获取 java.lang.NullPointerException 从字符串数组或列表或 xml 文件简单地填充微调器(strings.xml)
Getting java.lang.NullPointerException On simply populating spinner from string array or list or xml file(strings.xml)
我想通过字符串数组或通过 XML 文件 (strings.xml) 填充 spinner。但是我收到 java.lang.NullPointerException:
错误。我在 google 上搜索了很多,但毫无价值。我试过的如下。
SecondActivity.java
package com.example.android02.personalityinsight;
import android.os.Bundle;
import android.support.design.widget.TabLayout;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentStatePagerAdapter;
import android.support.v4.view.ViewPager;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.Spinner;
public class SecondActivity extends AppCompatActivity implements View.OnClickListener {
TabLayout tabs;
ViewPager viewPager;
MyPagerAdapter pagerAdapter;
Spinner sp1, sp2;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_second);
// String colors[] = {"Red", "Blue", "White", "Yellow", "Black", "Green", "Purple", "Orange", "Grey"};
// sp1 = (Spinner) findViewById(R.id.sp1);
//
// ArrayAdapter<String> spinnerArrayAdapter = new ArrayAdapter<String>(this, android.R.layout.simple_spinner_item, colors);
// spinnerArrayAdapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
// sp1.setAdapter(spinnerArrayAdapter);
sp2 = (Spinner) findViewById(R.id.sp2);
ArrayAdapter<CharSequence> adapter = ArrayAdapter.createFromResource(
this, R.array.ans, android.R.layout.simple_spinner_item);
adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
sp2.setAdapter(adapter);
tabs = (TabLayout) findViewById(R.id.tabs);
viewPager = (ViewPager) findViewById(R.id.viewPager);
submit = (Button) findViewById(R.id.btn_submit);
tabs.addTab(tabs.newTab().setText("Personality Insights"));
tabs.addTab(tabs.newTab().setText("Quiz"));
tabs.addTab(tabs.newTab().setText("PI v/s Quiz"));
pagerAdapter = new MyPagerAdapter(getSupportFragmentManager(), tabs.getTabCount());
viewPager.setAdapter(pagerAdapter);
tabs.setTabsFromPagerAdapter(pagerAdapter);
tabs.setupWithViewPager(viewPager);
}
@Override
public void onClick(View v) {
switch (v.getId()) {
case R.id.btn_submit:
break;
default:
}
}
private class MyPagerAdapter extends FragmentStatePagerAdapter {
int mNumOfTabs;
public MyPagerAdapter(FragmentManager fm, int mNumOfTabs) {
super(fm);
this.mNumOfTabs = mNumOfTabs;
}
public MyPagerAdapter(FragmentManager fm) {
super(fm);
}
@Override
public Fragment getItem(int position) {
switch (position) {
case 0:
return TabOne_Fragment.newInstance();
case 1:
return TanTwo_Fragment.newInstance();
case 2:
return TabThree_Fragment.newInstance();
default:
return TabOne_Fragment.newInstance();
}
}
@Override
public int getCount() {
return mNumOfTabs;
}
}
}
tabtwo_fragment.xml
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
android:padding="10dp">
<TableLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:gravity="center_horizontal">
<TableRow
android:id="@+id/row1"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:gravity="center_vertical">
<TextView
android:id="@+id/q1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:gravity="center"
android:padding="6dp"
android:text="Sitting and reading: "
android:textAppearance="?android:attr/textAppearance" />
<Spinner
android:id="@+id/sp1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"></Spinner>
</TableRow>
<TableRow
android:id="@+id/row2"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:gravity="center_vertical">
<TextView
android:id="@+id/q2"
android:layout_width="250dp"
android:layout_height="wrap_content"
android:gravity="center"
android:padding="6dp"
android:text="Sitting, inactive in a public place (e.g. a theatre or a meeting): "
android:textAppearance="?android:attr/textAppearance" />
<Spinner
android:id="@+id/sp2"
android:layout_width="wrap_content"
android:layout_height="wrap_content"></Spinner>
</TableRow>
</TableLayout>
</RelativeLayout>
strings.xml
<resources>
<string name="app_name">PersonalityInsight</string>
<!-- Custom -->
<string name="facebook_app_id">XXXXXXXXXXXXXXXX</string>
<string-array name="ans">
<item>Zero</item>
<item>One</item>
<item>Two</item>
<item>Three</item>
</string-array>
</resources>
然而,无论我是从 ARRAY 还是从 XML[= 填充微调器,我都在这一行 sp2.setAdapter(adapter);
收到错误36=] 文件。我也尝试用 List 填充微调器,但发生了同样的错误。
提前致谢。
错误提示您的适配器为空。
尝试更改您的适配器,像这样初始化您的适配器:
ArrayAdapter<CharSequence> adapter =
new ArrayAdapter<CharSequence>(this, android.R.layout.simple_spinner_item, R.array.ans);
编辑
其实你知道的,为什么不在你的 xml 文件中这样做,就像这样:
<Spinner
android:id="@+id/sp1"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:spinnerMode="dropdown"
android:entries="@array/ans"
android:prompt="@string/select_one"/>
EDIT2
由于您更喜欢以编程方式执行此操作,请尝试:
ArrayAdapter<String> adapter = new ArrayAdapter<String>(this, android.R.layout.simple_spinner_item, getResources().getStringArray(R.array.ans));
adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
sp2.setAdapter(adapter);
R.array.ans
改为 getResources().getStringArray(R.array.ans)
希望对您有所帮助。
由于您在 Fragment 中创建了 Spinner,因此当您尝试通过 findViewById()
在 activity 中找到 Spinner s1/s2 时,它不存在,这就是 NPE 抛出的内容.
所以我认为您应该改为在 Fragment onCreateView()
中填充 Spinner。
你可以这样做:Error populating spinner in a fragment
步骤 1 --> 将数组添加到 string.xml 文件
例如
<string-array name="ans">
<item>Zero</item>
<item>One</item>
<item>Two</item>
<item>Three</item>
</string-array>
步骤 2 将此数组添加到微调器 xml
android:entries="@array/ans"
步骤 3 在您的 java 文件中
Spinner spinner = new Spinner(this);
ArrayAdapter<String> spinnerArrayAdapter = new ArrayAdapter<String>(this, android.R.layout.simple_spinner_item, spinnerArray); //selected item will look like a spinner set from XML
spinnerArrayAdapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
spinner.setAdapter(spinnerArrayAdapter);
我想通过字符串数组或通过 XML 文件 (strings.xml) 填充 spinner。但是我收到 java.lang.NullPointerException:
错误。我在 google 上搜索了很多,但毫无价值。我试过的如下。
SecondActivity.java
package com.example.android02.personalityinsight;
import android.os.Bundle;
import android.support.design.widget.TabLayout;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentStatePagerAdapter;
import android.support.v4.view.ViewPager;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.Spinner;
public class SecondActivity extends AppCompatActivity implements View.OnClickListener {
TabLayout tabs;
ViewPager viewPager;
MyPagerAdapter pagerAdapter;
Spinner sp1, sp2;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_second);
// String colors[] = {"Red", "Blue", "White", "Yellow", "Black", "Green", "Purple", "Orange", "Grey"};
// sp1 = (Spinner) findViewById(R.id.sp1);
//
// ArrayAdapter<String> spinnerArrayAdapter = new ArrayAdapter<String>(this, android.R.layout.simple_spinner_item, colors);
// spinnerArrayAdapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
// sp1.setAdapter(spinnerArrayAdapter);
sp2 = (Spinner) findViewById(R.id.sp2);
ArrayAdapter<CharSequence> adapter = ArrayAdapter.createFromResource(
this, R.array.ans, android.R.layout.simple_spinner_item);
adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
sp2.setAdapter(adapter);
tabs = (TabLayout) findViewById(R.id.tabs);
viewPager = (ViewPager) findViewById(R.id.viewPager);
submit = (Button) findViewById(R.id.btn_submit);
tabs.addTab(tabs.newTab().setText("Personality Insights"));
tabs.addTab(tabs.newTab().setText("Quiz"));
tabs.addTab(tabs.newTab().setText("PI v/s Quiz"));
pagerAdapter = new MyPagerAdapter(getSupportFragmentManager(), tabs.getTabCount());
viewPager.setAdapter(pagerAdapter);
tabs.setTabsFromPagerAdapter(pagerAdapter);
tabs.setupWithViewPager(viewPager);
}
@Override
public void onClick(View v) {
switch (v.getId()) {
case R.id.btn_submit:
break;
default:
}
}
private class MyPagerAdapter extends FragmentStatePagerAdapter {
int mNumOfTabs;
public MyPagerAdapter(FragmentManager fm, int mNumOfTabs) {
super(fm);
this.mNumOfTabs = mNumOfTabs;
}
public MyPagerAdapter(FragmentManager fm) {
super(fm);
}
@Override
public Fragment getItem(int position) {
switch (position) {
case 0:
return TabOne_Fragment.newInstance();
case 1:
return TanTwo_Fragment.newInstance();
case 2:
return TabThree_Fragment.newInstance();
default:
return TabOne_Fragment.newInstance();
}
}
@Override
public int getCount() {
return mNumOfTabs;
}
}
}
tabtwo_fragment.xml
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
android:padding="10dp">
<TableLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:gravity="center_horizontal">
<TableRow
android:id="@+id/row1"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:gravity="center_vertical">
<TextView
android:id="@+id/q1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:gravity="center"
android:padding="6dp"
android:text="Sitting and reading: "
android:textAppearance="?android:attr/textAppearance" />
<Spinner
android:id="@+id/sp1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"></Spinner>
</TableRow>
<TableRow
android:id="@+id/row2"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:gravity="center_vertical">
<TextView
android:id="@+id/q2"
android:layout_width="250dp"
android:layout_height="wrap_content"
android:gravity="center"
android:padding="6dp"
android:text="Sitting, inactive in a public place (e.g. a theatre or a meeting): "
android:textAppearance="?android:attr/textAppearance" />
<Spinner
android:id="@+id/sp2"
android:layout_width="wrap_content"
android:layout_height="wrap_content"></Spinner>
</TableRow>
</TableLayout>
</RelativeLayout>
strings.xml
<resources>
<string name="app_name">PersonalityInsight</string>
<!-- Custom -->
<string name="facebook_app_id">XXXXXXXXXXXXXXXX</string>
<string-array name="ans">
<item>Zero</item>
<item>One</item>
<item>Two</item>
<item>Three</item>
</string-array>
</resources>
然而,无论我是从 ARRAY 还是从 XML[= 填充微调器,我都在这一行 sp2.setAdapter(adapter);
收到错误36=] 文件。我也尝试用 List 填充微调器,但发生了同样的错误。
提前致谢。
错误提示您的适配器为空。
尝试更改您的适配器,像这样初始化您的适配器:
ArrayAdapter<CharSequence> adapter =
new ArrayAdapter<CharSequence>(this, android.R.layout.simple_spinner_item, R.array.ans);
编辑
其实你知道的,为什么不在你的 xml 文件中这样做,就像这样:
<Spinner
android:id="@+id/sp1"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:spinnerMode="dropdown"
android:entries="@array/ans"
android:prompt="@string/select_one"/>
EDIT2
由于您更喜欢以编程方式执行此操作,请尝试:
ArrayAdapter<String> adapter = new ArrayAdapter<String>(this, android.R.layout.simple_spinner_item, getResources().getStringArray(R.array.ans));
adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
sp2.setAdapter(adapter);
R.array.ans
改为getResources().getStringArray(R.array.ans)
希望对您有所帮助。
由于您在 Fragment 中创建了 Spinner,因此当您尝试通过 findViewById()
在 activity 中找到 Spinner s1/s2 时,它不存在,这就是 NPE 抛出的内容.
所以我认为您应该改为在 Fragment onCreateView()
中填充 Spinner。
你可以这样做:Error populating spinner in a fragment
步骤 1 --> 将数组添加到 string.xml 文件
例如
<string-array name="ans">
<item>Zero</item>
<item>One</item>
<item>Two</item>
<item>Three</item>
</string-array>
步骤 2 将此数组添加到微调器 xml
android:entries="@array/ans"
步骤 3 在您的 java 文件中
Spinner spinner = new Spinner(this);
ArrayAdapter<String> spinnerArrayAdapter = new ArrayAdapter<String>(this, android.R.layout.simple_spinner_item, spinnerArray); //selected item will look like a spinner set from XML
spinnerArrayAdapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
spinner.setAdapter(spinnerArrayAdapter);