMyVib().vibrate(70);
            main.Morse = false;
            main.scale();
        }

    });

}


@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.menu_main, menu);
    return true;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // Handle action bar item clicks here. The action bar will
    // automatically handle clicks on the Home/Up button, so long
    // as you specify a parent activity in AndroidManifest.xml.
    int id = item.getItemId();

    //noinspection SimplifiableIfStatement
    if (id == R.id.action_settings) {
        return true;
    }

    return super.onOptionsItemSelected(item);
}

//declaring buttons visible and their text
private void declaration(){
    //not relevant
}


//scoring system
public void onRadioButtonClicked(View view) {
    //not relevant
        }
}

/*
Questions
 */
private void questionOne(){
    //not relevant
}

private void questionTwo(){
    //not relevant
}

private void questionThree(){
    //not relevant
}

private void questionFour(){
    //not relevant
}

private void questionFive(){
    //not relevant
}

private void questionSix(){
    //not relevant
}

//Display Morse Score and show advance button
private void MorseFinish(){
    model.getA().setVisibility(View.GONE);
    model.getB().setVisibility(View.GONE);
    model.getT().setText("Final Morse Score");
    model.getNext_test().setVisibility(View.VISIBLE);
    model.getScore().setVisibility(View.VISIBLE);
    model.getButton().setVisibility(View.VISIBLE);

}


public void set(){
    model.setT((TextView) findViewById(R.id.Question));
    model.setA((TextView) findViewById(R.id.AnswerA));
    model.setB((TextView) findViewById(R.id.AnswerB));
    model.setC((TextView) findViewById(R.id.AnswerC));
    model.setD((TextView) findViewById(R.id.AnswerD));
    model.setCs((TextView) findViewById(R.id.currentscore));
    model.setScore((TextView) findViewById(R.id.Score));
    model.setUnticked((TextView) findViewById(R.id.please_answer));
    model.setCC((TextView) findViewById(R.id.Answer2C));
    model.setDD((TextView) findViewById(R.id.Answer2D));
    model.setE((TextView) findViewById(R.id.AnswerE));
    model.setF((TextView) findViewById(R.id.AnswerF));
    model.setG((TextView) findViewById(R.id.AnswerG));
    model.setH((TextView) findViewById(R.id.AnswerH));
    model.setMyVib((Vibrator) this.getSystemService(VIBRATOR_SERVICE));
    //model.setB((Button) findViewById(R.id.button));
    model.setNext_test((Button) findViewById(R.id.Next_Test));
    model.setR((RadioGroup) findViewById(R.id.radioGroup));
    model.setCheckTinetti((CheckBox) findViewById(R.id.checkTinetti));
    model.setCheckEfficacy((CheckBox) findViewById(R.id.checkEfficacy));
    model.setCheckFRAT((CheckBox) findViewById(R.id.checkFRAT));
    model.setCheckMorse((CheckBox) findViewById(R.id.checkMorse));
    model.setOldpatient((Button) findViewById(R.id.oldtest));
    model.setNewpatient((Button) findViewById(R.id.newtest));
    model.setButton((Button) findViewById(R.id.button));
}

}

型号：

/**
 * Created by user on 07/03/2016.
 */
public class Model extends AppCompatActivity {

public static Vibrator myVib;
public static TextView T, A, B, C, D, E, F, G, H, CC, DD, cs, score, unticked;
public static Button next_test, button, newpatient, oldpatient;
public static RadioGroup r;
public static CheckBox checkTinetti, checkEfficacy, checkFRAT, checkMorse;

public static Vibrator getMyVib() {
    return myVib;
}

public static void setMyVib(Vibrator myVib) {
    Model.myVib = myVib;
}

public static TextView getT() {
    return T;
}

public static void setT(TextView t) {
    T = t;
}

public static TextView getA() {
    return A;
}

public static void setA(TextView a) {
    A = a;
}

public static TextView getB() {
    return B;
}

public static void setB(TextView b) {
    B = b;
}

public static TextView getC() {
    return C;
}

public static void setC(TextView c) {
    C = c;
}

public static TextView getD() {
    return D;
}

public static void setD(TextView d) {
    D = d;
}

public static TextView getE() {
    return E;
}

public static void setE(TextView e) {
    E = e;
}

public static TextView getF() {
    return F;
}

public static void setF(TextView f) {
    F = f;
}

public static TextView getG() {
    return G;
}

public static void setG(TextView g) {
    G = g;
}

public static TextView getH() {
    return H;
}

public static void setH(TextView h) {
    H = h;
}

public static TextView getCC() {
    return CC;
}

public static void setCC(TextView CC) {
    Model.CC = CC;
}

public static TextView getDD() {
    return DD;
}

public static void setDD(TextView DD) {
    Model.DD = DD;
}

public static TextView getCs() {
    return cs;
}

public static void setCs(TextView cs) {
    Model.cs = cs;
}

public static TextView getScore() {
    return score;
}

public static void setScore(TextView score) {
    Model.score = score;
}

public static TextView getUnticked() {
    return unticked;
}

public static void setUnticked(TextView unticked) {
    Model.unticked = unticked;
}

public static Button getNext_test() {
    return next_test;
}

public static void setNext_test(Button next_test) {
    Model.next_test = next_test;
}

public static Button getButton() {
    return button;
}

public static void setButton(Button button) {
    Model.button = button;
}

public static Button getNewpatient() {
    return newpatient;
}

public static void setNewpatient(Button newpatient) {
    Model.newpatient = newpatient;
}

public static Button getOldpatient() {
    return oldpatient;
}

public static void setOldpatient(Button oldpatient) {
    Model.oldpatient = oldpatient;
}

public static RadioGroup getR() {
    return r;
}

public static void setR(RadioGroup r) {
    Model.r = r;
}

public static CheckBox getCheckTinetti() {
    return checkTinetti;
}

public static void setCheckTinetti(CheckBox checkTinetti) {
    Model.checkTinetti = checkTinetti;
}

public static CheckBox getCheckEfficacy() {
    return checkEfficacy;
}

public static void setCheckEfficacy(CheckBox checkEfficacy) {
    Model.checkEfficacy = checkEfficacy;
}

public static CheckBox getCheckFRAT() {
    return checkFRAT;
}

public static void setCheckFRAT(CheckBox checkFRAT) {
    Model.checkFRAT = checkFRAT;
}

public static CheckBox getCheckMorse() {
    return checkMorse;
}

public static void setCheckMorse(CheckBox checkMorse) {
    Model.checkMorse = checkMorse;
}

}

Answer 1

我不明白你不想做什么。您不应将一个活动中的观点引用传递给另一个活动，也不应引用视图static。活动的生命周期由操作系统处理，并且在对活动调用onDestroy之后，其对象可能被垃圾收集（这就是为什么你得到空指针异常）。

Answer 2

当您执行findViewById时，必须在setContentView期间膨胀的activity_main.xml文件中定义具有您想要的id的视图。

在您的MorseFalls活动中，您通过新的MainActivity（）创建了一个新的MainActivity实例。这只是创建一个Java对象 - 它不会调用onCreate。因此，activity_main.xml没有为您充气，并且无法找到视图。现在，谁负责调用活动的生命周期方法，如onCreate和onDestroy？系统会调用它，而不是你。

在任何情况下，请不要将活动视为仅仅是另一个Java类。它不止于此。每个活动必须在清单中声明，操作系统将处理活动的生命周期（例如，当用户最小化您的应用程序时，会自动调用onPause然后onStop活动）。通常，您不应该在活动之间传递引用以防止内存问题。您甚至不应该通过构造函数实例化活动。

如果要重新使用方法，请将它们放在不从任何活动扩展的单独类中。此外，每个活动都应该有自己的布局文件，因此应该有自己的视图，因此应该没有理由重新使用对完全相同的布局文件进行操作的方法，因此也就是相同的视图。

主要活动的方法不进入其他活动

2 个答案: