Question

我想从我的移动存储中将图片加载到应用的图像视图中。可以肯定的是，我将图像保存在内部和外部存储中。但是在编译时，我得到一个空指针异常。我还将相同的图像放在drawable文件夹中，并尝试从那里设置imageview。但面临同样的问题。有人能帮我一下吗！。我正在添加我尝试过的代码片段。

方法-1：

File imageFile = new File(Environment.getExternalStorageDirectory(),"golden_eagle.jpg");
if(imageFile.exists()) {
    Log.v(LOGTAG, "Image file exists");
    BitmapFactory.Options options = new BitmapFactory.Options();
    options.inPreferredConfig = Bitmap.Config.ARGB_8888;
    Bitmap outputImageBitmap = BitmapFactory.decodeFile(imageFile.getAbsolutePath(), options);
    ImageView imageView = (ImageView)findViewById(R.id.sample_image);
    imageView.setImageBitmap(outputImageBitmap);
}

方法-2：

Bitmap bitimage;
bitimage = BitmapFactory.decodeResource(getResources(), R.drawable.golden_eagle);
if(bitimage == null)
Log.v(LOGTAG,"bitimage is empty");
else
Log.v(LOGTAG,"bitimage is not empty");
ImageView imageView = (ImageView)findViewById(R.id.sample_image);
imageView.setImageBitmap(bitimage);

方法-3：

ImageView imageView = (ImageView)findViewById(R.id.sample_image);
int resid = getResources().getIdentifier("golden_eagle","drawable",getPackageName());
imageView.setImageResource(resid);
//imageView.setImageResource(R.drawable.golden_eagle);

方法4：

//Some class extending AppCompatActivity
asyncTask.execute();

//some asyncTask

onpostExecute(){
    //Method:1
    //Method:2
    //Method:3
}

以上所有方法都以相同的编译错误结束

12-24 20:16:42.520 1349-1349/? E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.home.BequestProto, PID: 1349
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.home.BequestProto/com.example.home.BequestProto.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ImageView.setImageResource(int)' on a null object reference
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2585)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2667)
    at android.app.ActivityThread.-wrap11(ActivityThread.java)
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1494)
    at android.os.Handler.dispatchMessage(Handler.java:111)
    at android.os.Looper.loop(Looper.java:207)
    at android.app.ActivityThread.main(ActivityThread.java:5776)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:789)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:679)
    Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ImageView.setImageResource(int)' on a null object reference
    at com.example.home.BequestProto.MainActivity.onCreate(MainActivity.java:75)
    at android.app.Activity.performCreate(Activity.java:6582)
    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1113)
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2532)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2667) 
    at android.app.ActivityThread.-wrap11(ActivityThread.java) 
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1494) 
    at android.os.Handler.dispatchMessage(Handler.java:111) 
    at android.os.Looper.loop(Looper.java:207) 
    at android.app.ActivityThread.main(ActivityThread.java:5776) 
    at java.lang.reflect.Method.invoke(Native Method) 
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:789) 
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:679)

错误发生在我将图像设置为imageview的行。我知道它是一个空指针异常，因为有些地方我忘了初始化所需的对象。我想知道哪一个。

Answer 1

＆＃34;方法4：＆＃34;显示您正在使用异步任务执行。我想布局发生了变化，并试图在之后设置图像。

    ImageView imageView = (ImageView)findViewById(R.id.sample_image);
    if (imageView != null)
            imageView.setImageBitmap(outputImageBitmap);

仅当View存在时才会设置图像

Answer 2

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

这似乎来自“方法-3”，您正在呼叫setImageResource()。

此错误表示此行是问题所在：

ImageView imageView = (ImageView)findViewById(R.id.sample_image);

在所有四种情况下，

imageView都是null，因为findViewById()无法找到此小部件。

Answer 3

仔细检查ImageView是否为sample_image。在您的布局中找不到它

在ImageView中设置Bitmap时出现NullPointer异常

3 个答案: