Android学习（二）--第二个项目遇到的问题

模拟后台程序运行进度提示

主要方法是用一个线程在后台发送数据，然后使用Handler处理数据。

每个线程都有且只有一个Handler，Looper。主线程默认有Looper了。Handler一定要重写handleMessage方法。在该方法中处理数据。

Handler h=new Handler(){
public void handleMessage(Message m){
Bundle b=m.getData();
int progress=b.getInt("progress");
progressBar.setProgress(progress);
textView.setText(String.valueOf(progressBar.getProgress()));
}
};

增加一个线程后台发送数据，注意最后要调用start()来调用run（），sendMessage需要参数Message，Message可以为空，setData参数为Bundle

@Override
public void onStart(){
super.onStart();
Thread t=new Thread(new Runnable(){

@Override
public void run() {
for(int i=0;i<20;i++){
try {
Thread.sleep(1000);
Message m=new Message();
Bundle b=new Bundle();
b.putInt("progress", i*5);
m.setData(b);
h.sendMessage(m);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
// TODO Auto-generated method stub

}

});
t.start();
}

完整代码

package com.example.homeworkprogress;

import android.app.Activity;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.util.Log;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.ProgressBar;
import android.widget.TextView;

public class MainActivity extends Activity {

private TextView textView;
private ProgressBar progressBar;
Handler h=new Handler(){
public void handleMessage(Message m){
Bundle b=m.getData();
int progress=b.getInt("progress");
progressBar.setProgress(progress);
textView.setText(String.valueOf(progressBar.getProgress()));
}
};

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
progressBar=(ProgressBar)findViewById(R.id.progressBar);
progressBar.setProgress(0);
textView=(TextView)findViewById(R.id.progressText);
}

@Override
public void onStart(){
super.onStart();
Thread t=new Thread(new Runnable(){

@Override
public void run() {
for(int i=0;i<20;i++){
try {
Thread.sleep(1000);
Message m=new Message();
Bundle b=new Bundle();
b.putInt("progress", i*5);
m.setData(b);
h.sendMessage(m);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
// TODO Auto-generated method stub

}

});
t.start();
}
@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);
}
}

遇到的问题：TextView的setText遇到找不到资源的异常。一开始setText用的是整形参数，后来改成字符串就好了。