public class MainActivity extends ActionBarActivity implements OnClickListener {
Button btn;
ImageView view;
Bitmap bm;
Canvas canvas;
Paint paint;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
btn = (Button) super.findViewById(R.id.button1);
btn.setOnClickListener(this);
view = (ImageView) super.findViewById(R.id.imageView1);
Bitmap.Config conf = Bitmap.Config.ARGB_8888;
bm = Bitmap.createBitmap(200, 200, conf);
Canvas canvas = new Canvas(bm);
paint = new Paint(Paint.ANTI_ALIAS_FLAG);
paint.setColor(Color.BLACK);
canvas.drawCircle(50, 50, 10, paint);
view.setImageBitmap(bm);
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
try
{
// Start by customizing the error and warning services in Kakadu
Kdu_sysout_message sysout =
new Kdu_sysout_message(false); // Non-throwing message printer
Kdu_sysout_message syserr =
new Kdu_sysout_message(true); // Exception-throwing message printer
Kdu_message_formatter pretty_sysout =
new Kdu_message_formatter(sysout); // Non-throwing formatted printer
Kdu_message_formatter pretty_syserr =
new Kdu_message_formatter(syserr); // Throwing formatted printer
Kdu_global.Kdu_customize_warnings(pretty_sysout);
Kdu_global.Kdu_customize_errors(pretty_syserr);
Kdu_simple_file_source raw_src = null; // Must be disposed last
Jp2_family_src family_src = new Jp2_family_src(); // Dispose last
Jpx_source wrapped_src = new Jpx_source(); // Dispose before codestream
Kdu_codestream codestream = new Kdu_codestream(); // Needs `destroy'
Kdu_channel_mapping channels = new Kdu_channel_mapping();
Kdu_region_decompressor decompressor = new Kdu_region_decompressor();
try
{
// Open input file as raw codestream or a JP2/JPX file
String fname = Environment.getExternalStorageDirectory().getPath() + "/Android/CB.jp2";
family_src.Open(fname); // Generates an error if file doesn't exist
Jpx_layer_source xlayer = null;
Jpx_codestream_source xstream = null;
int success = wrapped_src.Open(family_src,true);
Kdu_compressed_source input=null; // Allows us to refer to compressed
// data source associated with either a raw codestream
// file or a JP2/JPX embedded codestream.
if (success < 0)
{ // Must open as raw file
family_src.Close();
wrapped_src.Close();
raw_src = new Kdu_simple_file_source(fname);
input = raw_src;
}
else
{ // Succeeded in opening as wrapped JP2/JPX source
xlayer = wrapped_src.Access_layer(0);
xstream = wrapped_src.Access_codestream(xlayer.Get_codestream_id(0));
input = xstream.Open_stream();
}
// Create the code-stream management machinery
codestream.Create(input);
if (xlayer != null)
channels.Configure(xlayer.Access_colour(0),xlayer.Access_channels(),
xstream.Get_codestream_id(),
xstream.Access_palette(),
xstream.Access_dimensions());
else
channels.Configure(codestream);
int ref_component = channels.Get_source_component(0);
Kdu_coords ref_expansion =
determine_reference_expansion(ref_component,channels,codestream);
// Determine dimensions for the rendered result & start decompressor
Kdu_dims view_dims =
decompressor.Get_rendered_image_dims(codestream,channels,-1,
0,ref_expansion,new Kdu_coords(1,1),
Kdu_global.KDU_WANT_OUTPUT_COMPONENTS);
Kdu_coords view_size = view_dims.Access_size();
// Note: changes in `view_size' will also affect `view_dims'
//start_display(view_size);
Kdu_coords display_size =
new Kdu_coords(200,200);
if (view_size.Get_x() > display_size.Get_x())
view_size.Set_x(display_size.Get_x());
if (view_size.Get_y() > display_size.Get_y())
view_size.Set_y(display_size.Get_y());
decompressor.Start(codestream,channels,-1,0,16384,view_dims,
ref_expansion,new Kdu_coords(1,1),false,
Kdu_global.KDU_WANT_OUTPUT_COMPONENTS);
// Render incrementally.
int region_buf_size = view_size.Get_x() * 60;
int[] region_buf = new int[region_buf_size];
Kdu_dims new_region = new Kdu_dims();
Kdu_dims incomplete_region = new Kdu_dims();
incomplete_region.Assign(view_dims);
while (decompressor.Process(region_buf,view_dims.Access_pos(),
0,0,region_buf_size,
incomplete_region,new_region))
{ // Transfer decompressed region into the main buffer
Kdu_coords offset =
new_region.Access_pos().Minus(view_dims.Access_pos());
Log.d("OFFSET", offset.Get_x() + "," + offset.Get_y());
Log.d("COLOR CODES", "" + region_buf[0] + region_buf[1] + region_buf[2] + region_buf[3]);
put_region(view_size.Get_x(),view_size.Get_y(),
new_region.Access_size().Get_x(),
new_region.Access_size().Get_y(),
offset.Get_x(),offset.Get_y(),region_buf);
}
decompressor.Finish();
//display.repaint();
}
catch (KduException e)
{ // See END NOTE 2
System.out.println("[Caught exception \"" + e.getMessage() +
"\" -- code " +
Integer.toHexString(e.Get_kdu_exception_code()) +
"]");
}
// Cleanup: Disposal must happen in the right order
// See END NOTE 3 for a discussion of Kakadu object disposal
decompressor.Native_destroy();
channels.Native_destroy();
if (codestream.Exists()) codestream.Destroy();
if (raw_src != null) raw_src.Native_destroy();
wrapped_src.Native_destroy();
family_src.Native_destroy();
}
catch (KduException e)
{ // See END NOTE 2
System.out.println("[Caught exception during creation of key objects!]");
}
}
private static Kdu_coords determine_reference_expansion(int reference_component, Kdu_channel_mapping channels, Kdu_codestream codestream) throws KduException{
int c;
Kdu_coords ref_subs = new Kdu_coords();
Kdu_coords subs = new Kdu_coords();
codestream.Get_subsampling(reference_component, ref_subs);
Kdu_coords min_subs = new Kdu_coords();
min_subs.Assign(ref_subs);
for(c = 0; c < channels.Get_num_channels(); c++){
codestream.Get_subsampling(channels.Get_source_component(c), subs);
if(subs.Get_x() < min_subs.Get_x())
min_subs.Set_x(subs.Get_x());
if (subs.Get_y() < min_subs.Get_y())
min_subs.Set_y(subs.Get_y());
}
Kdu_coords expansion = new Kdu_coords();
expansion.Set_x(ref_subs.Get_x() / min_subs.Get_x());
expansion.Set_y(ref_subs.Get_y() / min_subs.Get_y());
for (c=0; c < channels.Get_num_channels(); c++)
{
codestream.Get_subsampling(channels.Get_source_component(c),subs);
if ((((subs.Get_x() * expansion.Get_x()) % ref_subs.Get_x()) != 0) ||
(((subs.Get_y() * expansion.Get_y()) % ref_subs.Get_y()) != 0))
{
Kdu_global.Kdu_print_error(
"The supplied JP2 file contains colour channels " +
"whose sub-sampling factors are not integer " +
"multiples of one another.");
codestream.Apply_input_restrictions(0,1,0,0,null,
Kdu_global.KDU_WANT_OUTPUT_COMPONENTS);
channels.Configure(codestream);
expansion = new Kdu_coords(1,1);
}
}
return expansion;
}
class Kdu_sysout_message extends Kdu_message
{
public Kdu_sysout_message(boolean raise_exception)
{
this.raise_exception_on_end_of_message = raise_exception;
}
public void Put_text(String text)
{ // Implements the C++ callback function `kdu_message::put_text'
System.out.print(text);
}
public void Flush(boolean end_of_message) throws KduException
{ // Implements the C++ callback function `kdu_message::flush'.
if (end_of_message && raise_exception_on_end_of_message)
throw new KduException(Kdu_global.KDU_ERROR_EXCEPTION,
"In `Kdu_sysout_message'.");
}
private boolean raise_exception_on_end_of_message;
}
public void put_region(int view_width, int view_height, int reg_width, int reg_height, int reg_off_x, int reg_off_y, int[] reg_buf){
int[] img_buf;
if (bm == null){
img_buf = new int[view_width*view_height];
}
int dest_idx = reg_off_x + reg_off_y*view_width;
int src_idx = 0;
int extra_row_gap = view_width - reg_width;
int i, j;
for (j=0; j < reg_height; j++, dest_idx+=extra_row_gap){
for (i=0; i < reg_width; i++, src_idx++, dest_idx++){
//Log.d("Test", i + "," + "," + j + "," + reg_buf[src_idx]);
//bm.setPixel(i, j, Color.rgb(45, 127, 0));
paint.setColor(reg_buf[src_idx]);
Log.d("Paint", paint.toString());
canvas.drawPoint(i, j, paint);
}
}//for
}
}
reg_buf [src_idx]是颜色代码。
我想在图像视图上逐点动态地绘制画布。
但是我得到了一个错误，在最后一行，canvas.drawPoint（i，j，paint）;
我该如何解决这个问题？
LogCat错误：
06-30 13：16：34.991：E / AndroidRuntime（1517）：致命异常：主要
06-30 13：16：34.991：E / AndroidRuntime（1517）：进程：com.xxxx.xxxx，PID：1517
06-30 13：16：34.991：E / AndroidRuntime（1517）：java.lang.NullPointerException
06-30 13：16：34.991：E / AndroidRuntime（1517）：位于com.xxxx.xxxx.MainActivity.put_region（MainActivity.java:277）
06-30 13：16：34.991：E / AndroidRuntime（1517）：位于com.xxxx.xxxx.MainActivity.onClick（MainActivity.java:173）
06-30 13：16：34.991：E / AndroidRuntime（1517）：位于android.view.View.performClick（View.java:4626）
06-30 13：16：34.991：E / AndroidRuntime（1517）：在android.view.View $ PerformClick.run（View.java:19218）
06-30 13：16：34.991：E / AndroidRuntime（1517）：位于android.os.Handler.handleCallback（Handler.java:733）
06-30 13：16：34.991：E / AndroidRuntime（1517）：位于android.os.Handler.dispatchMessage（Handler.java:95）
06-30 13：16：34.991：E / AndroidRuntime（1517）：at android.os.Looper.loop（Looper.java:157）
06-30 13：16：34.991：E / AndroidRuntime（1517）：位于android.app.ActivityThread.main（ActivityThread.java:5350）
06-30 13：16：34.991：E / AndroidRuntime（1517）：at java.lang.reflect.Method.invokeNative（本机方法）
06-30 13：16：34.991：E / AndroidRuntime（1517）：at java.lang.reflect.Method.invoke（Method.java:515）
06-30 13：16：34.991：E / AndroidRuntime（1517）：at com.android.internal.os.ZygoteInit $ MethodAndArgsCaller.run（ZygoteInit.java:1265）
06-30 13：16：34.991：E / AndroidRuntime（1517）：at com.android.internal.os.ZygoteInit.main（ZygoteInit.java:1081）
06-30 13：16：34.991：E / AndroidRuntime（1517）：at dalvik.system.NativeStart.main（本机方法）
最佳答案
当您尝试引用未初始化的方法或对象成员时，抛出NullPointerException。让我们看一下抛出异常的行：
canvas.drawPoint(i, j, paint);
此处
null可能是什么？即使在
canvas中初始化了onCreate也可以为null。如果canvas是null，则需要对其进行初始化。i和j是在循环中初始化的数字，因此这些不是问题的根源。如果
paint为null，则在drawPoint内部可能会引发异常，但是，由于它的setColor没有引发NullPointerException，因此我们可以排除此异常。如您所见，
canvas是null。但是，如果在onCreate中初始化它，怎么可能呢？答案是：您没有初始化它。您已使用初始化了局部变量Canvas canvas = new Canvas(bm);
如果不声明它，则仅使用该对象的成员，则它不应引发异常。因此，您应该将行更改为
canvas = new Canvas(bm);
关于android - Canvas 逐点绘制，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/31135597/