Android应用程序，出现错误“java.lang.NullPointerException:println需要消息”

Question

我的应用程序有问题，我无法修复。我知道问题出在price=getIntent（）。getIntExtra（“价格”，-1）；但我不知道怎么修。我问过我的朋友，但他把我送到这里来了。请帮帮我，这是我的功课

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

    init();

    sqLiteHelper = new SQLiteHelper(this, "DrinDB.sqlite", null, 1);
    sqLiteHelper.queryData("CREATE TABLE IF NOT EXISTS CART(ID INTEGER PRIMARY KEY AUTOINCREMENT, name VARCHAR, " +
            "quantity INTEGER, price INTEGER)");

    btnAdd.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            if (item < 1) {
                Toast.makeText(DrinkDetailActivity.this, "Maaf Pesanan Minimal 1 cup", Toast.LENGTH_SHORT).show();
                return;
            }
            try {
                Log.i("TXT PRICE", txtName.getText().toString());
                sqLiteHelper.insertData(txtName.getText().toString().trim(),
                        txtQuantity.getText().toString().trim(),
                        txtPrice.getText().toString().trim());

                Toast.makeText(getApplicationContext(), "Masuk Keranjang!", Toast.LENGTH_SHORT).show();
                txtQuantity.setText("0");
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    });
    btnCart.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            Intent intent = new Intent(DrinkDetailActivity.this, CartListActivity.class);
            startActivity(intent);
        }
    });

    String name = getIntent().getStringExtra("name");
    String type = getIntent().getStringExtra("type");
    int image;
    image = getIntent().getIntExtra("image", -1);
    price = getIntent().getIntExtra("price", -1);
    Log.e("SECOND ACTIVITY", name);

    TextView nameTV = (TextView) findViewById(R.id.drink_name_text_view);
        nameTV.setText(name);
    TextView typeTV = (TextView) findViewById(R.id.type);
        typeTV.setText(type);
    ImageView imageV = (ImageView) findViewById(R.id.drink_image);
        imageV.setImageResource(image);
        imageV.setVisibility(View.VISIBLE);
    TextView priceTV = (TextView) findViewById(R.id.harga_detail_text_view);
        priceTV.setText(Integer.toString(price));

        sumTextView = (TextView) findViewById(R.id.sum_text_view);
        priceTotalTextView =(TextView) findViewById(R.id.harga_total_text_view);
        Button incrementBtn = (Button) findViewById(R.id.increment_btn);
        incrementBtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                increment();
            }
        });
        Button decrementBtn = (Button) findViewById(R.id.decrement_btn);
        decrementBtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                decrement();
            }
        });
}

private void init(){
    txtName = findViewById(R.id.drink_name_text_view);
    txtQuantity = findViewById(R.id.sum_text_view);
    txtPrice = findViewById(R.id.harga_total_text_view);
    btnAdd = findViewById(R.id.pesan_btn);
    btnCart = findViewById(R.id.cart_btn);
}
private void  increment(){
    item++;
    sumTextView.setText(Integer.toString(item));
    priceTotalTextView.setText(Integer.toString(sumOfProduct(price)));
}
private void decrement(){
    if(item<1){
        Toast.makeText(this, "maaf Anda tidak dapat memesan kurang dari 1", Toast.LENGTH_SHORT).show();
        return;
    }
    item =item-1;
    sumTextView.setText(Integer.toString(item));
    priceTotalTextView.setText(Integer.toString(sumOfProduct(price)));
}
private int sumOfProduct(int price){
    return item * price;
}

} `

错误消息在这里[com.dicoding.picodiploma.kedaikopi.Models.DrinkDetailActivity.onCreate（DrinkDetailActivity.java:69）]

at 安卓.app.ActivityThread.performLaunchActivity(ActivityThread.java:2760) at 安卓.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2821) at 安卓.app.ActivityThread.-wrap12(ActivityThread.java) at 安卓.app.ActivityThread$H.handleMessage(ActivityThread.java:1541) at 安卓.os.Handler.dispatchMessage(Handler.java:102) at 安卓.os.Looper.loop(Looper.java:181) at 安卓.app.ActivityThread.main(ActivityThread.java:6295) at java.lang.reflect.Method.invoke(Native Method) at com.安卓.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903) at com.安卓.internal.os.ZygoteInit.main(ZygoteInit.java:793) Caused by: java.lang.NullPointerException: println needs a message at 安卓.util.Log.println_native(Native Method) at 安卓.util.Log.e(Log.java:236) at com.dicoding.picodiploma.kedaikopi.Models.DrinkDetailActivity.onCreate(DrinkDetailActivity.java:69) at 安卓.app.Activity.performCreate(Activity.java:6834) at 安卓.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1125) at 安卓.app.ActivityThread.performLaunchActivity(ActivityThread.java:2713) at 安卓.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2821)  at 安卓.app.ActivityThread.-wrap12(ActivityThread.java)  at 安卓.app.ActivityThread$H.handleMessage(ActivityThread.java:1541)  at 安卓.os.Handler.dispatchMessage(Handler.java:102)  at 安卓.os.Looper.loop(Looper.java:181)  at 安卓.app.ActivityThread.main(ActivityThread.java:6295)  at java.lang.reflect.Method.invoke(Native Method)  at com.安卓.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)  at com.安卓.internal.os.ZygoteInit.main(ZygoteInit.java:793) 

Answer 1

使用Intent.putExtra时，需要指定名称（第一个参数）和值（第二个参数）。名称始终为String，必须以包名称作为前缀

从documentation开始：

The name must include a package prefix, for example the app com.android.contacts would use names like "com.android.contacts.ShowAll".

在您的示例中，当您创建启动活动的意图时，请使用intent.putExtra(getPackageName() + ".name", "my name")。当您想要提取额外的数据时，请使用String name = getIntent().getStringExtra(getPackageName() + ".name")