如何解决“NullPointerException：null 不能转换为非 null 类型 android.graphics.Bitmap”？答案

【问题标题】：How can I solve "NullPointerException: null cannot be cast to non-null type android.graphics.Bitmap"?如何解决“NullPointerException：null 不能转换为非 null 类型 android.graphics.Bitmap”？
【发布时间】：2020-11-17 13:28:23
【问题描述】：

我一直在尝试遵循本教程：https://developer.android.com/training/camera/photobasics
我使用图像按钮，所以我打开相机并拍照，但是当我接受照片时它就崩溃了：

E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.bujess, PID: 15270
    java.lang.RuntimeException: Failure delivering result ResultInfo{who=null, request=1, result=-1, data=null} to activity {com.example.bujess/com.example.bujess.WritingActivity}: java.lang.NullPointerException: null cannot be cast to non-null type android.graphics.Bitmap
        at android.app.ActivityThread.deliverResults(ActivityThread.java:5097)
        at android.app.ActivityThread.handleSendResult(ActivityThread.java:5138)
        at android.app.servertransaction.ActivityResultItem.execute(ActivityResultItem.java:51)
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2147)
        at android.os.Handler.dispatchMessage(Handler.java:107)
        at android.os.Looper.loop(Looper.java:237)
        at android.app.ActivityThread.main(ActivityThread.java:7814)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1068)
     Caused by: java.lang.NullPointerException: null cannot be cast to non-null type android.graphics.Bitmap
        at com.example.bujess.WritingActivity.onActivityResult(WritingActivity.kt:61)
        at android.app.Activity.dispatchActivityResult(Activity.java:8292)
        at android.app.ActivityThread.deliverResults(ActivityThread.java:5090)
        at android.app.ActivityThread.handleSendResult(ActivityThread.java:5138) 
        at android.app.servertransaction.ActivityResultItem.execute(ActivityResultItem.java:51) 
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135) 
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2147) 
        at android.os.Handler.dispatchMessage(Handler.java:107) 
        at android.os.Looper.loop(Looper.java:237) 
        at android.app.ActivityThread.main(ActivityThread.java:7814) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1068)

最可疑的行是“at com.example.bujess.WritingActivity.onActivityResult(WritingActivity.kt:61)”。但这些是我从指南 onActivityResult 复制的行：

override fun onActivityResult(requestCode: Int, resultCode: Int, data: Intent?) {
        super.onActivityResult(requestCode, resultCode, data)
        if (requestCode == REQUEST_IMAGE_CAPTURE && resultCode == RESULT_OK) {
            val imageBitmap = data?.extras?.get("data") as Bitmap
            val imageView = findViewById<ImageView>(R.id.opGallNCam)
            imageView?.setImageBitmap(imageBitmap)
            galleryAddPic()
        }
    }

第 61 行是："val imageBitmap = data?.extras?.get("data") as Bitmap"
opGallNCam 是 ImageButton 的 ID 我是 Kotlin 的新手。提前谢谢你

【问题讨论】：

标签： android kotlin

【解决方案1】：

为了避免抛出异常，可以使用安全的转换运算符 as?失败时返回 null

val imageBitmap = data?.extras?.get("data") as? Bitmap

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【解决方案2】：

java.lang.NullPointerException: null cannot be cast to non-null type android.graphics.Bitmap

问题在于：data?.extras?.get("data") 返回一个null 值，而您正试图将这个null 转换为Bitmap

首先data?.extras?.get("data")不会给你返回Bitmap，但是你可以先用data?.data得到一个Uri对象，然后把它转换成一个Bitmap，如下图，把你的onActivityResult方法改成：

override fun onActivityResult(requestCode: Int, resultCode: Int, data: Intent?) {
    super.onActivityResult(requestCode, resultCode, data)
    if (requestCode == 10 && resultCode == RESULT_OK) {
        val imageUri = data?.data as Uri
        var imageBitmap: Bitmap
        
        val bitmap = if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.P) {
            imageBitmap = ImageDecoder.decodeBitmap(ImageDecoder.createSource(contentResolver, imageUri))
        } else {
            imageBitmap = MediaStore.Images.Media.getBitmap(contentResolver, imageUri)
        }
        
//............... rest of your code

Source of conversion

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