android studio中带有setImageDrawable方法的NullPointerException [重复]
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【中文标题】android studio中带有setImageDrawable方法的NullPointerException [重复]【英文标题】：NullPointerException with setImageDrawable method in android studio [duplicate] 【发布时间】：2018-12-18 22:02:19 【问题描述】：我刚刚为一个项目启动了一个应用程序，我想为其设置一个进入滑块。除了页面点之外，我得到了一切工作，当 IntroSlider 活动（显示所有幻灯片的活动）启动时不显示页面点，并在尝试转到下一张幻灯片时使应用程序崩溃。我不明白是什么导致了错误，我将不胜感激。在 IntroSlider.java 中查找注释，它指定了 android Studio 所说的导致错误的行号。谢谢
IntoSlider.java：
package com.businessbrains.businessbrains.Activities;
import android.content.Intent;
import android.graphics.drawable.Drawable;
import android.os.Build;
import android.support.v4.content.ContextCompat;
import android.support.v4.view.ViewPager;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.view.ViewGroup;
import android.view.WindowManager;
import android.widget.Button;
import android.widget.ImageView;
import android.widget.LinearLayout;
import com.businessbrains.businessbrains.Adapters.SlidesAdapter;
import com.businessbrains.businessbrains.Internals.PreferenceManager;
import com.businessbrains.businessbrains.R;
public class IntroSlider extends AppCompatActivity implements View.OnClickListener
private ViewPager mPager;
private int[] layouts = R.layout.slide_welcome, R.layout.slide_account, R.layout.slide_selftest, R.layout.slide_mutliplayer;
private SlidesAdapter slidesAdapter;
private LinearLayout Dots_Layout;
private ImageView[] dots;
private Button skipBtn, nextBtn;
@Override
protected void onCreate(Bundle savedInstanceState)
super.onCreate(savedInstanceState);
if(new PreferenceManager(this).isSlidesEnabled())
loadLogin();
if(Build.VERSION.SDK_INT >= 19)
getWindow().addFlags(WindowManager.LayoutParams.FLAG_TRANSLUCENT_STATUS);
else
getWindow().clearFlags(WindowManager.LayoutParams.FLAG_TRANSLUCENT_STATUS);
setContentView(R.layout.activity_intro_slider);
mPager= (ViewPager) findViewById(R.id.viewPager);
slidesAdapter = new SlidesAdapter(layouts, this);
mPager.setAdapter(slidesAdapter);
Dots_Layout = findViewById(R.id.dotsLayout);
nextBtn = (Button) findViewById(R.id.nextBtn);
nextBtn.setOnClickListener(this);
skipBtn = (Button) findViewById(R.id.skipBtn);
skipBtn.setOnClickListener(this);
mPager.addOnPageChangeListener(new ViewPager.OnPageChangeListener()
@Override
public void onPageScrolled(int i, float v, int i1)
@Override
public void onPageSelected(int i)
createDots(i);
if(i==layouts.length-1)
nextBtn.setText("Start");
skipBtn.setVisibility(View.INVISIBLE);
else
nextBtn.setText("Next");
skipBtn.setVisibility(View.VISIBLE);
@Override
public void onPageScrollStateChanged(int i)
);
private void createDots(int current_position)
if(Dots_Layout!=null)
Dots_Layout.removeAllViews();
dots = new ImageView[layouts.length];
for(int i = 0; i < layouts.length; i++)
if(i==current_position)
dots[i].setImageDrawable((Drawable)ContextCompat.getDrawable(getApplicationContext(), R.drawable.accessory_active_dots));
else
dots[i].setImageDrawable((Drawable)(ContextCompat.getDrawable(getApplicationContext(), R.drawable.accessory_inactive_dots)));
//line which is causing the error
LinearLayout.LayoutParams params = new LinearLayout.LayoutParams(ViewGroup.LayoutParams.WRAP_CONTENT, ViewGroup.LayoutParams.WRAP_CONTENT);
params.setMargins(4,0,4,0);
Dots_Layout.addView(dots[i], params);
@Override
public void onClick(View view)
switch(view.getId())
case R.id.nextBtn:
loadNextSlide();
break;
case R.id.skipBtn:
loadLogin();
new PreferenceManager(this).writeDisableSlides();
break;
private void loadLogin()
startActivity(new Intent(this, LoginOptionsActivity.class));
finish();
private void loadNextSlide()
int nextslide = mPager.getCurrentItem() + 1;
if(nextslide < layouts.length)
mPager.setCurrentItem(nextslide);
else
loadLogin();
new PreferenceManager(this).writeDisableSlides();
对应的.xml，activity_into_slider.xml：
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_
android:layout_
tools:context=".Activities.IntroSlider">
<android.support.v4.view.ViewPager
android:layout_
android:layout_
android:id="@+id/viewPager"
/>
<View
android:layout_
android:layout_
android:alpha=".5"
android:layout_above="@+id/dotsLayout"
android:background="@android:color/white"
android:layout_marginBottom="15dp"
></View>
<LinearLayout
android:layout_
android:layout_
android:id="@+id/dotsLayout"
android:layout_centerHorizontal="true"
android:layout_alignParentBottom="true"
android:orientation="horizontal"
android:gravity="center"
android:layout_marginBottom="55sp"
/>
<Button
android:layout_
android:layout_
android:text="Skip"
android:textSize="16sp"
android:layout_alignParentBottom="true"
android:layout_alignParentLeft="true"
android:background="@android:color/transparent"
android:id="@+id/skipBtn"
android:layout_marginBottom="8dp"
android:textColor="@android:color/white"
/>
<Button
android:layout_
android:layout_
android:text="Next"
android:textSize="16sp"
android:layout_alignParentBottom="true"
android:layout_alignParentRight="true"
android:background="@android:color/transparent"
android:id="@+id/nextBtn"
android:layout_marginBottom="8dp"
android:textColor="@android:color/white"
/>
</RelativeLayout>
其中一张幻灯片：
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_
android:layout_
android:background="@color/colorSlide_welcome">
<ImageView
android:layout_
android:layout_
android:src="@drawable/ic_welcome"
android:layout_centerHorizontal="true"
android:scaleType="centerCrop"
android:layout_marginTop="150dp"
android:id="@+id/img"
android:tint="@android:color/black"
/>
<TextView
android:layout_
android:layout_
android:text="@string/slide1title"
android:textColor="@android:color/white"
android:textSize="30sp"
android:textStyle="bold"
android:layout_centerHorizontal="true"
android:layout_below="@+id/img"
android:layout_marginTop="12dp"
android:id="@+id/slidetitle"
/>
<TextView
android:layout_
android:layout_
android:text="@string/slide1desc"
android:textColor="@android:color/white"
android:textSize="18sp"
android:gravity="center_horizontal"
android:layout_below="@+id/slidetitle"
android:layout_marginTop="10dp"
android:id="@+id/slide_desc"
android:layout_marginRight="40sp"
android:layout_marginLeft="40sp"
/>
</RelativeLayout>
正在抛出的错误：
07-11 00:30:30.253 6010-6010/com.businessbrains.businessbrains E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.businessbrains.businessbrains, PID: 6010
java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ImageView.setImageDrawable(android.graphics.drawable.Drawable)' on a null object reference
at com.businessbrains.businessbrains.Activities.IntroSlider.createDots(IntroSlider.java:89)
at com.businessbrains.businessbrains.Activities.IntroSlider.access$000(IntroSlider.java:21)
at com.businessbrains.businessbrains.Activities.IntroSlider$1.onPageSelected(IntroSlider.java:62)
at android.support.v4.view.ViewPager.dispatchOnPageSelected(ViewPager.java:1947)
at android.support.v4.view.ViewPager.scrollToItem(ViewPager.java:686)
at android.support.v4.view.ViewPager.setCurrentItemInternal(ViewPager.java:670)
at android.support.v4.view.ViewPager.setCurrentItemInternal(ViewPager.java:631)
at android.support.v4.view.ViewPager.setCurrentItem(ViewPager.java:612)
at com.businessbrains.businessbrains.Activities.IntroSlider.loadNextSlide(IntroSlider.java:118)
at com.businessbrains.businessbrains.Activities.IntroSlider.onClick(IntroSlider.java:101)
at android.view.View.performClick(View.java:6256)
at android.view.View$PerformClick.run(View.java:24701)
at android.os.Handler.handleCallback(Handler.java:789)
at android.os.Handler.dispatchMessage(Handler.java:98)
at android.os.Looper.loop(Looper.java:164)
at android.app.ActivityThread.main(ActivityThread.java:6541)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:767)
accessory_active_dots.xml：
<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android"
android:shape="oval"
android:useLevel="true"
android:dither="true">
<size android: android:/>
<solid android:color="@color/active_dots"/>
</shape>
accessory_inactive_dots.xml：
<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android"
android:shape="oval"
android:useLevel="true"
android:dither="true">
<size android: android:/>
<solid android:color="@color/inactive_dots"/>
</shape>
【问题讨论】：
【参考方案1】：dots = new ImageView[layouts.length]; 创建一个大小为layouts.length 的数组，但该数组的所有元素均为空。
所以当你在dots[i] 上调用setImageDrawable(..) 时，你实际上是在一个空对象上调用setImageDrawable(..) 方法。
修复：在使用前用非空值初始化dots[i]（即dots[i] =）。例如，在对 dots[i] 调用 setImageDrawable(..) 之前执行 dots[i] = new ImageView()。
【讨论】：
真是天才！！谢谢！！！ 很高兴为您提供帮助！ :-)以上是关于android studio中带有setImageDrawable方法的NullPointerException [重复]的主要内容，如果未能解决你的问题，请参考以下文章
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