java - 应用程序停止工作

Question

我正在尝试运行这个程序。在 logcat 或构建过程中没有显示任何错误。但是我的设备出现错误:

Unfortunately my app has stopped working.

我该如何克服这个问题？

//activity.xml

<RelativeLayout                                                                                                             xmlns:android="http://schemas.android.com/apk/res/android"
            xmlns:tools="http://schemas.android.com/tools"android:layout_width="match_parent"
            android:layout_height="match_parent" android:paddingLeft="@dimen/activity_horizontal_margin"
            android:paddingRight="@dimen/activity_horizontal_margin"
            android:paddingTop="@dimen/activity_vertical_margin"
            android:paddingBottom="@dimen/activity_vertical_margin" 
            tools:context=".MainActivity"
            android:background="#daf1ff">

        <LinearLayout
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:orientation="vertical">
            <TextView
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="USER REGISTRATION"
                android:textSize="30dp"
                android:layout_marginBottom="20dp"
                android:layout_marginLeft="22dp"
                android:textColor="#ed2d26"/>
            <LinearLayout
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_marginBottom="10dp">
                <TextView android:text="Name: "
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:textSize="30dp"
                    android:textColor="#fd7214"/>
                <EditText
                    android:layout_width="250dp"
                    android:layout_height="wrap_content" />
            </LinearLayout>
            <LinearLayout
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_marginBottom="10dp">
                <TextView android:text="Gender: "
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:textSize="30dp"
                    android:layout_marginRight="20dp"
                    android:textColor="#fd7214"/>
                <RadioButton
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:text="Male"
                    android:textColor="#a61f82"
                    android:textSize="20dp"
                    android:layout_marginLeft="10dp"/>
                <RadioButton
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:text="Female"
                    android:textColor="#a61f82"
                    android:textSize="20dp"/>
            </LinearLayout>
            <LinearLayout
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_marginBottom="10dp">
                <TextView android:text="Country: "
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:textSize="30dp"
                    android:textColor="#fd7214"
                    android:layout_marginRight="20dp"/>
                <Spinner
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:id="@+id/spinner1"
                    android:layout_marginTop="20dp">
                </Spinner>
            </LinearLayout>
            <LinearLayout
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_marginBottom="10dp">
                <TextView android:text="Address: "
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:textSize="30dp"
                    android:layout_marginRight="20dp"
                    android:textColor="#fd7214"/>
                <EditText
                    android:layout_width="250dp"
                    android:layout_height="wrap_content" />
            </LinearLayout>
            <LinearLayout
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_marginBottom="10dp">
                <TextView android:text="Phone No: +91 "
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:textSize="30dp"
                    android:textColor="#fd7214"
                    />
                <EditText
                    android:layout_width="150dp"
                    android:layout_height="wrap_content" />
            </LinearLayout>
            <LinearLayout
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_marginBottom="50dp">
                <TextView android:text="E-mail: "
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:textSize="30dp"
                    android:textColor="#fd7214"
                    />
                <EditText
                    android:layout_width="86dp"
                    android:layout_height="wrap_content" />
                <Spinner
                    android:layout_width="100dp"
                    android:layout_height="wrap_content"
                    android:id="@+id/spinner2"
                    android:layout_marginTop="20dp">
                </Spinner>
                <TextView
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:text=".com "
                    android:textSize="20dp"
                    android:textColor="#ff0080"/>
            </LinearLayout>
            <LinearLayout
                android:layout_width="wrap_content"
                android:layout_height="wrap_content">
                <Button
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:text="REGISTER"
                    android:textSize="25dp"
                    android:layout_marginRight="70dp"
                    android:id="@+id/register"/>
                <Button
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:text="CANCEL"
                    android:textSize="25dp"
                    android:id="@+id/cancel"/>
            </LinearLayout>

        </LinearLayout>

    </RelativeLayout>

//MainActivity.java

package com.example.sreelakshmi.myuser;

    import android.app.Activity;
    import android.support.v7.app.ActionBarActivity;
    import android.os.Bundle;
    import android.view.Menu;
    import android.view.MenuItem;
    import android.view.View;
    import android.widget.AdapterView;
    import android.widget.ArrayAdapter;
    import android.widget.Button;
    import android.widget.Spinner;
    import android.widget.Toast;


    public class MainActivity extends Activity implements      AdapterView.OnItemSelectedListener {

    String[] country=new String[]{"India","Japan","Canada","US","Others"};
    String[] mailid=new String[]{"@ gmail","@ yahoo","@ rediffmail","@ hotmail","@ godrej"};
    Spinner spin1=(Spinner)findViewById(R.id.spinner1);
    Spinner spin2=(Spinner)findViewById(R.id.spinner2);
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        ArrayAdapter a1=new ArrayAdapter(this,android.R.layout.simple_spinner_dropdown_item,country);
        a1.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
        spin1.setAdapter(a1);
        ArrayAdapter a2=new ArrayAdapter(this,android.R.layout.simple_spinner_dropdown_item,mailid);
        a2.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
        spin2.setAdapter(a2);
        Button b1=(Button)findViewById(R.id.register);
        Button b2=(Button)findViewById(R.id.cancel);
        b1.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Toast.makeText(getApplicationContext(),"Registration Successful!",Toast.LENGTH_LONG).show();
            }
        });
        b2.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                finish();
            }
        });
        spin1.setOnItemSelectedListener(this);
        spin2.setOnItemSelectedListener(this);
    }

    @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();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }

    @Override
    public void onItemSelected(AdapterView<?> arg0, View arg1, int arg2,
                               long arg3) {
        switch(arg0.getId()){
            case R.id.spinner1 :
                Toast.makeText(getApplicationContext(),country[arg2],Toast.LENGTH_LONG).show();
                break;
            case R.id.spinner2 :
                //Your Another Action Here.
                Toast.makeText(getApplicationContext(),mailid[arg2],Toast.LENGTH_LONG).show();
                break;
        }
    }

    @Override
    public void onNothingSelected(AdapterView<?> parent) {

    }
}

Answer 1

Spinner spin1=(Spinner)findViewById(R.id.spinner1);
Spinner spin2=(Spinner)findViewById(R.id.spinner2);

必须在 setContentView 之后的 onCreate 中，有两个原因

1. 您需要一个有效的上下文才能使用 findViewById
2. 如果没有 setContentView，您将无法找到小部件，因此调用 findViewById 是不必要的