Question

我希望用户在一个EditText窗口小部件中输入他的名字，然后在其他EditText窗口小部件中输入他的权重，然后将该数据从一个活动转移到另一个活动。

重量输入应该稍后包含在一个公式中，名称输入应该在TextView小部件中与公式结果一起确定。

但是，当我启动我的应用时，最终Android Studio会向我显示NullPointerException。我认为错误是活动之间数据共享的某个方面。所以，这是代码。如果可以的话，请帮助我:)。

ActivityOne（活动名称为InformacijeM）XML文件：

  <?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/activity_informacije_m"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="com.example.alkometar.InformacijeM"
    android:background="@drawable/activitybackground">

    <TextView
        android:text="Ukucaj svoje ime"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentTop="true"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="29dp"
        android:textSize="25dp"
        android:textColor="@android:color/black"
        android:textStyle="bold"
        android:id="@+id/UkucajIme" />


    <ImageButton
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        app:srcCompat="@drawable/strelamanja"
        android:id="@+id/strelica"
        android:layout_alignParentBottom="true"
        android:layout_centerHorizontal="true"
        android:layout_marginBottom="28dp" />

    <EditText
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:inputType="textPersonName"
        android:text=""
        android:ems="10"
        android:id="@+id/ImeInput"
        android:layout_marginTop="12dp"
        android:layout_below="@+id/UkucajIme"
        android:layout_alignParentLeft="true"
        android:layout_alignParentStart="true"
        />

    <EditText
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:inputType="textPersonName"
        android:text=""
        android:ems="10"
        android:id="@+id/MasaInput"
        android:layout_marginBottom="53dp"
        android:layout_above="@+id/strelica"
        android:layout_alignParentLeft="true"
        android:layout_alignParentStart="true"
        />

    <TextView
        android:text="Ukucaj svoju masu u kg"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/UkucajMasu"
        android:textSize="25dp"
        android:textColor="@android:color/black"
        android:textStyle="bold"
        android:layout_marginBottom="30dp"
        android:layout_above="@+id/MasaInput"
        android:layout_centerHorizontal="true" />

</RelativeLayout>

ActivityOne（InformacijeM）Java文件：

    package com.example.alkometar;

import android.content.Intent;
import android.content.res.Resources;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.EditText;
import android.widget.ImageButton;

public class InformacijeM extends AppCompatActivity {

    EditText ImeTxt, MasaTxt ;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_informacije_m);

        // INICIRANJE VREDNOSTI


        EditText ImeTxt = (EditText)findViewById(R.id.ImeInput);
        final String str1 = ImeTxt.getText().toString();

        EditText MasaTxt = (EditText)findViewById(R.id.MasaInput);
        final String str2 = MasaTxt.getText().toString();

        ImageButton btn = (ImageButton)findViewById(R.id.strelica);
        // PREBACIVANJE AKTIVITIJA
        btn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent intent1 = new Intent(InformacijeM.this, RezultatM.class);
                intent1.putExtra("keyIme", str1);
                intent1.putExtra("keyMasa", str2);

                Intent intent = new Intent(InformacijeM.this, StanjeM.class);
                startActivity(intent);


            }
        });
    }}

ActivityTwo（活动名称为RezultatM）XML文件：

    <?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/activity_rezultat_m"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="com.example.alkometar.RezultatM"
    android:background="@drawable/activitybackground">

    <TextView
        android:text=""
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentTop="true"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="97dp"
        android:id="@+id/rezultatTekst" />

    <Button
        android:text="Rezultat"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentTop="true"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="26dp"
        android:id="@+id/button" />
</RelativeLayout>

ActivityTwo（RezultatM）Java文件：

    package com.example.alkometar;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;

public class RezultatM extends AppCompatActivity {


    TextView rezultat;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_rezultat_m);


        rezultat = (TextView) findViewById(R.id.rezultatTekst);
        Button button = (Button) findViewById(R.id.button);

        button.setOnClickListener(new View.OnClickListener() {
            public void onClick(View view) {
               Bundle extras = getIntent().getExtras();
                 {
                    String str1 = extras.getString("keyIme");
                    String str2 = extras.getString("keyMasa");


                double masad = Double.valueOf(str2);
                double nekibroj = 0.8;
                double result = masad * nekibroj;

                rezultat.setText(str1 + "Nivo alkohola u tvojoj krvi je:" + result);
            }
        };
        });
    }}

Strings.xml文件：

    <resources>
    <string name="app_name">Alkometar</string>
    <string name="ImeInput">ImeInput</string>
    <string name="MasaInput">MasaInput</string>

</resources>

AndroidManifest XML文件：

    <?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.alkometar">

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity android:name=".Pol">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        <activity android:name=".InformacijeM" />
        <activity android:name=".StanjeM" />
        <activity android:name=".InformacijeZ" />
        <activity android:name=".StanjeZ" />
        <activity android:name=".PijemM" />
        <activity android:name=".RezultatM"></activity>
    </application>

</manifest>

这是logCat中的例外：

E/AndroidRuntime: FATAL EXCEPTION: main
              Process: com.example.alkometar, PID: 30732
              java.lang.NullPointerException
                  at com.example.alkometar.RezultatM$1.onClick(RezultatM.java:28)
                  at android.view.View.performClick(View.java:4463)
                  at android.view.View$PerformClick.run(View.java:18770)
                  at android.os.Handler.handleCallback(Handler.java:808)
                  at android.os.Handler.dispatchMessage(Handler.java:103)
                  at android.os.Looper.loop(Looper.java:193)
                  at android.app.ActivityThread.main(ActivityThread.java:5292)
                  at java.lang.reflect.Method.invokeNative(Native Method)
                  at java.lang.reflect.Method.invoke(Method.java:515)
                  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:824)
                  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:640)
                  at dalvik.system.NativeStart.main(Native Method)

再次非常感谢！：）））

Answer 1

将您的活动二课程更改为：

public class RezultatM extends AppCompatActivity {


TextView rezultat;
String str1,str2;
double masad;
public static final String MyPREFERENCES = "MyPrefs";
SharedPreferences sharedPreferences;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_rezultat_m);


    rezultat = (TextView) findViewById(R.id.rezultatTekst);
    Button button = (Button) findViewById(R.id.button);
    //Intent intent = getIntent();
    //str1 = intent.getStringExtra("keyIme");
    //str2 = intent.getStringExtra("keyMasa"); 
    //getting values from shared preferences
     SharedPreferences shared = getSharedPreferences(MyPREFERENCES, Context.MODE_PRIVATE); 
    str1=shared.getString("keyIme", "");
    str2=shared.getString("keyMasa", "");
    button.setOnClickListener(new View.OnClickListener() {
        public void onClick(View view) {

            if(str2!=null){
            masad = Double.parseDouble(str2);
            }
            double nekibroj = 0.8;
            double result = masad * nekibroj;

            rezultat.setText(str1 + "Nivo alkohola u tvojoj krvi je:" + result);
    };
    });
}}

同样在你的活动一中，你开始错误的意图

 Intent intent1 = new Intent(InformacijeM.this, RezultatM.class);
 intent1.putExtra("keyIme", str1);
 intent1.putExtra("keyMasa", str2);

 Intent intent = new Intent(InformacijeM.this, StanjeM.class);
// startActivity(intent); //here you are starting another class..check it
//change it to
startActivity(intent1);

更改您的InformacijeM.java类：

    public class InformacijeM extends AppCompatActivity {

    EditText ImeTxt, MasaTxt ;
    public static final String MyPREFERENCES = "MyPrefs";
    SharedPreferences sharedPreferences;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_informacije_m);
        sharedPreferences = getSharedPreferences(MyPREFERENCES, Context.MODE_PRIVATE);

        // INICIRANJE VREDNOSTI


        EditText ImeTxt = (EditText)findViewById(R.id.ImeInput);
        final String str1 = ImeTxt.getText().toString();

        EditText MasaTxt = (EditText)findViewById(R.id.MasaInput);
        final String str2 = MasaTxt.getText().toString();
        save_data(str1,str2);
        ImageButton btn = (ImageButton)findViewById(R.id.strelica);
        // PREBACIVANJE AKTIVITIJA
        btn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent intent1 = new Intent(InformacijeM.this, RezultatM.class);
                intent1.putExtra("keyIme", str1);
                intent1.putExtra("keyMasa", str2);

                Intent intent = new Intent(InformacijeM.this, StanjeM.class);
                startActivity(intent);


            }
        });
    }

    public void save_data(String s1,String s2){
         SharedPreferences.Editor editor = sharedPreferences.edit();
         editor.putString("keyIme", s1);
         editor.putString("keyMasa", s2);
         editor.commit();
         }  
}

在活动之间传递用户输入（EditText），然后在公式

1 个答案: