java.lang.NullPointerException 来自错 return null？

Question

当我调试我的测试代码时，我在这一行中遇到错误

        Bitmap bitmap = BitmapFactory.decodeByteArray(image, 0, image.length);

有错误 java.lang.NullPointerException 似乎 image 变空了

这是我获取图像的代码

public class OkHttpHandler extends AsyncTask<Void, Void, byte[]> {

    private final String IMAGE_URL = "http://bit.ly/1DU2Zka";

    OkHttpClient httpClient = new OkHttpClient();

    @Override
    protected byte[] doInBackground(Void... params) {
        Log.d("e", "dddddddddd");
        Log.d("e", IMAGE_URL);

        Request.Builder builder = new Request.Builder();
        builder.url(IMAGE_URL);

        Request request = builder.build();

        try {

            Response response = httpClient.newCall(request).execute();

            System.out.println(response);
            Log.d("e", "FFFFFF response");

            return response.body().bytes();
        } catch (Exception e) {
            Log.d("e", "rrrrrrr");
            e.printStackTrace();
            Log.d("e", "rrrrrrr");

        }

        return null;
    }
}

这是否正确 return null;？

像这样我在 mainactivity

中获取图像

    public void downloadImage() {
        OkHttpHandler handler = new OkHttpHandler();

        byte[] image = new byte[0];

        try {

            image = handler.execute().get();
            Log.d("e", "hhhh handler");
System.out.print(image);
            if (image != null && image.length > 0){
                Log.isLoggable("e",image.length);
                Log.d("e", "ddddddd entered the try");
                Bitmap bitmap = BitmapFactory.decodeByteArray(image, 0, image.length);
                imageView.setImageBitmap(bitmap);
  //              txtBytes.setText("Total bytes downloaded: " + image.length);
            }

        } catch (Exception e) {
            Log.d("e", "rrrrrr error");

            e.printStackTrace();
//            txtBytes.setText("Hmm sorry, something went wrong!");
        }

    }

为什么我得到 nullpointerexception？

logcat

10-11 16:55:22.724  27814-27814/com.justedhak.www.i D/e﹕ ddddddd entered the try
10-11 16:55:22.739  27814-27814/com.justedhak.www.i D/e﹕ rrrrrr error
10-11 16:55:22.739  27814-27814/com.justedhak.www.i W/System.err﹕ java.lang.NullPointerException
10-11 16:55:22.739  27814-27814/com.justedhak.www.i W/System.err﹕ at com.justedhak.www.i.MainActivity.downloadImage(MainActivity.java:82)
10-11 16:55:22.739  27814-27814/com.justedhak.www.i W/System.err﹕ at com.justedhak.www.i.MainActivity.onCreate(MainActivity.java:54)
10-11 16:55:22.744  27814-27814/com.justedhak.www.i W/System.err﹕ at android.app.Activity.performCreate(Activity.java:5389)
10-11 16:55:22.744  27814-27814/com.justedhak.www.i W/System.err﹕ at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1105)
10-11 16:55:22.744  27814-27814/com.justedhak.www.i W/System.err﹕ at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2256)
10-11 16:55:22.744  27814-27814/com.justedhak.www.i W/System.err﹕ at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2350)
10-11 16:55:22.744  27814-27814/com.justedhak.www.i W/System.err﹕ at android.app.ActivityThread.access0(ActivityThread.java:163)
10-11 16:55:22.744  27814-27814/com.justedhak.www.i W/System.err﹕ at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1257)
10-11 16:55:22.744  27814-27814/com.justedhak.www.i W/System.err﹕ at android.os.Handler.dispatchMessage(Handler.java:102)
10-11 16:55:22.744  27814-27814/com.justedhak.www.i W/System.err﹕ at android.os.Looper.loop(Looper.java:157)
10-11 16:55:22.744  27814-27814/com.justedhak.www.i W/System.err﹕ at android.app.ActivityThread.main(ActivityThread.java:5335)
10-11 16:55:22.744  27814-27814/com.justedhak.www.i W/System.err﹕ at java.lang.reflect.Method.invokeNative(Native Method)
10-11 16:55:22.744  27814-27814/com.justedhak.www.i W/System.err﹕ at java.lang.reflect.Method.invoke(Method.java:515)
10-11 16:55:22.744  27814-27814/com.justedhak.www.i W/System.err﹕ at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1265)
10-11 16:55:22.744  27814-27814/com.justedhak.www.i W/System.err﹕ at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1081)
10-11 16:55:22.744  27814-27814/com.justedhak.www.i W/System.err﹕ at dalvik.system.NativeStart.main(Native Method)

Answer 1

我猜问题出在你的主程序中图像的分配（在你进入try块之前）。你只保留一个字节，可以吗？

然后您尝试将图像传递给一个字节，这似乎会产生问题。也许 Java 只是把图片的第一个字节取到你的可变图像中。这就是为什么您通过了 if 条件，但如果您尝试创建位图却失败了。

祝你好运

Answer 2

空指针异常在您没有正确初始化某些东西时显示。检查 OnCreate 方法，您是否正确初始化了所有内容？

java.lang.NullPointerException 来自错 return null？

java.lang.NullPointerException from wrong return null?

android

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