[打开活动时应用程序崩溃

问题描述 投票：0回答：2

打开活动时我的应用程序崩溃。

活动代码命名为意大利面

package com.example.cook4u;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import android.widget.SearchView;
import android.content.Intent;



public class Pasta extends AppCompatActivity {

SearchView mysearchview3 = findViewById(R.id.searchView3);
String[] items = new String[]{"Masala pasta", "White sauce pasta", "Penne Alla Vodka", "Pasta 
Pomodoro", "Red Sauce Pasta", "Cheesezy Pasta", "Ravioli with Tomato Sauce", "Spaghetti Grilled 
Green Beans with Mushrooms", "Cheesy Shells and Greens", "Mac and Cheese", "5- Ingredient Pasta", 
"Creamy Cheddar Corn Pasta"};

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

    ListView listView = findViewById(R.id.listview3);
    final ArrayAdapter<String> adapter = new ArrayAdapter<String>(this, 
android.R.layout.simple_list_item_1, items);
    listView.setAdapter(adapter);
    listView.setOnItemClickListener(new OnItemClickListener() {
        @Override
        public void onItemClick(AdapterView<?> parent, View view, int position, long id) {

                if (position == 0) {
                    Intent myIntent;
                    myIntent = new Intent(Pasta.this,Masalapasta.class);
                    startActivity(myIntent);
                }
            if (position == 1) {
                Intent myIntent;
                myIntent = new Intent(Pasta.this,Whitesaucepasta.class);
                startActivity(myIntent);
            }
            if (position == 2) {
                Intent myIntent;
                myIntent = new Intent(Pasta.this,PenneAllaVodka.class);
                startActivity(myIntent);
            }
            if (position == 3) {
                Intent myIntent;
                myIntent = new Intent(Pasta.this,PastaPomodoro.class);
                startActivity(myIntent);
            }
            if (position == 4) {
                Intent myIntent;
                myIntent = new Intent(Pasta.this,RedSaucePasta.class);
                startActivity(myIntent);
            }
            if (position == 5) {
                Intent myIntent;
                myIntent = new Intent(Pasta.this,CheesezyPasta.class);
                startActivity(myIntent);
            }
            if (position == 6) {
                Intent myIntent;
                myIntent = new Intent(Pasta.this,Ravioli.class);
                startActivity(myIntent);
            }
            if (position == 7) {
                Intent myIntent;
                myIntent = new Intent(Pasta.this,Spaghetti.class);
                startActivity(myIntent);
            }
            if (position == 8) {
                Intent myIntent;
                myIntent = new Intent(Pasta.this,CheesyShellsandGreens.class);
                startActivity(myIntent);
            }
            if (position == 9) {
                Intent myIntent;
                myIntent = new Intent(Pasta.this,MacandCheese.class);
                startActivity(myIntent);
            }
            if (position == 10) {
                Intent myIntent;
                myIntent = new Intent(Pasta.this,IngredientPasta.class);
                startActivity(myIntent);
            }
            if (position == 11) {
                Intent myIntent;
                myIntent = new Intent(Pasta.this,CreamyCheddarCornPasta.class);
                startActivity(myIntent);
            }

        }
    });
    mysearchview3.setOnQueryTextListener(new SearchView.OnQueryTextListener() {
        @Override
        public boolean onQueryTextSubmit(String query) {
            return false;
        }

        @Override
        public boolean onQueryTextChange(String newText) {

            adapter.getFilter().filter(newText);
            return false;
        }
    });
}
}

导致活动崩溃的错误的错误

E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.cook4u, PID: 957
java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.cook4u/com.example.cook4u.Pasta}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.Window$Callback android.view.Window.getCallback()' on a null object reference
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2580)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2743)
    at android.app.ActivityThread.-wrap12(ActivityThread.java)
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1490)
    at android.os.Handler.dispatchMessage(Handler.java:102)
    at android.os.Looper.loop(Looper.java:154)
    at android.app.ActivityThread.main(ActivityThread.java:6165)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:888)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:778)
 Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 
  'android.view.Window$Callback android.view.Window.getCallback()' on a null object reference
    at android.support.v7.app.AppCompatDelegateImpl.<init>(AppCompatDelegateImpl.java:249)
    at android.support.v7.app.AppCompatDelegate.create(AppCompatDelegate.java:182)
    at android.support.v7.app.AppCompatActivity.getDelegate(AppCompatActivity.java:520)
    at android.support.v7.app.AppCompatActivity.findViewById(AppCompatActivity.java:191)
    at com.example.cook4u.Pasta.<init>(Pasta.java:17)
    at java.lang.Class.newInstance(Native Method)
    at android.app.Instrumentation.newActivity(Instrumentation.java:1100)
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2570)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2743) 
    at android.app.ActivityThread.-wrap12(ActivityThread.java) 
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1490) 
    at android.os.Handler.dispatchMessage(Handler.java:102) 
    at android.os.Looper.loop(Looper.java:154) 
    at android.app.ActivityThread.main(ActivityThread.java:6165) 
    at java.lang.reflect.Method.invoke(Native Method) 
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:888) 
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:778) 

[处理957终止。处理957终止。处理957终止。处理957终止。处理957终止。处理957终止。处理957终止。进程957终止。

谁能告诉我如何解决这个问题？

java android android-activity onitemclicklistener
2个回答
0
投票

替换：

SearchView mysearchview3 = findViewById(R.id.searchView3);

with：

SearchView mysearchview3;

然后，在onCreate()中，在setContentView(R.layout.activity_pasta);之后，添加：

mysearchview3 = findViewById(R.id.searchView3);

您无法成功调用findViewById()，直到调用了super.onCreate()后and该小部件将实际存在。该小部件将不存在，直到您单击setContentView()。

[关于Android应用程序开发的许多书籍和课程都涉及这种事情。

0
投票

您的onCreate函数上方的代码将它们放在onCreate（）中。这是因为仅当创建视图时才显示项目的ID。

public class Pasta extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_pasta);

SearchView mysearchview3 = findViewById(R.id.searchView3);
String[] items = new String[]{
"Masala pasta", 
"White sauce pasta", 
 "Penne Alla Vodka", 
"Pasta Pomodoro", 
"Red Sauce Pasta", 
"Cheesezy Pasta", 
"Ravioli with Tomato Sauce", 
"Spaghetti Grilled  Green Beans with Mushrooms", 
"Cheesy Shells and Greens", 
"Mac and Cheese", 
"5- Ingredient Pasta", 
"Creamy Cheddar Corn Pasta"};
}
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