单击意图时应用程序崩溃

Question

所以，如果这不是很明显，知道我是新手 我正在使用 Intent 打开一个新活动 (Main2Activity) 只要（Main2Activity）中没有任何事情发生，一切都会很好。

我在 Main2Activity 中做任何事情的那一刻它崩溃了，
例如：

import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.view.WindowManager;
import android.widget.Button;
import android.widget.CheckBox;
import butterknife.BindView;
import butterknife.ButterKnife;
import butterknife.OnClick;
public class MainActivity extends AppCompatActivity {
    @BindView(R.id.checkbox_diabetic)
    CheckBox diabetes;
    @BindView(R.id.firs_next_button)
    Button nextbutton;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        ButterKnife.bind(this);        getWindow().setSoftInputMode(WindowManager.LayoutParams.SOFT_INPUT_STATE_HIDDEN);
    }
    @OnClick(R.id.firs_next_button)
    public void setNextbutton(View view) {
        Intent intent = new Intent(MainActivity.this, Main2Activity.class);
        startActivity(intent);
    }
}

和：

package com.mhs.myapplication;

import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.CheckBox;

import butterknife.BindView;
import butterknife.OnClick;

public class Main2Activity extends AppCompatActivity {

    @BindView(R.id.diabetes_type_spinner)
    LabelledSpinner diabetestypes;
    @BindView(R.id.checkbox_diabetic)
    CheckBox diabetes;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main2);
        Intent intent = getIntent();
    }
}

它像魔术一样工作，活动打开没有任何问题。

但是，一旦我向 Main2activity 添加了一个东西，它就会在单击下一步按钮时崩溃。例如：

import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.CheckBox;
import butterknife.BindView;
import butterknife.OnClick;

public class Main2Activity extends AppCompatActivity {
    @BindView(R.id.diabetes_type_spinner)
    LabelledSpinner diabetestypes;
    @BindView(R.id.checkbox_diabetic)
    CheckBox diabetes;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main2);
        Intent intent = getIntent();

        diabetestypes.setItemsArray(R.array.diabetes_type_list);
    }
}

崩溃报告：

E/AndroidRuntime: FATAL EXCEPTION: main
                  Process: com.mhs.myapplication, PID: 27891
                  java.lang.RuntimeException: Unable to start activity ComponentInfo{com.mhs.myapplication/com.mhs.myapplication.Main2Activity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void com.mhs.myapplication.LabelledSpinner.setItemsArray(int)' on a null object reference
                      at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2484)
                      at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2544)
                      at android.app.ActivityThread.access$900(ActivityThread.java:150)
                      at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1394)
                      at android.os.Handler.dispatchMessage(Handler.java:102)
                      at android.os.Looper.loop(Looper.java:168)
                      at android.app.ActivityThread.main(ActivityThread.java:5845)
                      at java.lang.reflect.Method.invoke(Native Method)
                      at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:797)
                      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:687)
                   Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void com.mhs.myapplication.LabelledSpinner.setItemsArray(int)' on a null object reference
                      at com.mhs.myapplication.Main2Activity.onCreate(Main2Activity.java:22)
                      at android.app.Activity.performCreate(Activity.java:6248)
                      at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1125)
                      at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2437)
                      at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2544) 
                      at android.app.ActivityThread.access$900(ActivityThread.java:150) 
                      at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1394) 
                      at android.os.Handler.dispatchMessage(Handler.java:102) 
                      at android.os.Looper.loop(Looper.java:168) 
                      at android.app.ActivityThread.main(ActivityThread.java:5845) 
                      at java.lang.reflect.Method.invoke(Native Method) 
                      at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:797) 
                      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:687) 

Answer 1

Butter Knife 不会神奇地绑定视图。你必须添加

ButterKnife.bind(this);

也发送至Main2Activity。像这样：

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main2);
    ButterKnife.bind(this); // Need to add this!
    Intent intent = getIntent();
}

Answer 2

@tynn

所以而不是这样做

import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.CheckBox;
import butterknife.BindView;
import butterknife.OnClick;

public class Main2Activity extends AppCompatActivity {
    @BindView(R.id.diabetes_type_spinner)
    LabelledSpinner diabetestypes;
    @BindView(R.id.checkbox_diabetic)
    CheckBox diabetes;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main2);
        Intent intent = getIntent();

        diabetestypes.setItemsArray(R.array.diabetes_type_list);
    }
}

我做到了

package com.mhs.myapplication;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.view.WindowManager;
import android.widget.LinearLayout;

import butterknife.ButterKnife;


public class Main2Activity extends AppCompatActivity {



    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main2);


        LabelledSpinner diabetess_type = (LabelledSpinner) findViewById(R.id.diabetes_type_spinner);
        diabetess_type.setItemsArray(R.array.diabetes_type_list);
        diabetess_type.setColor(R.color.white);
        LinearLayout linearLayout = (LinearLayout) findViewById(R.id.diabetes_layout);
        linearLayout.setVisibility(View.GONE);
       getWindow().setSoftInputMode(WindowManager.LayoutParams.SOFT_INPUT_STATE_HIDDEN);
            ButterKnife.bind(this);

        }

    }

}

意外惊喜，它有效