在调用方法时在android片段中获取NullPointerException

Question

我有一个带有复选框和重置按钮的android片段。 片段内部有更新和重置方法。 每当我调用这些方法时，我都会得到一个NullPointerException。 我无法弄清楚为什么（这让我成为新手）

package info.doktershuis.android.jichtcalculator;


public class CalculatorFragment extends Fragment implements View.OnClickListener {

double score = 0;
double man = 2;
double manPl = 0;

public CalculatorFragment() {
    // Required empty public constructor
}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    // Inflate the layout for this fragment

    View layout = inflater.inflate(R.layout.fragment_calculator, container, false);

    CheckBox cbGeslacht = (CheckBox)layout.findViewById(R.id.cbGeslacht);
    cbGeslacht.setOnClickListener(this);

    Button reset = (Button) layout.findViewById(R.id.button);
    reset.setOnClickListener(this);

    TextView punt = (TextView) layout.findViewById(R.id.tvPunt);
    TextView perc = (TextView) layout.findViewById(R.id.tvPercentage);
    TextView advies = (TextView) layout.findViewById(R.id.tvToelicht);

    punt.setText(Double.toString(score));
    perc.setText(R.string.pt4);
    perc.setBackgroundColor(getResources().getColor(holo_green_light));
    advies.setText(R.string.pt4a);

    return layout;
}

public void reset(View view) {

    CheckBox geslacht = (CheckBox) view.findViewById(R.id.cbGeslacht);

    TextView punt = (TextView) view.findViewById(R.id.tvPunt);
    TextView perc = (TextView) view.findViewById(R.id.tvPercentage);
    TextView advies = (TextView) view.findViewById(R.id.tvToelicht);

    geslacht.setChecked(false);

    double score = 0;
    manPl = 0;

    punt.setText(Double.toString(score));
    perc.setText(R.string.pt4);
    perc.setBackgroundColor(getResources().getColor(holo_green_light));
    advies.setText(R.string.pt4a);

}

public void update(View view) {

    TextView punt = (TextView) view.findViewById(R.id.tvPunt);
    TextView perc = (TextView) view.findViewById(R.id.tvPercentage);
    TextView advies = (TextView) view.findViewById(R.id.tvToelicht);

    score = manPl;
    punt.setText(Double.toString(score));

    if (score <= 4) {
        perc.setText(R.string.pt4);
        perc.setBackgroundColor(getResources().getColor(holo_green_light));
        advies.setText(R.string.pt4a);
    } else if (score < 8) {
        perc.setText(R.string.pt48);
        perc.setBackgroundColor(getResources().getColor(holo_orange_light));
        advies.setText(R.string.pt48a);
    } else {
        perc.setText(R.string.pt8);
        perc.setBackgroundColor(getResources().getColor(holo_red_light));
        advies.setText(R.string.pt8a);
    }

}

@Override
public void onClick(View view) {

    CheckBox geslacht = (CheckBox) view.findViewById(R.id.cbGeslacht);

    switch (view.getId()) {
        case R.id.cbGeslacht:
            if (geslacht.isChecked()) {
                manPl = man;
            } else {
                manPl = 0;
            }
            update(view);
            break;
        case R.id.button:
            reset(view);
            break;
    }

}

}

当我使用geslacht.setChecked(false);或punt.setText(Double.toString(score));时，会抛出异常 任何人都可以帮助我这个，非常感谢提前

logcat的：

01-21 08:43:25.233 23876-23876/info.doktershuis.android.jichtcalculator E/AndroidRuntime: FATAL EXCEPTION: main
                                                                                      java.lang.NullPointerException
                                                                                          at info.doktershuis.android.jichtcalculator.CalculatorFragment.reset(CalculatorFragment.java:111)
                                                                                          at info.doktershuis.android.jichtcalculator.CalculatorFragment.onClick(CalculatorFragment.java:278)
                                                                                          at android.view.View.performClick(View.java:4204)
                                                                                          at android.view.View$PerformClick.run(View.java:17355)
                                                                                          at android.os.Handler.handleCallback(Handler.java:725)
                                                                                          at android.os.Handler.dispatchMessage(Handler.java:92)
                                                                                          at android.os.Looper.loop(Looper.java:137)
                                                                                          at android.app.ActivityThread.main(ActivityThread.java:5041)
                                                                                          at java.lang.reflect.Method.invokeNative(Native Method)
                                                                                          at java.lang.reflect.Method.invoke(Method.java:511)
                                                                                          at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
                                                                                          at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
                                                                                          at dalvik.system.NativeStart.main(Native Method)

嗨K Neeraj Lal（SO-not-ready to help），我已经阅读了有关NullPointerException的所有内容。找不到我的答案。请指出我在哪里找到它。记住我是新手。我可能不会理解这一切。

Answer 1

由于我没有看到您的错误日志，但仍有少数观察可能导致Null指针异常。

您每次使用按钮视图在按钮单击方法中投射视图。喜欢这里

public void update(View view) {

    TextView punt = (TextView) view.findViewById(R.id.tvPunt);
    TextView perc = (TextView) view.findViewById(R.id.tvPercentage);
    TextView advies = (TextView) view.findViewById(R.id.tvToelicht);

在这里

public void reset(View view) {

    CheckBox geslacht = (CheckBox) view.findViewById(R.id.cbGeslacht);

    TextView punt = (TextView) view.findViewById(R.id.tvPunt);
    TextView perc = (TextView) view.findViewById(R.id.tvPercentage);
    TextView advies = (TextView) view.findViewById(R.id.tvToelicht);

最好将这些视图设为全局视图，并从update和reset方法中删除这些视图，因为您已经在onCreateView方法中添加了这些视图。 lemme知道问题是否解决，或者发布错误日志。 ：）

这里是样本

public class CalculatorFragment extends Fragment implements View.OnClickListener {

    double score = 0;
    double man = 2;
    double manPl = 0;

    CheckBox cbGeslacht;

    TextView punt;
    TextView perc;
    TextView advies;

    public CalculatorFragment() {
        // Required empty public constructor
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // Inflate the layout for this fragment

        View layout = inflater.inflate(R.layout.fragment_calculator, container, false);

        cbGeslacht = (CheckBox)layout.findViewById(R.id.cbGeslacht);
        cbGeslacht.setOnClickListener(this);

        Button reset = (Button) layout.findViewById(R.id.button);
        reset.setOnClickListener(this);

        punt = (TextView) layout.findViewById(R.id.tvPunt);
        perc = (TextView) layout.findViewById(R.id.tvPercentage);
        advies = (TextView) layout.findViewById(R.id.tvToelicht);

        punt.setText(Double.toString(score));
        perc.setText(R.string.pt4);
        perc.setBackgroundColor(getResources().getColor(holo_green_light));
        advies.setText(R.string.pt4a);

        return layout;
    }

    public void reset(View view) {

        cbGeslacht.setChecked(false);

        double score = 0;
        manPl = 0;

        punt.setText(Double.toString(score));
        perc.setText(R.string.pt4);
        perc.setBackgroundColor(getResources().getColor(holo_green_light));
        advies.setText(R.string.pt4a);

    }

    public void update(View view) {

        score = manPl;
        punt.setText(Double.toString(score));

        if (score <= 4) {
            perc.setText(R.string.pt4);
            perc.setBackgroundColor(getResources().getColor(holo_green_light));
            advies.setText(R.string.pt4a);
        } else if (score < 8) {
            perc.setText(R.string.pt48);
            perc.setBackgroundColor(getResources().getColor(holo_orange_light));
            advies.setText(R.string.pt48a);
        } else {
            perc.setText(R.string.pt8);
            perc.setBackgroundColor(getResources().getColor(holo_red_light));
            advies.setText(R.string.pt8a);
        }

    }

    @Override
    public void onClick(View view) {


        switch (view.getId()) {
            case R.id.cbGeslacht:
                if (cbGeslacht.isChecked()) {
                    manPl = man;
                } else {
                    manPl = 0;
                }
                update(view);
                break;
            case R.id.button:
                reset(view);
                break;
        }

    }

}

Answer 2

您可以使用布局而不是获取按钮视图来获取其他项目。

试试这个

public class CalculatorFragment extends Fragment implements View.OnClickListener {

    double score = 0;
    double man = 2;
    double manPl = 0;
    View layout;
    public CalculatorFragment() {
        // Required empty public constructor
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // Inflate the layout for this fragment

         layout = inflater.inflate(R.layout.fragment_calculator, container, false);

        CheckBox cbGeslacht = (CheckBox)layout.findViewById(R.id.cbGeslacht);
        cbGeslacht.setOnClickListener(this);

        Button reset = (Button) layout.findViewById(R.id.button);
        reset.setOnClickListener(this);

        TextView punt = (TextView) layout.findViewById(R.id.tvPunt);
        TextView perc = (TextView) layout.findViewById(R.id.tvPercentage);
        TextView advies = (TextView) layout.findViewById(R.id.tvToelicht);

        punt.setText(Double.toString(score));
        perc.setText(R.string.pt4);
        perc.setBackgroundColor(getResources().getColor(holo_green_light));
        advies.setText(R.string.pt4a);

        return layout;
    }

    public void reset(View view) {

        CheckBox geslacht = (CheckBox) layout.findViewById(R.id.cbGeslacht);

        TextView punt = (TextView) layout.findViewById(R.id.tvPunt);
        TextView perc = (TextView) layout.findViewById(R.id.tvPercentage);
        TextView advies = (TextView) layout.findViewById(R.id.tvToelicht);

        geslacht.setChecked(false);

        double score = 0;
        manPl = 0;

        punt.setText(Double.toString(score));
        perc.setText(R.string.pt4);
        perc.setBackgroundColor(getResources().getColor(holo_green_light));
        advies.setText(R.string.pt4a);

    }

    public void update(View view) {

        TextView punt = (TextView) layout.findViewById(R.id.tvPunt);
        TextView perc = (TextView) layout.findViewById(R.id.tvPercentage);
        TextView advies = (TextView) layout.findViewById(R.id.tvToelicht);

        score = manPl;
        punt.setText(Double.toString(score));

        if (score <= 4) {
            perc.setText(R.string.pt4);
            perc.setBackgroundColor(getResources().getColor(holo_green_light));
            advies.setText(R.string.pt4a);
        } else if (score < 8) {
            perc.setText(R.string.pt48);
            perc.setBackgroundColor(getResources().getColor(holo_orange_light));
            advies.setText(R.string.pt48a);
        } else {
            perc.setText(R.string.pt8);
            perc.setBackgroundColor(getResources().getColor(holo_red_light));
            advies.setText(R.string.pt8a);
        }

    }

    @Override
    public void onClick(View view) {

        CheckBox geslacht = (CheckBox) layout.findViewById(R.id.cbGeslacht);

        switch (view.getId()) {
            case R.id.cbGeslacht:
                if (geslacht.isChecked()) {
                    manPl = man;
                } else {
                    manPl = 0;
                }
                update(view);
                break;
            case R.id.button:
                reset(view);
                break;
        }

    }

}