Question

XML文件有16 EditText用于输入8个科目和相关成绩点的分数，1 TextView用于显示输出和1 Button。

这是我的代码：

package com.workingbros.ak.myapplication;

import android.support.v7.app.AppCompatActivity;
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 {
EditText s1,s2,s3,s4,s5,s6,s7,s8,g1,g2,g3,g4,g5,g6,g7,g8; //Declaring the variables of EditText widget
TextView cgpa; //Declaring the variaple for TextView widget
Button submit;// Declaring the variable for Button widget
int i;
Double sub[],gr[],fin[],res=0.0, sumg=0.0;
    @Override
      protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);


            s1 = findViewById(R.id.s1);
            s2 = findViewById(R.id.s2);   
            s3 = findViewById(R.id.s3);
            s4 = findViewById(R.id.s4);
            s5 = findViewById(R.id.s5);
            s6 = findViewById(R.id.s6);
            s7 = findViewById(R.id.s7);
            s8 = findViewById(R.id.s8);
            g1 = findViewById(R.id.g1);
            g2 = findViewById(R.id.g2);
            g3 = findViewById(R.id.g3);
            g4 = findViewById(R.id.g4);
            g5 = findViewById(R.id.g5);
            g6 = findViewById(R.id.g6);
            g7 = findViewById(R.id.g7);
            g8 = findViewById(R.id.g8);
            submit=findViewById(R.id.submit);
            cgpa= findViewById(R.id.cgpa);

        submit.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
       for (i = 1; i <= 8; i++) {
                         sub[i] = 0.0;
                         gr[i] = 0.0;
                         fin[i] = 0.0;

                }


       //Storing the value from si textfield in sub[i] which is the marks of each subject and gi textfield  in gr[i] which is the grade point.

                 sub[1]= Double.parseDouble(s1.getText().toString());
                 sub[2]= Double.parseDouble(s2.getText().toString());
                 sub[3]= Double.parseDouble(s3.getText().toString());
                 sub[4]= Double.parseDouble(s4.getText().toString());
                 sub[5]= Double.parseDouble(s5.getText().toString());
                 sub[6]= Double.parseDouble(s6.getText().toString());
                 sub[7]= Double.parseDouble(s7.getText().toString());
                 sub[8]= Double.parseDouble(s8.getText().toString());
                 gr[1]= Double.parseDouble(g1.getText().toString()); 
                 gr[2]= Double.parseDouble(g2.getText().toString());
                 gr[3]= Double.parseDouble(g3.getText().toString());
                 gr[4]= Double.parseDouble(g4.getText().toString());
                 gr[5]= Double.parseDouble(g5.getText().toString());
                 gr[6]= Double.parseDouble(g6.getText().toString());
                 gr[7]= Double.parseDouble(g7.getText().toString());
                 gr[8]= Double.parseDouble(g8.getText().toString());
  //Assigning values of marks

                     for(i=1;i<=8;i++) {

                    if(sub[i]>=90&&sub[i]<=100)
                        fin[i]=10.0;
                    else if(sub[i]>=80&&sub[i]<90)
                        fin[i]=9.0;
                    else if(sub[i]>=70&&sub[i]<80)
                        fin[i]=8.0;
                    else if(sub[i]>=60&&sub[i]<70)
                        fin[i]=7.0;
                    else if(sub[i]>=50&&sub[i]<60)
                        fin[i]=6.0;
                    else
                        fin[i]=0.0; // which is fail
                    sumg=sumg+gr[i]; // total grade point in a semester
                }
                for(i=1;i<=8;i++) {
                    if(fin[i]!=0.0)
                        res = res + (fin[i]*gr[i]);

                }
                cgpa.setText(String.valueOf(res/sumg)); // printing the value
            }

    });
}}

它计算CGPA。注意：我是android studio的初学者。

Logcat报告：

E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.workingbros.ak.myapplication, PID: 22410
    java.lang.NullPointerException: Attempt to write to null array
        at com.workingbros.ak.myapplication.MainActivity$1.onClick(MainActivity.java:71)
        at android.view.View.performClick(View.java:6256)
        at android.view.View$PerformClick.run(View.java:24701)
        at android.os.Handler.handleCallback(Handler.java:789)
        at android.os.Handler.dispatchMessage(Handler.java:98)
        at android.os.Looper.loop(Looper.java:172)
        at android.app.ActivityThread.main(ActivityThread.java:6637)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:767)

Answer 1

您必须初始化<div id="launches"> <section class="launch" v-for="launch in launches"> <h3 class="rocket">{{launch.rocket.name}}</h3> <p>Rocket: {{launch.rocket.name}}</p> <p>LSP: {{launch.lsp}}</p> <p>Webcast: {{launch.vidURLs[0]}}</p> <p>NET: {{launch.net}}</p> <p>Location: {{launch.location.name}}</p> </section> </div> <script type="text/javascript"> const vm = new Vue({ el: '#launches', data: { launches: [] }, mounted() { this.getLaunches(); }, methods: { getLaunches() { axios.get('https://launchlibrary.net/1.3/launch?next=5&mode=verbose') .then((response) => { this.launches = response.data.launches; console.log(this.launches); }) .catch(error => {console.log(error); }); } } }); </script>数组。您正在为不同的sub[],gr[],fin[]对象设置值。 Double是一个容器，没有初始化数组，不为其元素分配内存。在Array

之后初始化数组

setContentView(R.layout.activity_main);

Android Studio：当我点击提交按钮时，App force会关闭

1 个答案: