Android - imageView.getDrawable() returns null

问题

I am stuck on this seemingly easy issue. What am I doing wrong ?

ImageView mImageView;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        mImageView = (ImageView)findViewById(R.id.control);
        ClipDrawable drawable = (ClipDrawable)mImageView.getDrawable();
        drawable.setLevel(10);

    }

The app crashes at drawable.setLevel(10) with a NullPointerException (drawable is null).

Here is my xml:

circle.xml

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android"
    android:shape="oval"
    android:innerRadius="50dp"
    >

    <solid
        android:color="#FFAAFF"/>

</shape>

clip.xml

<?xml version="1.0" encoding="utf-8"?>
<clip xmlns:android="http://schemas.android.com/apk/res/android"
    android:clipOrientation="horizontal"
    android:drawable="@drawable/circle"
    android:gravity="clip_horizontal"

/>

activity_main.xml

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent"
    android:layout_height="match_parent" android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    android:paddingBottom="@dimen/activity_vertical_margin" tools:context=".MainActivity">

    <ImageView
        android:id="@+id/image"
        android:layout_height="100dp"
        android:layout_width="100dp"
        android:background="@drawable/clip"
        android:layout_centerHorizontal="true"
        />

</RelativeLayout>

Please help me out here !

回答1:

You set the drawable to background attribute of 'src'.

android:background="@drawable/clip"

. So change yours activity_main.xml by replacing background attribute to src:

android:src="@drawable/clip"

Finally yours activity_main.xml will be:

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent"
android:layout_height="match_parent" android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
android:paddingBottom="@dimen/activity_vertical_margin" tools:context=".MainActivity">

<ImageView
    android:id="@+id/image"
    android:layout_height="100dp"
    android:layout_width="100dp"
    android:scr="@drawable/clip"
    android:layout_centerHorizontal="true"
    />

Or you can get yours drawable by calling method getBackground() which returns drawable that was set by attribute android:background

来源：https://stackoverflow.com/questions/32773228/android-imageview-getdrawable-returns-null

标签

android

android-imageview

android-drawable