Android编辑画布上的文本

我有一个editText，我想在画布上绘制输入的内容，画布上有我的资源“ger”。 我做了一个简单的代码，但在我看来，它无法工作。IDK问题是什么，当我运行它时，它意外停止

这是我的班级代码 公共类StartActivity扩展活动{

/** Called when the activity is first created. */

static Bitmap bmp;
static EditText et;
static ImageView iv;

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);
    EditText et = (EditText) findViewById(R.id.editText1);
    ImageView iv = (ImageView) findViewById(R.id.imageView1);
    Bitmap bmp = Bitmap.createBitmap(et.getDrawingCache());
}
public void onDraw (Canvas canvas){

    try {
        canvas.drawColor (Color.BLACK) ;
        Bitmap ab = BitmapFactory.decodeResource(getResources(),(R.drawable.ger)) ;
        ab = bmp;

        canvas.drawBitmap ( ab , 0 , 0 , null ) ;

        Paint paint = new Paint();
        paint.setColor(Color.WHITE);
        canvas.drawText(et.toString(),10,10,paint);
        iv.setImageBitmap(bmp);

    } catch ( Exception e ) {
        e.printStackTrace ( ) ;
    } catch ( Error e ) {
        e.printStackTrace ( ) ;
    }

}
}

日志：

08-17 22:51:03.526: D/AndroidRuntime(509): Shutting down VM
08-17 22:51:03.526: W/dalvikvm(509): threadid=1: thread exiting with uncaught exception (group=0x40015560)
08-17 22:51:03.547: E/AndroidRuntime(509): FATAL EXCEPTION: main
08-17 22:51:03.547: E/AndroidRuntime(509): java.lang.RuntimeException: Unable to start activity ComponentInfo{example.edittext.com/example.edittext.com.StartActivity}: java.lang.NullPointerException
08-17 22:51:03.547: E/AndroidRuntime(509):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1647)
08-17 22:51:03.547: E/AndroidRuntime(509):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1663)
08-17 22:51:03.547: E/AndroidRuntime(509):  at android.app.ActivityThread.access$1500(ActivityThread.java:117)
08-17 22:51:03.547: E/AndroidRuntime(509):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:931)
08-17 22:51:03.547: E/AndroidRuntime(509):  at android.os.Handler.dispatchMessage(Handler.java:99)
08-17 22:51:03.547: E/AndroidRuntime(509):  at android.os.Looper.loop(Looper.java:123)
08-17 22:51:03.547: E/AndroidRuntime(509):  at android.app.ActivityThread.main(ActivityThread.java:3683)
08-17 22:51:03.547: E/AndroidRuntime(509):  at java.lang.reflect.Method.invokeNative(Native Method)
08-17 22:51:03.547: E/AndroidRuntime(509):  at java.lang.reflect.Method.invoke(Method.java:507)
08-17 22:51:03.547: E/AndroidRuntime(509):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
08-17 22:51:03.547: E/AndroidRuntime(509):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
08-17 22:51:03.547: E/AndroidRuntime(509):  at dalvik.system.NativeStart.main(Native Method)
08-17 22:51:03.547: E/AndroidRuntime(509): Caused by: java.lang.NullPointerException
08-17 22:51:03.547: E/AndroidRuntime(509):  at android.graphics.Bitmap.createBitmap(Bitmap.java:367)
08-17 22:51:03.547: E/AndroidRuntime(509):  at example.edittext.com.StartActivity.onCreate(StartActivity.java:27)
08-17 22:51:03.547: E/AndroidRuntime(509):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
08-17 22:51:03.547: E/AndroidRuntime(509):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1611)
08-17 22:51:03.547: E/AndroidRuntime(509):  ... 11 more

xml：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="vertical" >

    <EditText
        android:id="@+id/editText1"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:ems="10" >

        <requestFocus />
    </EditText>

    <ImageView
        android:id="@+id/imageView1"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_weight="0.17"
        android:src="@drawable/ger" />

</LinearLayout>

---

这里的问题是，您试图从缓存中创建一个

位图

。这不可能很顺利

你需要做的是这样的：

/** Called when the activity is first created. */

static Bitmap bmp;
static EditText et;
static ImageView iv;
static Canvas ivCanvas; // We'll be using our own Canvas.

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);
    EditText et = (EditText) findViewById(R.id.editText1);
    ImageView iv = (ImageView) findViewById(R.id.imageView1);

    // Move this up to onCreate
    Bitmap ab = BitmapFactory.decodeResource(getResources(),(R.drawable.ger)) ;
    bmp = convertToMutable(ab); // Initialize it here with the contents of ab. This effectively clones it and makes it mutable.
    ab = null; // Dispose of ab.

    ivCanvas = new Canvas(bmp); // Create our Canvas!

    // Add a TextWatcher
    et.addTextChangedListener(new TextWatcher() {
        public void onTextChanged(CharSequence s, int start, int before, int count) {
            updateCanvas(); // Call the canvas update
        }
        public void beforeTextChanged(CharSequence s, int start, int count, int after) {
        }
        public void afterTextChanged(Editable s) {
        }
    });
}
public void updateCanvas() {
    ivCanvas.drawColor (Color.BLACK) ;

    ivCanvas.drawBitmap ( bmp , 0 , 0 , null ) ;

    Paint paint = new Paint();
    paint.setColor(Color.WHITE);
    ivCanvas.drawText(et.getText().toString(),10,10,paint);

    // Everything has been drawn to bmp, so we can set that here, now.
    iv.setImageBitmap(bmp);

    // Removed the "catch" blocks so you can actually know when you're getting errors! Feel free to re-add later.
}

我已经对此进行了彻底的评论，以便您能够理解我所做的更改。我认为这里需要进一步的更改，但这至少对您现在来说是可行的

编辑：

我已将代码转换为在

TextWatcher

中使用。您可以从中找到有关基本实现的信息

编辑2：

---

您需要将

位图

转换为“可变”（可变）位图位图。您可以使用中找到的代码。我在上面添加了一个调用。

您可以发布LogCat错误输出吗？另外，您可以显示XML在

ger

的位置吗？为什么您要尝试捕捉

错误

？抱歉，看看更新的问题。.我现在发布XML谢谢Eric，但我从中得到一个错误。onDraw方法onDraw（Canvas）未定义类型ActivityYeah，我想你会的。我已经更新了我的答案以使用

TextWatcher

实现。谢谢你Eric，但现在我正在删除@override annotations错误，顺便说一句，accepted=）如果

TextWatcher

给你带来错误，你可以安全地删除

TextWatcher

的

@Override

s