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AsyncTask
AsyncTask约定了在子线程中运行任务的抽象方法,开发人员能够在自己定义AsyncTask的实现类中重写该方法,
则AsyncTask在工作时会自己主动开启子线程运行相关代码
AsyncTask类的声明:
public abstract class AsyncTask<Param,Progress,Result>
Param 运行异步任务后,须要參数的数据类型
Progress 运行异步任务过程中。标识进度的数据类型
Result 运行异步任务后。须要返回的结果的数据类型
AsyncTask中的抽象方法: public abstract Result doInBackground(params... params)
让AsyncTask開始工作:
public final AsyncTask<params,Progress,Result> execute(params...params)
该方法被调用后。会自己主动开启子线程并调用dnInBackground()方法,该方法
必须在UI线程中调用
案例:
布局:
- <Button
- android:id="@+id/button1"
- android:layout_width="wrap_content"
- android:layout_height="wrap_content"
- android:layout_alignParentTop="true"
- android:layout_centerHorizontal="true"
- android:layout_marginTop="104dp"
- android:onClick="doAsyncTask"
- android:text="開始" />
MainActivity:
- public class MainActivity extends Activity {
- @Override
- protected void onCreate(Bundle savedInstanceState) {
- super.onCreate(savedInstanceState);
- setContentView(R.layout.activity_main);
- System.out.println("onCreate" + Thread.currentThread().getId());
- }
- public void doAsyncTask(View view){
- new InnerAsyncTask().execute("");
- }
- private class InnerAsyncTask extends AsyncTask<Object, Object, Object>{
- @Override
- protected Object doInBackground(Object... params) {
- for(int i = 0; i < 30;i++){
- System.out.println("InnerAsyncTask" + Thread.currentThread().getId());
- try {
- Thread.sleep(1000);
- } catch (InterruptedException e) {
- e.printStackTrace();
- }
- }
- return null;
- }
- }
- }
AsyncTask更新UI
AsyncTask约定了任务运行完成后的回调方法,该方法并非抽象的,开发人员能够选择性的实现。
protected void onPostExecute(Result result)
该方法是执行在主线程的方法
实例:
布局:
- <Button
- android:id="@+id/button1"
- android:layout_width="wrap_content"
- android:layout_height="wrap_content"
- android:layout_alignParentTop="true"
- android:layout_centerHorizontal="true"
- android:layout_marginTop="104dp"
- android:onClick="doAsyncTask"
- android:text="開始" />
- <ImageView
- android:id="@+id/imageView1"
- android:layout_width="wrap_content"
- android:layout_height="wrap_content"
- android:layout_below="@+id/button1"
- android:layout_centerHorizontal="true"
- android:layout_marginTop="22dp"
- android:src="@drawable/abs" />
MainActivity:
- public class MainActivity extends Activity {
- private ImageView image;
- @Override
- protected void onCreate(Bundle savedInstanceState) {
- super.onCreate(savedInstanceState);
- setContentView(R.layout.activity_main);
- image = (ImageView) findViewById(R.id.imageView1);
- // System.out.println("onCreate" + Thread.currentThread().getId());
- }
- public void doAsyncTask(View view){
- new InnerAsyncTask().execute("");
- }
- private class InnerAsyncTask extends AsyncTask<String,Integer, Bitmap>{
- @Override
- protected Bitmap doInBackground(String... params) {
- try {
- Thread.sleep(3000);
- } catch (InterruptedException e) {
- // TODO Auto-generated catch block
- e.printStackTrace();
- }
- return BitmapFactory.decodeResource(getResources(), R.drawable.abc);
- }
- @Override
- protected void onPostExecute(Bitmap result) {
- image.setImageBitmap(result);
- }
- }
- }
AsyncTask更新进度
AsyncTask约定了任务运行过程中,更新进度的回调方法,该方法并非抽象的,开发人员能够选择性地实现。
protected void onProgressUpdate(Progress... values)(该方法执行在主线程)
在任务运行过程中,能够调用publishProgress()方法提交进度,使得onProgressUpdate()方法被回调
实例
布局:
- <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" >
- <TextView
- android:id="@+id/tv_pb"
- android:layout_width="wrap_content"
- android:layout_height="wrap_content"
- android:text="100%"
- android:visibility="gone"
- android:textSize="16sp"/>
- <Button
- android:id="@+id/btn_update"
- android:layout_width="wrap_content"
- android:layout_height="wrap_content"
- android:layout_alignParentTop="true"
- android:layout_centerHorizontal="true"
- android:layout_marginTop="104dp"
- android:onClick="doAsyncTask"
- android:text="開始" />
- <ImageView
- android:id="@+id/iv_image"
- android:layout_width="wrap_content"
- android:layout_height="wrap_content"
- android:layout_below="@+id/btn_update"
- android:layout_centerHorizontal="true"
- android:layout_marginTop="22dp"
- android:src="@drawable/abs" />
- <ProgressBar
- android:id="@+id/pb_progress"
- style="?android:attr/progressBarStyleHorizontal"
- android:layout_width="fill_parent"
- android:layout_height="wrap_content"
- android:layout_alignParentTop="true"
- android:max="100"
- android:visibility="gone"
- android:layout_alignRight="@+id/btn_update"
- android:layout_marginTop="32dp" />
- </RelativeLayout>
LoadImage:
- public class LoadImage extends AsyncTask<String, Integer, Object> {
- private Context context;
- private ImageView imageview;
- private Bitmap image;
- private Button button;
- private ProgressBar pg;
- private TextView tv;
- public LoadImage(Context context, Button button, ImageView imageview,
- ProgressBar pg, TextView tv) {
- this.context = context;
- this.imageview = imageview;
- this.button = button;
- this.pg = pg;
- this.tv = tv;
- }
- @Override
- protected Object doInBackground(String... params) {
- for (int i = 0; i <= 100; i++) {
- publishProgress(i);
- try {
- Thread.sleep(50);
- } catch (InterruptedException e) {
- // TODO Auto-generated catch block
- e.printStackTrace();
- }
- }
- image = BitmapFactory.decodeResource(context.getResources(),
- R.drawable.abc);
- return null;
- }
- @Override
- protected void onProgressUpdate(Integer... values) {
- // TODO Auto-generated method stub
- pg.setProgress(values[0]);
- tv.setText(values[0] + "%");
- }
- @Override
- protected void onPostExecute(Object result) {
- imageview.setImageBitmap(image);
- button.setEnabled(true);
- pg.setVisibility(View.GONE);
- tv.setVisibility(View.GONE);
- }
- }
MainActivity:
- public class MainActivity extends Activity {
- private ImageView image;
- private Button button;
- private ProgressBar pg;
- private TextView tv;
- @Override
- protected void onCreate(Bundle savedInstanceState) {
- super.onCreate(savedInstanceState);
- setContentView(R.layout.activity_main);
- image = (ImageView) findViewById(R.id.iv_image);
- button = (Button) findViewById(R.id.btn_update);
- pg = (ProgressBar) findViewById(R.id.pb_progress);
- tv = (TextView) findViewById(R.id.tv_pb);
- }
- public void doAsyncTask(View view){
- button.setEnabled(false);
- pg.setVisibility(View.VISIBLE);
- tv.setVisibility(View.VISIBLE);
- new LoadImage(this,button,image,pg,tv).execute("");
- }
- }
AsyncTask是一个综合了任务的运行、进度更新、结果提交的类,使用AsyncTask
能够集中的编写某个异步任务的所有代码,而不必关心线程间的通信问题。减少了
编码出错几率,并有效的提高了代码的可阅读性、可维护性等。
小案例之异步载入图片
使用到的技术: Canvas(画布)、Paint(画笔)
Canvas(画布):用来决定画布的基础属性,运行绘制
Paint(画笔):设置颜色、设置字体、其它的设置
同一次画图过程中,可能须要多个画笔对象,或多次调整画笔的属性
使用Canvas:
public Canvas()
public Canvas(Bitmap bitmap)
public void drawRect(float left,float top,float right,float bottom,Paint paint)
public void drawBitmap(Bitmap bitmap,float left,float top,Paint paint)
public void drawText(String text,float x,float y,Paint paint)
使用Paint:
public Paint()
public native void setColr(int color)
public native void setAntiAlias(boolean aa)
public native void setTextSize(float textSize)
public void setTextAlign(Align align)
public Xfermode setXfermode(Xfermode xfermode)
AsyncTask