android中懸浮顯示可拖動的歌詞欄

下面的示例是仿QQ音樂之類的歌詞欄，可以進行拖動和隱藏，代碼如下：

MainActivity：

package com.home.danglingactivity;

import android.app.Activity;
import android.content.Context;
import android.graphics.Rect;
import android.os.Bundle;
import android.view.Gravity;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.Window;
import android.view.WindowManager;
import android.view.WindowManager.LayoutParams;
import android.widget.Button;

public class MainActivity extends Activity implements OnClickListener {
	private MyTextView tv;
	private Button btn;

	@Override
	public void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		requestWindowFeature(Window.FEATURE_NO_TITLE);
		setContentView(R.layout.activity_main);
		btn = (Button) findViewById(R.id.main_btn);
		btn.setOnClickListener(this);
	}

	@Override
	public void onClick(View v) {
		if (tv != null && tv.isShown()) {
			hide();
		} else {
			show();
		}
	}

	/**
	 * 隱藏顯示歌詞的TextView
	 */
	private void hide() {
		WindowManager wm = (WindowManager) getSystemService(Context.WINDOW_SERVICE);
		wm.removeView(tv);
		btn.setText("顯示歌詞");
	}

	/**
	 * 顯示懸浮的TextView
	 */
	private void show() {
		Rect frame = new Rect();
		getWindow().getDecorView().getWindowVisibleDisplayFrame(frame);
		MyTextView.TOOL_BAR_HIGH = frame.top;
		WindowManager wm = (WindowManager) getSystemService(WINDOW_SERVICE);
		WindowManager.LayoutParams params = MyTextView.params;

		params.type = WindowManager.LayoutParams.TYPE_SYSTEM_ALERT
				| WindowManager.LayoutParams.TYPE_SYSTEM_OVERLAY;
		params.flags = LayoutParams.FLAG_NOT_TOUCH_MODAL
				| LayoutParams.FLAG_NOT_FOCUSABLE;
		params.width = WindowManager.LayoutParams.FILL_PARENT;
		params.height = WindowManager.LayoutParams.WRAP_CONTENT;
		params.alpha = 80;
		params.gravity = Gravity.LEFT | Gravity.TOP;
		// 設置x、y初始值
		params.x = 0;
		params.y = wm.getDefaultDisplay().getHeight();

		tv = new MyTextView(MainActivity.this);
		wm.addView(tv, params);
		btn.setText("隱藏歌詞");
	}

	@Override
	protected void onDestroy() {
		WindowManager wm = (WindowManager) getSystemService(WINDOW_SERVICE);
		if (tv != null && tv.isShown()) {
			wm.removeView(tv);
		}
		super.onDestroy();
	}

}

MyTextView：

package com.home.danglingactivity;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.LinearGradient;
import android.graphics.Paint;
import android.graphics.Shader;
import android.graphics.Shader.TileMode;
import android.graphics.Typeface;
import android.view.MotionEvent;
import android.view.WindowManager;
import android.widget.TextView;

public class MyTextView extends TextView {
	private final String TAG = MyTextView.class.getSimpleName();
	public static int TOOL_BAR_HIGH = 0;
	public static WindowManager.LayoutParams params = new WindowManager.LayoutParams();
	private float startX;
	private float startY;
	private float x;
	private float y;
	private String text = "我是不是你最疼愛的人，你為什麼不說話，握住是你冰冷的手動也不動讓我好難過";;
	private float float1 = 0.0f;
	private float float2 = 0.01f;
	WindowManager wm = (WindowManager) getContext().getApplicationContext()
			.getSystemService(Context.WINDOW_SERVICE);

	public MyTextView(Context context) {
		super(context);
		this.setBackgroundColor(Color.argb(100, 140, 160, 150));
	}

	@Override
	public boolean onTouchEvent(MotionEvent event) {
		// 觸摸點相對於屏幕左上角坐標
		x = event.getRawX();
		y = event.getRawY() - TOOL_BAR_HIGH;
		switch (event.getAction()) {
		case MotionEvent.ACTION_DOWN:
			startX = event.getX();
			startY = event.getY();
			break;
		case MotionEvent.ACTION_MOVE:
			updatePosition();
			break;
		case MotionEvent.ACTION_UP:
			updatePosition();
			startX = startY = 0;
			break;
		}
		return true;
	}

	@Override
	protected void onDraw(Canvas canvas) {
		super.onDraw(canvas);
		float1 += 0.001f;
		float2 += 0.001f;
		if (float2 > 1.0) {
			float1 = 0.0f;
			float2 = 0.01f;
		}
		this.setText("");
		float len = this.getTextSize() * text.length();
		Shader shader = new LinearGradient(0, 0, len, 0, new int[] {
				Color.YELLOW, Color.RED }, new float[] { float1, float2 },
				TileMode.CLAMP);
		Paint p = new Paint();
		p.setShader(shader);
		p.setTypeface(Typeface.DEFAULT_BOLD);
		canvas.drawText(text, 0, 10, p);
	}

	/**
	 * 更新浮動窗口位置參數
	 */
	private void updatePosition() {
		// View的當前位置
		params.x = (int) (x - startX);
		params.y = (int) (y - startY);
		wm.updateViewLayout(this, params);
	}
}

布局xml:

權限：