Android应用程序在RatingBar DialogFragment关闭后崩溃

Question

我的应用程序的目的是通过一个自定义对话框从一个评级栏中检索一个值（5分），并将其显示在主activity的一个TextView中。当我点击我在下图中用红色勾勒出来的按钮时，应用程序崩溃并关闭。

该应用程序由2个类/活动组成。主activity和自定义对话框activity。

这两个文件的代码可以在下面找到：

mainactivity.java：

package com.example.mealrater;

import androidx.appcompat.app.AppCompatActivity;
import androidx.fragment.app.FragmentManager;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;

public class MainActivity extends AppCompatActivity implements MealRaterDialog.SaveRating {

    public EditText restaurant, dish;
    public TextView ratingDisplay;

    @Override
    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        restaurant = findViewById(R.id.etRestaurant);
        dish = findViewById(R.id.etDish);

        RateMealButton();

    }

    @Override
    public void finishMealRaterDialog(String rating) {
        ratingDisplay = findViewById(R.id.tvRatingDisplay);
        ratingDisplay.setText(rating);
    }

    private void RateMealButton() {

        Button rate = findViewById(R.id.btnRate);
        rate.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View view) {

                FragmentManager fm = getSupportFragmentManager();
                MealRaterDialog mealRaterDialog = new MealRaterDialog();
                mealRaterDialog.show(fm, "RateMeal");

            }
        });
    }
}

mealRaterDialog.java：

package com.example.mealrater;

import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.RatingBar;
import androidx.fragment.app.DialogFragment;

public class MealRaterDialog extends DialogFragment {

    String rating;

    public interface SaveRating {
        void finishMealRaterDialog(String rating);
    }

    public MealRaterDialog() {
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {

        final View view = inflater.inflate(R.layout.meal_rater, container);
        getDialog().setTitle("Rate your meal");

        Button save = view.findViewById(R.id.btnSaveRating);
        save.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View view) {

                RatingBar ratingBar = view.findViewById(R.id.rbMeal);
                rating = String.valueOf(ratingBar.getRating());
                SaveItem(String.valueOf(rating));

            }
        });
        return view;
    }

    private void SaveItem(String rating) {

        MealRaterDialog.SaveRating activity = (MealRaterDialog.SaveRating) getActivity();
        activity.finishMealRaterDialog(rating);
        getDialog().dismiss();

    }
}

我是Android Studio的新手，我也想知道如何改进这个问题。谢谢你。

Logcat错误：

2021-04-28 16:04:35.240 18144-18144/com.example.mealrater E/libc: Access denied finding property "ro.serialno"
2021-04-28 16:04:42.709 18144-18144/com.example.mealrater E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.mealrater, PID: 18144
    java.lang.NullPointerException: Attempt to invoke virtual method 'float android.widget.RatingBar.getRating()' on a null object reference
        at com.example.mealrater.MealRaterDialog$1.onClick(MealRaterDialog.java:35)
        at android.view.View.performClick(View.java:7448)
        at com.google.android.material.button.MaterialButton.performClick(MaterialButton.java:1119)
        at android.view.View.performClickInternal(View.java:7425)
        at android.view.View.access$3600(View.java:810)
        at android.view.View$PerformClick.run(View.java:28305)
        at android.os.Handler.handleCallback(Handler.java:938)
        at android.os.Handler.dispatchMessage(Handler.java:99)
        at android.os.Looper.loop(Looper.java:223)
        at android.app.ActivityThread.main(ActivityThread.java:7656)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:592)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:947)

Answer 1

对此有很多修补方法。

首先，您应该在onclick之前定义ratingBar小部件。现在，当您每次单击按钮时，它都在创建变量。在按钮保存=view.findViewById(r.id.btnsaverating)；行之后定义它。

其次，当您正在使用对话框片段时，应该在名为onViewCreated()的覆盖函数中调用单击的所有逻辑。而不是像现在这样在onCreateView()中。如果对你有用就告诉我。