Question

按钮工作正常（没有崩溃）但是在我做完后它会将信息写入ArrayList ListView（尚未使用）它开始崩溃。造成这种情况的原因是什么以及如何解决？

我添加的代码（不同的活动，但我通过startActivityForResult使用按钮进行活动。它获取onActivityResult中声明的信息，另一个函数放置所有信息进入ArrayList：

@Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        super.onActivityResult(requestCode, resultCode, data);

        if(requestCode == 1){
            if(resultCode == RESULT_OK){
                String addName = data.getStringExtra("Name");
                String addPrice = data.getStringExtra("Price");
                String addAmmount = data.getStringExtra("Ammount");
                boolean pressed = data.getBooleanExtra("Pressed", FALSE);

                int ammount = Integer.parseInt(addAmmount);
                int currentprice = Integer.parseInt(addPrice);
                int intval = ammount * currentprice;

                portfoliolist.add(new PortfolioItem(addName, ammount, intval, 0, 0, 0));

                GetPrice();
            }
            if(resultCode == RESULT_CANCELED){

            }
        }
    }

    private void GetPrice(){

        OkHttpClient client = new OkHttpClient();

        String url = "https://api.coinmarketcap.com/v1/ticker/";

        Request request = new Request.Builder().url(url).build();

        client.newCall(request).enqueue(new Callback() {
            @Override
            public void onFailure(Call call, IOException e) {
                e.printStackTrace();
            }

            @Override
            public void onResponse(Call call, Response response) throws IOException {
                if (response.isSuccessful()) {

                    final String myResponce = response.body().string();

                    globalCoin.clear();

                    try {
                        JSONArray coins = new JSONArray(myResponce);
                        for(int i = 0; i < coins.length(); i++){
                            try {
                                JSONObject coin = coins.getJSONObject(i);
                                String name = coin.getString("name");
                                String price = coin.getString("price_usd");
                                String change = coin.getString("percent_change_24h");

                                globalCoin.add(new Coin(name, price, change));
                            } catch (JSONException e) {
                                e.printStackTrace();
                            }
                        }
                    } catch (JSONException e) {
                        e.printStackTrace();
                    }
                }
            }
        });

        for(int i = 0; i < globalCoin.size(); i++){
            for(int ii = 0; ii < portfoliolist.size(); ii++){
                if(globalCoin.get(i).getName() == portfoliolist.get(ii).name){
                    int gottenprice = Integer.parseInt(globalCoin.get(i).getPrice());
                    portfoliolist.get(ii).price = gottenprice;
                    portfoliolist.get(ii).curvalue = portfoliolist.get(ii).price * portfoliolist.get(ii).ammount;
                    portfoliolist.get(ii).change = portfoliolist.get(ii).curvalue / portfoliolist.get(ii).intvalue - 1;
                }
            }
        }

    }

编辑：logcat日志：

＆＃13;

05-05 18:26:33.121 28991-28991/com.example.vartotojas.heycrypto E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.vartotojas.heycrypto, PID: 28991
    java.lang.RuntimeException: Failure delivering result ResultInfo{who=null, request=1, result=-1, data=Intent { (has extras) }} to activity {com.example.vartotojas.heycrypto/com.example.vartotojas.heycrypto.PortfolioActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'boolean java.util.ArrayList.add(java.lang.Object)' on a null object reference
        at android.app.ActivityThread.deliverResults(ActivityThread.java:4268)
        at android.app.ActivityThread.handleSendResult(ActivityThread.java:4312)
        at android.app.ActivityThread.-wrap19(Unknown Source:0)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1644)
        at android.os.Handler.dispatchMessage(Handler.java:106)
        at android.os.Looper.loop(Looper.java:164)
        at android.app.ActivityThread.main(ActivityThread.java:6494)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:438)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:807)
     Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'boolean java.util.ArrayList.add(java.lang.Object)' on a null object reference
        at com.example.vartotojas.heycrypto.PortfolioActivity.onActivityResult(PortfolioActivity.java:113)
        at android.app.Activity.dispatchActivityResult(Activity.java:7276)
        at android.app.ActivityThread.deliverResults(ActivityThread.java:4264)
        at android.app.ActivityThread.handleSendResult(ActivityThread.java:4312) 
        at android.app.ActivityThread.-wrap19(Unknown Source:0) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1644) 
        at android.os.Handler.dispatchMessage(Handler.java:106) 
        at android.os.Looper.loop(Looper.java:164) 
        at android.app.ActivityThread.main(ActivityThread.java:6494) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:438) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:807)

＆＃13;

Answer 1

这是由NullPointerException引起的。在添加项目之前初始化您的portfolioList，如下所示：

portfolioList = new ArrayList<>();

Answer 2

正如您在java.util.ArrayList.add(java.lang.Object)' on a null object reference上看到的那样，您将获得空指针异常。可能组合词是空的。或者检查哪个其他列表为空

Answer 3

在OnActivityResult方法中，行：

portfoliolist.add(new PortfolioItem(addName, ammount, intval, 0, 0, 0));

显示错误。由于列表portfoliolist为null。您应该始终使用NullPointerException支票或if-else

检查try catch

if(portfoliolist != null){
    // add the item to list
}else{
    // first instantiate and then add item to list
}

Answer 4

您可以在java中使用对象而无需启动它。在您的代码中，您没有启动keyIsPressed并且您正在其中添加项目。

只需用ArrayList方法替换您的部分代码。

onActivityResult()

按下按钮后应用程序崩溃：FATAL EXCEPTION：main

4 个答案: