android - 在 Kotlin 中将位图保存为图像

Question

我想将位图保存为图像文件。我尝试了以下代码并得到了错误。

val dir = File("/tempfolder/")

if (!dir.exists()) {
    print("dir not exist");
    dir.mkdirs()
}

val output = File("tempfile.jpg")
var os: OutputStream? = null

os = FileOutputStream(output)

bitmap.compress(Bitmap.CompressFormat.JPEG, 100, os)

os.flush()
os.close()

错误:

E/MessageQueue-JNI: Exception in MessageQueue callback: handleReceiveCallback
E/MessageQueue-JNI: java.io.FileNotFoundException: tempfile.jpg (Read-only file system)
        at java.io.FileOutputStream.open0(Native Method)
        at java.io.FileOutputStream.open(FileOutputStream.java:287)
        at java.io.FileOutputStream.<init>(FileOutputStream.java:223)
        at java.io.FileOutputStream.<init>(FileOutputStream.java:171)
        at com.app.symbolrecogniser.CanV.touchUp(CanV.kt:190)
        at com.app.symbolrecogniser.CanV.onTouchEvent(CanV.kt:102)
        at android.view.View.dispatchTouchEvent(View.java:11776)
        at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2968)
        at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2657)
        at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2968)
        at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2657)
        at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2968)
        at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2657)
        at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2968)
        at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2657)
        at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2968)
        at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2657)
        at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2968)
        at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2657)
        at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2968)
        at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2657)
        at com.android.internal.policy.DecorView.superDispatchTouchEvent(DecorView.java:448)
        at com.android.internal.policy.PhoneWindow.superDispatchTouchEvent(PhoneWindow.java:1829)
        at android.app.Activity.dispatchTouchEvent(Activity.java:3307)
        at androidx.appcompat.view.WindowCallbackWrapper.dispatchTouchEvent(WindowCallbackWrapper.java:69)
        at com.android.internal.policy.DecorView.dispatchTouchEvent(DecorView.java:410)
        at android.view.View.dispatchPointerEvent(View.java:12015)
        at android.view.ViewRootImpl$ViewPostImeInputStage.processPointerEvent(ViewRootImpl.java:4795)
        at android.view.ViewRootImpl$ViewPostImeInputStage.onProcess(ViewRootImpl.java:4609)
        at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:4147)
        at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:4200)
        at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:4166)
        at android.view.ViewRootImpl$AsyncInputStage.forward(ViewRootImpl.java:4293)
        at android.view.ViewRootImpl$InputStage.apply(ViewRootImpl.java:4174)
        at android.view.ViewRootImpl$AsyncInputStage.apply(ViewRootImpl.java:4350)
        at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:4147)
        at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:4200)
        at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:4166)
        at android.view.ViewRootImpl$InputStage.apply(ViewRootImpl.java:4174)
        at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:4147)
        at android.view.ViewRootImpl.deliverInputEvent(ViewRootImpl.java:6661)
        at android.view.ViewRootImpl.doProcessInputEvents(ViewRootImpl.java:6635)
        at android.view.ViewRootImpl.enqueueInputEvent(ViewRootImpl.java:6596)
        at android.view.ViewRootImpl$WindowInputEventReceiver.onInputEvent(ViewRootImpl.java:6764)
        at android.view.InputEventReceiver.dispatchInputEvent(InputEventReceiver.java:186)
        at android.os.MessageQueue.nativePollOnce(Native Method)
        at android.os.MessageQueue.next(MessageQueue.java:325)
        at android.os.Looper.loop(Looper.java:142)
        at android.app.ActivityThread.main(ActivityThread.java:6494)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:438)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:807)```

Answer 1

你可能想要 Context#getDir 反而

Retrieve, creating if needed, a new directory in which the applicationcan place its own custom data files. You can use the returned Fileobject to create and access files in this directory. Note that filescreated through a File object will only be accessible by your ownapplication; you can only set the mode of the entire directory, not ofindividual files.

The returned path may change over time if the calling app is moved toan adopted storage device, so only relative paths should be persisted.

Apps require no extra permissions to read or write to the returnedpath, since this path lives in their private storage.

但是还有其他一些您可以访问，例如 getCacheDir (对于临时内容，当用户清除应用程序缓存或释放存储空间时会被删除)， getFilesDir (只是 getDir 在其中创建新文件夹的主文件夹，如果您实际上不需要单独的文件夹 - 在应用程序卸载时被删除)和 getExternalFilesDir (与 getFilesDir 相同，只是它在外部存储上，如果你想把东西放在那里)。这些都是只有您的应用可以访问的私有(private)存储空间