Question

我在尝试setImageResource到ImageView数组中的某些图像时，我有点困惑。我在一个更简单的项目中复制了错误，所以这里是代码。我确信这一定是一个愚蠢的错误，但我已经尝试了很多，无法弄清楚正确的执行。我无法理解为什么图像是一个空对象引用，因为我已经以我能想到的各种方式初始化它。我在代码中提到的行中收到此错误。

java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ImageView.setImageResource(int)' on a null object reference.

package com.example.test;

import android.media.Image;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.ImageView;

public class MainActivity extends AppCompatActivity {
private ImageView image1;
private ImageView image2;
private ImageView image3;
private ImageView image;
private ImageView[] images = {image1, image2, image3, image};
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    image1 =(ImageView) findViewById(R.id.image1);
    image2 = (ImageView) findViewById(R.id.image2);
    image3 = (ImageView) findViewById(R.id.image3);
    image = (ImageView) findViewById(R.id.image);

    setImages();

}

public void setImages() {
    //This is where I am getting the error
    images[0].setImageResource(R.drawable.a);
    images[1].setImageResource(R.drawable.b);
    images[2].setImageResource(R.drawable.c);
    images[3].setImageResource(R.drawable.d);
}

}

Answer 1

public class MainActivity extends AppCompatActivity {

private ImageView[] images = new ImageView[4];
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);

images [0]=(ImageView) findViewById(R.id.image1);
images [1] = (ImageView) findViewById(R.id.image2);
images [2] = (ImageView) findViewById(R.id.image3);
images [3] = (ImageView) findViewById(R.id.image);

setImages();

}

public void setImages() {
//This is where I am getting the error
images[0].setImageResource(R.drawable.a);
images[1].setImageResource(R.drawable.b);
images[2].setImageResource(R.drawable.c);
images[3].setImageResource(R.drawable.d);
}

Answer 2

当你创建了如下图像的数组

 private ImageView[] images;

在创建image1之前，image2就像它一样，它将始终返回null。

尝试使用以下代码。

private ImageView[] images = {image1, image2, image3, image};
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    image1 =(ImageView) findViewById(R.id.image1);
    image2 = (ImageView) findViewById(R.id.image2);
    image3 = (ImageView) findViewById(R.id.image3);
    image = (ImageView) findViewById(R.id.image);
   images = new ImageView[]{image1, image2, image3, image};
    setImages();

}

希望这些可以帮助你。

Answer 3

您需要在images方法中获取值后初始化onCreate数组，因为image1，image2，image3和image由于初始化器（用于图像的初始化器）在构造函数之前执行（并且肯定在null方法之前），因此在初始化图像时onCreate()为public class MainActivity extends AppCompatActivity { private ImageView image1; private ImageView image2; private ImageView image3; private ImageView image; private ImageView[] images; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); image1 =(ImageView) findViewById(R.id.image1); image2 = (ImageView) findViewById(R.id.image2); image3 = (ImageView) findViewById(R.id.image3); image = (ImageView) findViewById(R.id.image); images = new ImageView[4]; images[0] = image1; image[1] = image2; image[2] = image3; image[3] = image; setImages(); } public void setImages() { images[0].setImageResource(R.drawable.a); images[1].setImageResource(R.drawable.b); images[2].setImageResource(R.drawable.c); images[3].setImageResource(R.drawable.d); } }。请尝试以下方法，

core_url_rewrite.id_path LIKE 'category/%'

希望这有帮助

空的ImageView数组

3 个答案: