使用左右滑动导航进行JSON解析

Question

我的Android应用程序有问题。它不会显示我想要的json项目。

如果我打开应用程序，它应显示第一个任务，如果我向左滑动它应显示下一个任务（向右滑动应显示上一个任务）。

我知道有一些不需要的和错误的代码..

json数据看起来像这样：

{
    "missionen": [
        {
            "nr": 1,
            "n": "n1",
            "sd": "sd1",
            "oc": "oc1",
            "s": "s1"
        },
        {
            "nr": 2,
            "n": "n2",
            "sd": "sd2",
            "oc": "oc2",
            "s": "s2"
        }
    ]
}

activity_main.xml中

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:ads="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="net.xairon.colm.MainActivity">

<!-- view for AdMob Banner Ad -->

<com.google.android.gms.ads.AdView
    android:id="@+id/adView"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignParentBottom="true"
    android:layout_centerHorizontal="true"
    ads:adSize="BANNER"
    ads:adUnitId="@string/banner_ad_unit_id" />

<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="Mission:"
    android:layout_alignParentTop="true"
    android:layout_alignParentLeft="true"
    android:layout_alignParentStart="true"
    android:id="@+id/tvNr"
    android:textSize="21sp"
    android:layout_margin="10dp"
    android:textColor="@color/colorPrimaryDark" />

<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="name"
    android:id="@+id/tvN"
    android:textColor="@color/colorPrimaryDark"
    android:textSize="23sp"
    android:layout_above="@+id/tvSd"
    android:layout_centerHorizontal="true"
    android:layout_margin="10dp" />

<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="start date"
    android:id="@+id/tvSd"
    android:textColor="@color/colorPrimaryDark"
    android:textSize="16sp"
    android:layout_above="@+id/tvOc"
    android:layout_centerHorizontal="true"
    android:layout_margin="10dp" />

<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="organisation, country"
    android:id="@+id/tvOc"
    android:textColor="@color/colorPrimaryDark"
    android:textSize="18sp"
    android:layout_above="@+id/tvS"
    android:layout_centerHorizontal="true"
    android:layout_margin="10dp" />

<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="stage"
    android:id="@+id/tvS"
    android:textColor="@color/colorPrimaryDark"
    android:layout_centerVertical="true"
    android:layout_centerHorizontal="true" />

</RelativeLayout>

和我的MainActivity.java

package net.xairon.colm;

import com.google.android.gms.ads.AdRequest;
import com.google.android.gms.ads.AdView;

import android.content.Context;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.TextView;

import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.ArrayList;

public class MainActivity extends AppCompatActivity {

    public TextView tv_nr, tv_n, tv_sd, tv_oc, tv_s;
    public int count = 0;
    public String m;
    InputStream inputstream;
    BufferedReader reader;
    ArrayList<MissionClass> missions;

    public class MissionClass {
        public int nr;
        public String n, sd, oc, s;
    }

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        LayoutInflater inflater = (LayoutInflater) getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        View view = inflater.inflate(R.layout.activity_main, null);
        setContentView(view);

        AdView adView = (AdView) findViewById(R.id.adView);
        AdRequest adRequest = new AdRequest.Builder().setRequestAgent("android_studio:ad_template").build();
        adView.loadAd(adRequest);

        try {
            inputstream = getResources().getAssets().open("colm_new.json");
            reader = new BufferedReader(new InputStreamReader(inputstream));

            m = reader.toString();
            StringBuilder total = new StringBuilder();
            String line;
            while ((line = reader.readLine()) != null) {
                total.append(line);
            }
            m = total.toString();
        } catch (IOException ex) {
            ex.printStackTrace();
        }

        count++;
        setValues(count);

        view.setOnTouchListener(new OnSwipeTouchListener(MainActivity.this) {
            public void onSwipeTop() {
            }
            public void onSwipeRight() {
            }
            public void onSwipeLeft() {
                if (count == missions.size() - 1) {
                    finish();
                } else {
                    count++;
                    setValues(count);
                }
            }
            public void onSwipeBottom() {
            }
        });
    }

    public void JSONParser() {
        missions = new ArrayList<>();

        try {
            JSONObject jsonObjMain = new JSONObject(m);
            JSONArray jsonArray = jsonObjMain.getJSONArray("missionen");

            for (int i = 0; i < jsonArray.length(); i++) {
                JSONObject jO = jsonArray.getJSONObject(i);

                MissionClass missionClass = new MissionClass();
                missionClass.nr = jO.getInt("nr");
                missionClass.n = jO.getString("n");
                missionClass.sd = jO.getString("sd");
                missionClass.oc =jO.getString("oc");
                missionClass.s = jO.getString("s");
                missions.add(missionClass);
            }

        } catch (JSONException e) {
            e.printStackTrace();
        }
    }

    public void setValues(int j) {
        tv_nr.setText(missions.get(j).nr);
        tv_n.setText(missions.get(j).n);
        tv_sd.setText(missions.get(j).sd);
        tv_oc.setText(missions.get(j).oc);
        tv_s.setText(missions.get(j).s);
    }

    @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();

        if (id == R.id.action_about) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }

}

错误日志

09-10 20:16:58.131 16906-16906/net.xairon.colm E/AndroidRuntime: FATAL EXCEPTION: main
 Process: net.xairon.colm, PID: 16906
 java.lang.RuntimeException: Unable to start activity ComponentInfo{net.xairon.colm/net.xairon.colm.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.Object java.util.ArrayList.get(int)' on a null object reference
     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3253)
     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3349)
     at android.app.ActivityThread.access$1100(ActivityThread.java:221)
     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1794)
     at android.os.Handler.dispatchMessage(Handler.java:102)
     at android.os.Looper.loop(Looper.java:158)
     at android.app.ActivityThread.main(ActivityThread.java:7224)
     at java.lang.reflect.Method.invoke(Native Method)
     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230)
     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120)
  Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.Object java.util.ArrayList.get(int)' on a null object reference
     at net.xairon.colm.MainActivity.setValues(MainActivity.java:111)
     at net.xairon.colm.MainActivity.onCreate(MainActivity.java:66)
     at android.app.Activity.performCreate(Activity.java:6876)
     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1135)
     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3206)
     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3349) 
     at android.app.ActivityThread.access$1100(ActivityThread.java:221) 
     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1794) 
     at android.os.Handler.dispatchMessage(Handler.java:102) 
     at android.os.Looper.loop(Looper.java:158) 
     at android.app.ActivityThread.main(ActivityThread.java:7224) 
     at java.lang.reflect.Method.invoke(Native Method) 
     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230) 
     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120) 

Answer 1

按如下方式创建课程

Class MyClass{
    public int nr;
    public String n;
    public String sd;
    public String oc;
    public String s;
}

并创建List，如下所示

ArrayList<MyClass> missions = new ArrayList<>();

并按如下方式解析你的json

JSONObject jsonObjMain = new JSONObject(m);
JSONArray jsonArray = jsonObjMain.getJSONArray("missionen");

for (int i = 0; i < jsonArray.length(); i++) {
    JSONObject jO = jsonArray.getJSONObject(i);

    MyClass myClass = new MyClass();
    myClass.nr = jO.getInt("nr");
    myClass.n = jO.getString("n");
    myClass..sd = jO.getString("sd");
    myClass.oc = jO.getString("oc");
    myClass.s = jO.getString("s");
    missions.add(myClass);
}

修改 - 您的setValues()方法也应如下

public void setValues(int j) {
    tv_nr.setText(""+missions.get(j).nr);
    tv_n.setText(missions.get(j).n);
    tv_sd.setText(missions.get(j).sd);
    tv_oc.setText(missions.get(j).oc);
    tv_s.setText(missions.get(j).c);
}